Unfortunately Canada’s electoral system is broken. We do not have proportional representation so for most Canadians, voting for who you like in this election is as good as not voting at all. If you want your vote to count, you need to vote strategically. Currently, a very possible outcome of the election is a Conservative majority which would be the absolute worst case for the environment.

If you want to make your vote count for the environment, your best option is to vote AGAINST a Harper majority by voting for whoever has the greatest chance of defeating the conservative candidate in your riding. You can find out who that is at  www.projectdemocracy.ca (you can also consult www.catch22campaign.ca, last time, and www.leadnow.ca.).

Make no mistake. This election is bigger than your local riding. You are either voting for a Harper majority or you are voting against it. Set local issues and candidate preferences aside and think federally when you vote on May 2.

John says:

I have read your blog and another one you commented on about using Coroplast for thermal collector panels with great interest. I think Coroplast is an excellent material for a collector mainly because of it’s higher temperature tolerance. My wife tested baking a sample at 250 degrees F and it came out feeling just about as rigid as normal. We also filled it with water and put it in the freezer and it did not deform from the ice.

I am however concerned about freezing problems, more due to glued joints at the ABS pipe at the top and bottom of an assembled panel bursting. I plan to have a large holding tank of water used directly with the panels without a heat exchanger to the holding tank so I’m not too interested in using a bunch of anti-freeze. I am planning to build a drainback system using these panels, and just painting them black.

I also saw that polypropylene does not tolerate UV light well and will become brittle and break after long exposure. Coroplast can however be made special order with a UV absorber mixed in with the polypropylene. I am getting some regular Coroplast from a local sign shop that does not have the UV protection, so I’m looking into paints that absorb the UV. If the prototype works well I’ll look into getting UV protected Coroplast for additional panels.

And a couple weeks later:

My wife and I finally got one of these built and tested.  We built it as a drainback system and used plain water dyed black using pond dye.  We did not paint the panel.  We got frosted tempered glass panes from Craigslist to build this and the next ones.  We used an old hot water circulator pump also from Craigslist.

We did a 4 hour test on a clear day, readjusting the panel angle a few times during the test.  The full spreadsheet is available but I was not sure if it could be posted here.  It is a 1.814 square meter panel with 37.85 liters (10 gal) of water in the system.  We used a 55 gallon plastic drum for the tank.  The tank and hoses were not insulated.

Starting temp was 53.8 F. At the 1 hour mark the temp was 92.7 F, average power was 952 watts, 52% efficient. At 2 hours, 117 F, 768 watts, 42%. At 3 hours, 127 F, 593 watts, 33%. At 4 hours, 130 F, 464 watts, 26%.  We also did a stagnation test with no water in it, and it got up to 152 degrees F on a 45 degree day.  We are looking forward to mounting it permanently and testing reliability/longevity.  One thing we still need to do is get UV clear paint to help protect the panels from UV breakdown, and see if that affects the efficiency much.

Full panel and storage tank

Panel draining back into storage tank

Panel and storage tank showing water pump

Thanks John for sharing your results.

For some time I’ve been considering the best way to deal with a pile of scrap wood that has been growing next to my home, the result of many woodworking and carpentry projects I’ve been involved in over the years. A few options I have considered are:

1. taking it to the landfill
2. cutting it into chips and using it as mulch
3. burning it

From a climate change standpoint, the latter of these is surprisingly the least harmful in the long run. Mulching or burying do postpone carbon release to the atmosphere, but the carbon will be released eventually regardless. What’s worse, mulching or burying the wood will result in some anaerobic decomposition (that is decomposition in an oxygen deprived environment) which will result in the production of methane, a far more harmful greenhouse gas than carbon dioxide.

Burning also has a side benefit. It releases energy which may be captured and put to some use. Scrap wood and yard trimmings are burned in backyards across the country each year without any attempt to capture that useful energy. Rather than simply “disappearing” my pile of scrap wood, I wanted to extract as much value as possible by heating my home with it. To do so most efficiently, I built an ultra-efficient wood burning stove, more commonly referred to as a “rocket stove’. Rocket stove designs are most often used for small cook stoves but larger stoves for home heating are not unheard of. They are often referred to as rocket mass heaters.

Warnings

Fire is dangerous. Building and operating your own wood stove of any design will almost certainly void any fire insurance you may have on your home and may also pose a serious risk to you and your family. As far as wood stoves go, a rocket stove is probably one of the safest designs since the combustion chamber is tiny, the exhaust volume is low, the draft is strong, and the bulk of the exterior of the stove does not reach very high temperatures. However, as with any combustion appliance, there are some precautions you should follow.

0. Locate the stove well away from anything flammable. At least 18″ is recommended by most building codes for ordinary fireplaces and wood stoves.

1. Keep a watchful eye on your stove whenever it’s burning. With an average load of wood my stove burns for about 30 minutes before requiring more fuel. I consider this short burn time to be not a burden but a safety feature, and I don’t mind it at all since there’s a certain pleasure that comes from putting another log on the fire.

2. Don’t burn treated or manufactured woods. Treated wood, plywood, OSB, etc all contain chemicals that will be released into the exhaust during combustion. You certainly don’t want to breath these and you probably don’t want to put them into the atmosphere. You should only burn untreated solid wood.

3. Install a smoke detector. Smoke detectors are required by most building codes, so you probably already have one. However, if you build a rocket stove for heating a garage or outbuilding, you should probably install a smoke detector there as well.

4. Install a carbon monoxide detector. All combustion appliances are capable of producing carbon monoxide which can be deadly if it is released into your home. Other combustion appliances in your home such as a furnace or hot water tank are probably a greater carbon monoxide threat that the rocket stove described in this article since they operate continuously, unattended, even while you sleep. That said installing a carbon monoxide detector is a wise precaution.

How is a rocket stove different from a regular wood stove?

The goal of a rocket stove is to burn a relatively small amount of wood at as high a temperature as possible, resulting in more complete combustion, and to extract as much heat as possible from the exhaust gases. To generate high combustion temperatures, rocket stoves separate the combustion, heat extraction and exhaust functions. They have insulated internal chimneys to generate a strong draft for vigorous combustion. My design uses a down draft combustion chamber. Scrap wood is loaded directly on top of the existing burning wood inside the combustion chamber.  The flame is drawn downward by the strong draft rather than rising out of the chamber as one might expect. The result is that ALL combustion products pass through the hottest part of the fire resulting in very complete combustion, producing the greatest amount of heat and reducing products of incomplete combustion such as carbon monoxide and smoke. To capture as much of the heat as possible and radiate it into the room, the exhaust gases are passed through a secondary chamber (much larger than the combustion chamber) that absorbs and radiates the heat. Finally the relatively cool exhaust gases are expelled through an exhaust tube.

The following illustration shows the basic design.

Insulating the chimney ensures a large temperature difference between the exhaust gases inside the chimney and those outside it. This temperature difference causes a density imbalance resulting in a strong draft. The hot exhaust gases in the chimney rise, while the cooler exhaust gases outside the chimney fall, and the whole process draws fresh air into the combustion chamber, supporting vigorous combustion. In my design, the radiating chamber is about 18″ in diameter by about 36″ high, while the combustion chamber is only about 4″ by 4″ by 10″. Don’t let the overall size of the stove fool you. It only burns a couple handfuls of wood at a time. The large size is required to absorb and radiate the heat, not to contain the fuel.

Construction

Rocket stove mass heaters are often built from steel drums. These are convenient since they have a flat top that can also be used for cooking. I did not have one handy though. What I did have was my parents’ old electric hot water tank that they had just replaced since it was corroded and leaking. In addition to this I used some 3″ diameter steel pipe, some 4″x4″ square tubing, and some flat steel plate, all about 1/8″ wall thickness (though that is probably thicker than necessary). I also used some flexible aluminum tubing (dryer ducting) to feed the exhaust from the rocket stove into my existing fireplace.

Above is a picture of the internal parts of the stove (combustion chamber and chimney) set up for initial testing to make sure it would generate enough draft for vigorous combustion. The aluminum flex tubing is connected to the top of the chimney for testing only. In the finished product it will be connected to the side of the stove. The chimney is insulated with about 1″ of Roxul (a rock wool insulation that will tolerate higher temperatures than fiberglass insulation) and wrapped with adhesive aluminum furnace tape to hold the insulation in place.

The above image shows the hot water tank cut to accept the combustion chamber and chimney.

The above image shows the combustion chamber and chimney being welded into the side of the hot water tank. Note the block of wood between the end of the chimney and the inside surface of the tank to ensure an appropriate gap for the exhaust gases. This piece of wood will be removed after the chimney is welded in place.

Mad scientist at work…

… and after a bunch more welding and a paint job that I neglected to take any pictures of … viola! … the finished product. The silver band around the bottom isn’t a racing stripe. It covers the seam where I tack welded the bottom of the tank back on. I did not want to weld it on permanently since I may want to disassemble the stove later for inspection.

Notice that I removed a glass pane from the left door of my fire place and replaced it with cardboard. The aluminum flex tube passes snugly through a hole cut in the cardboard to expel the exhaust gases into the fireplace where, still warm, they rise and exit through the existing chimney. I know you’re probably thinking I must be crazy to use a combustible material like cardboard for this purpose, but the fact is that the exhaust volume from this stove is so low and the stove is so efficient at removing heat from the exhaust that this aluminum tube reaches a maximum temperature of only about 60 degrees C during operation. That’s cooler than a typical cup of coffee. The top of the stove gets much hotter, of course.

I also made a simple metal screen that can be placed over the combustion chamber to prevent sparks from popping out into the room where they could ignite something (or more likely just leave burn marks as they smolder on the carpet). I have another cover, not shown, that is a solid steel plate. It’s useful to quickly extinguish the fire and to prevent air infiltration when the stove is not in use.

Above is a photo of the cleanout. The plate which makes up the bottom of the combustion chamber is removable. I just slide it out as shown in the photo and the ash drops into any suitable receptacle (I’m using a plastic tray above). I’ve found it best to clean the ash out every week or so as once there is more than about a cup full it will fill the bottom of the combustion chamber and start to build up in the tube between the combustion chamber and the internal chimney. Then it’s a little harder to get to and it will eventually start to reduce the draft. In hindsight, access through the side of the combustion chamber instead of the bottom would have been more useful.

Does it work?

Well… actually … it works too well. The difference between burning wood in the fireplace and burning wood in this stove is incredible. You really have to experience it to believe you can get so much heat from a small handful of wood. I’ve fed my fireplace for hours with hardly any change in room temperature but it only takes a few minutes for the rocket stove to raise the room temperature noticeably. It may take a long time to get through all my scrap wood at this rate. Feeding the stove every evening after work, I have only managed to go through about one bin (perhaps 20kg) of wood per week. Part of the issue is the season. It just doesn’t take much heat to get the house to a comfortable temperature right now in early spring. I will be able to burn a lot more wood in the stove next winter.

Savings

On average the heat energy available from burning wood is around 4.5 kWh per kg (assuming a 20% moisture content). Assuming roughly 80% efficiency of the stove (just a rough guess) the heat extracted will be about 3.5 kWh per kg. I heat my home with electricity that costs about $0.07 per kWh. Therefore, the heating value of my scrap wood is about $0.25 per kg and by burning about 20kg per week I save about $5 per week on heating costs or about 50% of my heating bill for this time of year. Savings will be much greater in winter when the stove can be operated more frequently without the room becoming uncomfortably hot.

Why not just buy a fireplace insert?

I considered buying a fireplace insert but after learning about rocket stoves I quickly dismissed the idea because:

1. an insert would almost certainly be less efficient
2. it would require significantly more cost and effort to install
3. it wouldn’t provide nearly the same conversation value
4. I would not be able to re-purpose existing waste material such as my parents hot water heater
5. it would not be portable (I look forward to operating my rocket stove on our patio on cool summer evenings).

What about adding thermal mass? Would that be more efficient?

Wood stoves used as a primary heat source for a home will derive significant benefits from thermal mass (imagine replacing my short length of aluminum flex tube with 30 or 40 feet of duct buried inside a couple tons of concrete and you’ll have the right idea). The thermal mass stores heat and releases it slowly into the home, evening out the temperature and allowing the stove to be operated intermittently.

However, for a stove like mine that’s used only for supplemental heating, thermal mass is not of much benefit since an even temperature can be maintained simply by varying the heat input from the primary system (which happens automatically since it is controlled by a thermostat). For example, when I operate my rocket stove in the winter, my electric heaters automatically cut back such that the house temperature does not rise significantly.

It is also worth noting that thermal mass, by itself, does not improve efficiency. Improved efficiency is often a side effect of adding thermal mass, but the improvement is really just a result of extracting more heat from the exhaust gases. This could be accomplished just as easily without adding any thermal mass. For example, I could extract more heat from my exhaust simply by using a longer piece of aluminum duct between the stove and fireplace (I have noted that the exhaust temperature drops about half way to ambient for every 20cm of tube length).

So in a nut shell, thermal mass is not really that useful for a stove that’s intended for use only as supplemental heat, if the primary heating system is on a thermostat.

Further reading

There is a lot of good information on rocket stoves online. A Google search on “rocket stove” or “rocket mass heater” will yield good results but http://www.rocketstove.org is probably the best place to start. There is also an excellent book called Rocket Mass Heaters available for purchase in PDF format at http://www.rocketstoves.com. There are also several videos online of rocket stoves in action. Search for them at http://www.youtube.com.

Reader Projects

If anyone out there decides to build a rocket stove based on this or a similar design, I would be happy to post some pictures of your project, or if you have your own site, let me know and I will post a link below.

2010-12-13: One reader, Brent, built his own rocket stove following a similar design (though he was clever enough to put the cleanout in the side of the combustion chamber rather than the bottom). You can read more about his stove in the comments, or take a look at some pictures and a video on Brent’s blog: http://streetjesus.blogspot.com/2010/12/rocket-mass-heater-project.html.

Happy burning!

In this post I will look at the only energy input: fuel.

Work, Energy, and Power

Before looking at fuel, it’s worth defining a few terms that I will be using throughout this series of posts. “Work”, “energy”, and “power” are terms used frequently and sometimes interchangeably by the general populace, but in an engineering context, they have specific meanings that must be understood. For a greater understanding than I provide here, follow the links to Wikipedia articles.

Work is a force applied over some distance. The amount of work is equal to the force multiplied by the distance. If force is measured in Newtons (N) and distance is measured in metres, then multiplying force by distance will give work in Joules (J). The Joule is a measure of energy. Work is a specific kind of energy. It can be thought of as energy used to move something.

Energy is a measure of the capacity to do work. It is also measured in Joules. Energy can take many forms (e.g., chemical, light, heat, work). Energy can be converted from one form to another through various means. In an engine, for example, the chemical energy of a fuel is converted to heat through the process of combustion and the heat is used to expand a gas against a piston, converting some of the heat to work.

Power is a “rate” of energy flow. Power is measured in Watts (W). It can be expressed as energy per unit time. 1 Watt is equivalent to 1 Joule per second. Since work is a form of energy equal to force times distance, and power is equal to energy divided by time, it follows that power is equal to force times distance divided by time. In other words, power is equal to force times velocity.

Just as power can be expressed as energy per unit time (e.g., 1W = 1J/s), energy may be expressed as power multiplied by time (e.g., 1Ws = 1J, 1Wh = 3600J or 3.6kJ, 1kWh = 3.6MJ) . You may be more familiar with energy expressed in kWh as this is a common unit of measurement used on utility bills.

I cannot emphasize enough how important it is to understand these terms and the formulas relating them. Without such an understanding, hypermiling is all just trial and error.

Energy Density of Fuels

A certain volume of fuel contains a certain amount of chemical energy that can be released by combustion. Energy density is a measure of the chemical energy per unit volume or per unit mass of fuel. Energy is specified in kWh (recall 1kWh = 3.6MJ), volume is specified in litres, and mass is specified in kg. Thus energy density of fuels is commonly specified in kWh/litre or kWh/kg.

The table below shows energy densities for some fuels you may be familiar with:

I drive a gasoline vehicle, so for every litre of fuel consumed, 9kWh of energy is input to the vehicle and the law of conservation of energy requires that all energy losses in the vehicle energy flow chart above must total 9kWh. Hopefully it’s clear that the way those 9kWh of energy are divided between the various energy losses will have a significant effect on vehicle mileage. Of specific interest is the fraction of energy “spent” on overcoming rolling resistance and drag since those are the only “necessary losses” to move the vehicle.

Aside: Whenever I encounter energy specifications like this, I like to do a quick cost comparison. For example, I know from my utility bills that I pay about $0.07 per kWh for electricity. I pay about $1.00 per litre for gasoline. Since gasoline contains 9kWh per litre, I effectively pay $1.00/9 = $0.11 per kWh for gasoline. This is one among many of the reasons why I don’t burn gasoline to heat my home and why I’m considering building an electric vehicle.

Although it’s conceivable that the energy density of a fuel may be manipulated by additives, this is generally not attempted by hypermilers and would be a poor place to start for the beginner. Also note that energy density is not related to octane level.

Unfortunately it appears that our first stop on the energy flow diagram hasn’t yielded any techniques or modifications a driver can use to improve their mileage. However, the important thing to take away from this post is that the energy density of a fuel is fixed and that for gasoline specifically, it is 9kWh/litre or 12.8kWh/kg. I’ll be coming back to those numbers again in later posts to convert calculated energy losses back to litres of fuel consumed, which is what hypermilers are really interested in.

Stay tuned for Chapter 3 – Engine Losses which I promise will be more exciting since there ARE a lot of driving techniques and vehicle modifications you can use to improve engine efficiency.

Hyper-what?

Hypermilers are drivers who attempt (often obsessively) to extract every possible mile (or kilometre… up here in Canada) from a tank of gas, whether through driving techniques or vehicle modifications or both. I first started experimenting with hypermiling in 2007, having gleaned some information from websites and forums such as http://www.gassavers.org, http://cleanmpg.com, and http://www.ecomodder.com. I have a strong background in engineering and science (a B.A.Sc and M.Eng. from the University of British Columbia and I’ve been working in the field of Electrical and Mechanical Engineering for 12 years). Though the information on the above sites was a useful starting point, I found that much of it is was obvious and much of the rest of it was misguided. Some techniques are presented that produce good results, and there are certainly many members achieving excellent mileage, but the explanations given for the phenomena at work sometimes make my eyes roll. In a forum format it is difficult for an average reader to distinguish voices worth listening to from those that aren’t. My experience has been that there is a general lack of understanding of the science behind hypermiling and there is no single source where the science is explained in detail. That is something that I hope to correct through this series of posts.

Why do it?

First, let’s state the obvious. If you want to consume less fuel, the surest way to do it is to drive less. However, even walking and biking result in fuel consumption. I’ve heard it said that a meat-eating cyclist is responsible for more fossil fuel consumption per mile traveled than a vegetarian SUV driver. While I’m not certain of the validity of that statement, it does illustrate a point. A person’s effective fossil fuel consumption goes well beyond what they burn directly. In any case, the intent of this guide is not to discuss the merits of driving or not driving. I will leave it to the reader to determine that for themselves.

If you do drive I will assume you may be interested in reducing your fuel consumption. Perhaps you wish to save money. Perhaps you wish to save the environment. Perhaps you wish to reduce your dependence on foreign oil. Perhaps you are just looking for a worthy obsession. One of the best explanations for hypermiling I’ve seen comes from MetroMPG (an active member of several online forums – see his website at http://www.metrompg.com). He says:

No, it’s not just for the money.

I calculate fuel consumption on each tank of gas because it’s a challenge. It’s a high performance activity; a technical skill; a game, like GT4 and sail boat racing.

In my university days, I took a number of car racing courses. All of which boiled down to: “how to apply a few rules of physics to your driving technique in order to squeeze the maximum possible speed from a given radius, without skidding off into the weeds.” The feedback was hearing the tires sing just the right song through the curves, and out-pacing other drivers in identical cars.

Economy driving is just a different kind of performance driving: “how to apply a few rules of physics to your driving technique in order to squeeze the maximum possible distance from a given amount of fuel.” The feedback is the numbers at each fill-up, and (hopefully) beating the ratings. Plus the satisfaction of knowing it’s much easier on the machinery, the environment, and the wallet (if you don’t go overboard with efficiency mods).

It doesn’t have the instant gratification of screaming through the curves… but it’s not going to cost me my license either. Driving at the limit of grip is something safely done on the track, but driving efficiently is a game you can play anywhere, all the time.

Does it really work?

Given the number of fuel saving scams out there, I wouldn’t be surprised if you’re skeptical. I was skeptical when I started too. I had heard it said by many that the most significant gains could be had simply by changing one’s driving style. I thought I was an “economic” driver and I was skeptical that I could achieve significant improvements just by changing the way I drove. After a little research, calculation and experimentation I discovered just how wrong I was. In hindsight it seems obvious. The way we are taught to drive – the way auto manufacturers intend their vehicles to be driven – simply isn’t an efficient way of converting fuel to kilometres. In the first year after I started hypermiling, I improved my mileage from 40 MPG to 65 MPG without any vehicle modifications other than the addition of a vacuum gauge (the proper use of which I will describe in Chapter 3). In the remainder of this series I hope to describe how you too can squeeze the maximum possible distance from a given amount of fuel, under real world driving conditions, without annoying nearby drivers (well… not too much anyway) and without spending more on vehicle modifications than you’re likely to save on fuel.

It’s all about energy

Hypermiling is all about conserving energy. Thus it can best be understood through a systematic exploration of the energy flows in a vehicle. The first law of thermodynamics, often referred to as the law of conservation of energy, states that for a closed system whose internal energy remains constant, the total energy input must exactly equal the total energy output. Energy in = Energy out. Considering a vehicle as a closed system, energy is input in form of fuel. Energy flows through the system from engine to gearbox to drivetrain to wheels, etc. At each step along this flow, some energy is output from the system in the form of heat. Thus there are many paths through which energy is output from the system. The energy flow can be represented graphically as I have done in the diagram below.

The first law of thermodynamics requires that for a given distance traveled, the combined total of all energy outputs in the above diagram must exactly equal the energy input in the form of fuel.

Aside: The astute observer may note that the underlying assumption that the internal energy of the system is constant isn’t entirely true. The speed of the vehicle, the level of charge of the battery and the altitude all affect the internal energy of the system. However, these effects can be ignored as long as the vehicle is in the same state (same speed, altitude and level of charge of the battery) whenever the energy inputs and outputs are measured. Note that the amount of fuel in the tank does NOT affect the internal energy of the system since I am considering the gas tank as being OUTSIDE the system. Instead, I consider fuel as entering the system when it passes through the fuel injector. This allows more precise comparison of input to output energy and does not require that we consider the fuel in the tank as an internal energy of the system.

Note that to move a vehicle, the only losses which MUST be overcome are rolling resistance and air resistance (drag). If you were to push a vehicle by hand instead of driving it, you would be supplying the energy input. Rolling resistance and drag would be the only energy losses. Rolling resistance and drag are losses imposed by the environment from outside the system. All other losses are just an indirect result of the methods employed within the system in an attempt to overcome rolling resistance and drag.

A certain amount of fuel consumption can be attributed to each energy loss. It is a useful analogy to think of each energy loss path as a virtual hole in a your gas tank that fluctuates in size in response to your actions (vehicle speed, engine RPM, engine load, braking habits, etc). Every drop of fuel you put in your tank eventually exits the system through one of these “holes”. Hypermiling, at its heart, is the art and science of plugging the holes (at least partially) through driving techniques and vehicle modifications. The remainder of this series will be a systematic exploration of the energy inputs and outputs shown above. I will attempt to follow the outline below (I’ll change these to links as I post new information):

Chapter 1 – Introduction and outline
Chapter 2 – Fuel
Chapter 3 – Engine Losses
Chapter 4 – Drivetrain Losses
Chapter 5 – Braking Losses
Chapter 6 – Rolling Resistance
Chapter 7 – Air Resistance (Drag)
Chapter 8 – Alternator and Electrical Losses
Chapter 9 – Miscellaneous Additional Losses
Chapter 10 – Summary

Hopefully I will be able to post a chapter every couple weeks. In each chapter I’ll discuss:
1. The science that describes the phenomenon including the equations governing the energy flow.
2. How to measure the energy losses on your own vehicle to determine parameter values for the equations.
3. Driving techniques and vehicle modifications to reduce the energy losses.
4. The degree of reduction achievable for the particular energy loss, and the effect on overall fuel consumption.
5. Results from some of my own experiments.

If you have comments related to topics that I haven’t covered yet, please save them until the related topic is posted. Consider subscribing to my RSS feed and/or email notifications via the link on the main page if you want to be notified as each chapter is posted.

Stay tuned.

We (my wife and I that is) keep the temperature in our home relatively low in winter. As I’m writing this, it’s a balmy 16 degrees C in my living room. My lovely wife is wearing a toque and she’s about to put on another sweater because she’s feeling “a bit of a chill”, but she’s a trooper and wouldn’t have it any other way. That’s how she was raised. In Richmond, BC, where we live, winters are… well… wet. It’s pretty much a case of 100% relative humidity outside 24/7 and the water table is at ground level… well… truthfully sometimes it’s a few feet above ground level, but that’s why we have the pumps.

Combine 100% relative humidity outside with low temperatures inside and as you might expect, we occasionally have issues with condensation, especially on windows. “Experts” generally don’t recommend keeping interior temperatures below about 17 degrees C for exactly this reason. I don’t care much for expert opinions (experience has convinced me that I’m more expert than most of them), but I also don’t care much for condensation.

A solution with a bonus: free energy

The solution (without simply raising the temperature of our home),  is a dehumidifier. While I purchased it for its intended purpose (to reduce humidity levels) I now realize that it also makes a very effective heater. Ah… but doesn’t it cost money and energy to operate a dehumidifier? Well… actually… NO! At least not in the winter, when we’re heating our home with electricity anyway. In fact, a dehumidifier is MORE efficient than an ordinary electric heater, which is already 100% efficient. Yes, a dehumidifier is more than 100% efficient at heating your home. That is to say the amount of heat a dehumidifier will release into your home is greater than the amount of electrical energy it will consume. The reason is simple: a dehumidifier removes energy from water vapor in the air in order to condense it to a liquid. This energy is released into your home.

It’s all about enthalpy

There is a property of any substance known as the enthalpy of vaporization. “Enthalpy” really just means energy. The enthalpy of vaporization of a substance is a measure of how much energy it takes to convert a given mass of the substance from a liquid to a gas. It also indicates how much energy is released when a given mass of the substance is condensed from a gas to a liquid. The enthalpy of vaporization of water is 2257 kJ/kg.

What is the efficiency?

How efficient is a dehumidifier at heating your home? Let’s figure it out together. I mean that literally. As I write this, I haven’t actually figured it out yet myself. I’m flying by the seat of my pants here, people; I’m a scientist gone rogue. But luckily I’m also a scientist who recently acquired a portable dehumidifier. I plugged it into a Kill-A-Watt meter several hours ago to measure exactly how much electrical energy (indicated in kWh by the Kill-A-Watt meter) it consumed. It’s been running for about 8 hours and it has consumed 3.87 kWh of electricity. Thus, based on the first law of thermodynamcis I know it has put at least 3.87 kWh of heat into my home.

However I have also determined with a simple digital scale that it has condensed 3.23 kg of water in that same time. How much additional energy did it release into my home as a result of that? That’s where the enthalpy of vaporization comes in. 3.23 kg multiplied by the enthalpy of vaporization of water (2257 kJ/kg) gives 7290 kJ of energy. A kWh is equivalent to 3600 kJ so 7290 kJ is equivalent to 2.025 kWh.

Thus, the total amount of heat released into my home by the dehumidifier over the last 8 hours is equivalent to the 3.87 kWh of electricity consumed, plus the 2.025 kWh of energy released by the condensation of water. The “efficiency” is equal to the energy output divided by the energy input or in this case (3.87 + 2.025)/3.87 = 1.52 or 152% efficiency. An efficiency over 100% is more appropriately referred to as a “coefficient of performance” since technically, it is impossible to achieve greater than 100% efficiency (having more than 100% efficiency in energy conversion would defy the first law of thermodynamics). So if you ever measure more than 100% efficiency, as I just did, what it really means is that you have moved energy from one place to another rather than simply converted energy from one form to another. Such is the case with a dehumidifier which removes energy from water vapor and releases it into the home in the form of heat, condensing the water to liquid in the process. But whatever the terminology you want to use, the fact remains that I can release 1.52 kWh of heat into my home for every  1 kWh of electricity my dehumidifier consumes.

What’s the payback time?

I paid about $250 CAD for my dehumidifier. It consumes about 480W of electricity (3.87 kWh in 8 h) and outputs about 730W of heat (480W*1.52) into my home. I can buy a decent electric heater that will output 730W for about $50. So the difference in price is about $200. Let’s calculate the difference in the cost to operate. A 730W electric heater consumes exactly 730W of electricity. The dehumidifier only consumes 480W of electricity to produce the same 730W of heat. The difference (730-480) is 250W. Effectively I get a free kWh (1000 Wh)of heat for every 4 hours of operation. I currently pay about $0.07 per kWh for electricty, so I save about $0.42 per day when operating the dehumidifier in place of a heater. My heating season runs from October through March, or around 180 days of the year. Therefore, I can save about 180*$0.42 = $75 per year by operating the dehumidifier in place of a heater. That will take a little over 2.5 years to pay back the difference in price of $200.

Will this work for anyone?

In a word, “No”. The human body is most comfortable at a relative humidity between 20% and 60%. I can run my dehumidifier continuously in winter and not expect to ever drop below 20% relative humidity inside my home. The same may not be true for homeowners in other locations maintaining their homes at higher temperatures than I do. Heating with a dehumidifier works for me because of the high relative humidity in Richmond, even in the winter, and because of the low temperature at which I keep the interior of my home. It could work well for anyone who lives in a similar environment and keeps their home at a low temperature. But if you live where temperatures are usually below 0 degrees C outside in winter then you likely have a much lower relatively humidity. In that case, a dehumidifier will not be able to condense nearly as much water for a given amount of input energy and its operation may bring the relative humidity below a comfortable level.

Clothes dryer vs a rack and a dehumidifier

If you’re considering hanging your wet clothing to dry inside your home, vs using your drier, then you should know that a dehumidifier will be far more efficient than a clothes dryer. In the case of a clothes dryer, electrical energy is used to vaporize the water in your clothing and the water vapor (and all the energy you’ve put into it) is expelled from your home through your drier vent. There is a net loss of energy from your home. If instead you use a dehumidifier, the heat already in your home is used to vaporize (evaporate) the water in your clothing. This energy is recaptured by the dehumidifier when the water vapor is condensed to liquid. Unlike the drier, the dehumidifier doesn’t expel any energy from your home.

Heat pump vs dehumidifier

A dehumidifier is effectively a heat pump. Rather than extracting heat from the ground or the outside air, a dehumidifier extracts heat from water vapor contained in a home’s inside air. In my home, for reasons given above, I can run my dehumidifier continuously without reducing the relative humidity in my home below a comfortable level and I’ve found the coefficient of performance (COP) is about 1.52. A typical air source heat pump has a COP of around 4 assuming an outside temperature of around 0 degrees C (a typical Richmond winter). A typical ground source heat pump has a COP of around 7 assuming a ground temperature of around 10 degrees C (a typical Richmond ground temperature). So clearly, a heat pump (either air or ground source) is much more efficient. If I had a heat pump, I would be consuming more energy than otherwise by operating my dehumidifier. That said, I feel secure in the knowledge that I can run my single dehumidifier continously and consume less energy to heat my home than if I were running an electric heater. I’ll save the installation of a heat pump for another day… perhaps.

Can you heat your whole home this way?

No. If I were to install more portable dehumidifiers to provide all the heat my home requires (to maintain a balmy 16 degrees C all winter long) I would almost certainly bring the relative humidity below comfortable levels, and the COP would drop below the measured value of 1.52 simply because there isn’t enough water vapor in the air to be condensed. So the idea of using a dehumidifier to heat one’s home is clearly not scalable. At best a dehumidifier may provide suplemental heat. I think  I might get away with using two portable dehumidifiers continuously which would each save me about $75 per year based on the calculations above. That’s about $150 per year in total. Currently, that’s about 10% of my home’s annual heating bill.

I’ve known for some time that BC Hydro is a net exporter of power. When we do import power it’s because the US will sell it to us cheaply during their off-peak hours in exchange for being able to buy it back during peak hours. Their coal fired power plants can’t change their output as quickly as the change in daily demand, so they use BC’s hydro power to even out the peaks and valleys.

I am infuriated by the Campbell government’s attempt (apparently successful) to manufacture consent for privatizing power production in BC by convincing BC residents that WE need the extra power for OUR use. WE DON’T!!! End of story.

In his article, Raif points out that even if we did need the extra power, private hydro projects will produce most of their power during spring run off, exactly when we don’t need it. Therefore, the only possible value in private hydro is the export market, especially given Obama’s mandate to find clean energy sources for the US. As Raif put it:

Our rivers, up to about 700 applications now, will be butchered to warm California swimming pools. Moreover, once we embark down this slippery slope we’re in this forever. We will be, like Bre’r Rabbit, stuck to the tar baby.

For an idea of what those 700 applications look like, here’s a map (courtesy of Private Power Watch):

Don’t get me wrong. I think that hydro power IS a clean, renewable resource and it SHOULD be developed further in BC, even for export purposes. Climate change is everyone’s problem and I will concede the possibility that “butchering our rivers” could be the lesser of many evils that could be done to help meet the worlds growing demand for power.

But… and this is a REALLY BIG BUT… why in the world would we not want to retain ownership and control over the resources we’re exporting. How could we be so short-sighted that we’re willing to relinquish ownership of our natural resources premanantly and irrovocably to private corporations. Once these resources are removed from the commons, there’s no going back. We’re giving up control over resources that might come in pretty darn handy as the world runs out of fossil fuels over the next couple centuries. The privatization of BC’s power generation is nothing but a short term cash grab that we will almost certainly regret when we have to compete with the US to purchase the power being generated on our own soil. And hydro power is not the only issue. Wind and other renewable power sources are also at risk.

It’s about situations like this that I often hear people remark “One day our grandchildren are going to look back and wonder what the hell we were thinking”. I WISH that were the case but the sad fact is that our grandchildren likely won’t even know what they’re missing. It is exactly this lack of cross-generational accountability that frees each generation to sacrifice the future of the next.

If you are a BC resident concerned about the privatization of BC’s power, I strongly urge you to write your MLA. For more information and other ways to get involved, check out the Save our Rivers Society and www.hydrofactsbc.ca and Private Power Watch.

No funds will be allocated toward climate programs, let alone carbon offset strategies, which is a huge oversight. See my post BC’s Carbon Tax – So close yet so far from a few months ago for more details on that. The tax itself is not high enough to significantly reduce people’s consumption of fossil fuels, adding only 6% to the current price over the next 5 years. Seasonal variation and increasing world crude oil prices have resulted in an increase in price of about 16% over the past 3 months alone. That’s almost 3 times the increase that will be imposed by the BC carbon tax over the next 5 years.

I’m happy to see fuel prices rising because that kind of increase IS likely to make people rethink the amount of fossil fuel they consume, and indeed, “alternative” modes of transportation like walking, biking, and public transit are on the rise. I will not be surprised if the government takes credit for this in the following years, even though the trend has been well established before their tax has even taken effect. But the fact remains that the fuel that is consumed will not be any more “climate friendly” or “carbon neutral” once the tax is imposed. That is, unless people choose to make it so by spending their rebate wisely.

This year a $100 Climate Action Dividend cheque will be mailed to every British Columbian. A website called Green Your Campbell Cash has been developed by The Tyee, the Western Canada Wilderness Committee, Voters Taking Action on Climate Change, the David Suzuki Foundation and the Pembina Institute with the intent of diverting at least some of the $440 odd million dollars of rebates to strategies that will actually have a climate impact. If you’re wondering what to do with you’re $100 rebate, or if you have a climate project and are looking for funding, check out the website.

Originally posted at www.IWillTry.org.

From its extraction through sale, use and disposal, all the stuff in our lives affects communities at home and abroad, yet most of this is hidden from view. The Story of Stuff is a 20-minute, fast-paced, fact-filled look at the underside of our production and consumption patterns. The Story of Stuff exposes the connections between a huge number of environmental and social issues, and calls us together to create a more sustainable and just world. It’ll teach you something, it’ll make you laugh, and it just may change the way you look at all the stuff in your life forever.

While 20 minutes is hardly enough time to touch on all the issues, this film does a great job and sends an overall positive message. Click the image below to see the film.

The intent of the tax is to reduce consumption of fossil fuels by making them more expensive. No funds are actually allocated toward climate programs, let alone carbon offset projects so the fuel that is consumed will not be any more “climate friendly” or “carbon neutral” than before.

So… will people consume less fuel as a result of the carbon tax? Let’s do a quick calculation. It takes about 428 litres of gasoline to produce 1 tonne of CO2 equivalent GHG emissions. Gasoline prices in BC are around $1.17 per litre. So it costs a consumer about $500 to buy enough gasoline to produce 1 tonne of GHG. The BC carbon tax will increase that cost by $10 or 2% in the first year, increasing to $30 or 6% by 2012.

Does the BC government really believe that a 6% increase in fuel costs over 5 years is likely to cause anyone to reduce their fuel consumption?

I think not. One might expect a corresponding 6% decrease in fuel consumption, but more likely there will be no noticeable effect at all. Just look at the past 5 years. According to BCGasPrices.com, since 2003 gasoline prices in BC have increased around 70% (from about $0.70 per litre in 2003). That has had little noticeable effect on people’s fuel consumption, so what effect is an additional 6% increase over the next 5 years likely to have? I think none whatsoever.

Let’s do another calculation. There are carbon offset strategies (most notably methane capture from landfills, animal waste, or decaying plant matter) that offer proven, quantifiable GHG emission reductions for as little as $5/tonne (see www.carbonfund.org). At that rate the BC carbon tax of $30 per tonne would be enough to offset the GHG emissions from fossil fuel consumption 6 times over. According to a 2007 report, fossil fuels account for nearly 80% of BC’s GHG emissions. Therefore, if the carbon tax were put towards effective carbon offset and emissions reduction projects instead of being paid back to us in the form of reduced income tax, it appears that BC would be able to decrease its GHG emissions by almost 500%. In other words, BC could become carbon NEGATIVE, practically overnight if the carbon tax were spent in a useful manner.

How Gordon Campbell could come so close to doing something so good and then miss the mark entirely is beyond my comprehension. What is also beyond my comprehension is the level of praise he’s receiving for it. Hasn’t anybody else run the numbers?

Originally posted at www.IWillTry.org.

An artist in Seattle, Chris Jordan, explores what the statistics of consumption actually look like. For example, what do 106,000 aluminum cans look like (that’s the number consumed in the US every thirty seconds)?

Cans Seurat, 2007

Full image (60″x92″).

Partial zoom:

Detail at actual size:

Visit Chris Jordan’s website for many more Images of Consumption. What do 426,000 cell phones look like (the number retired in the US every day)? See his website to find out.

Originally posted at www.IWillTry.org.

There is hardly any direct sunlight here (Vancouver, BC) over the winter but I hope to extract some heat in the spring and fall for home heating and much more heat in the summer to heat a hot tub. I’ll likely have far too much heat in the summer so I will be installing silvered mylar under many of the panels to reflect most of the sunlight (unless I can dream up some other use for all that hot water).

Anyway, a couple weeks ago I worked up the curiosity to measure the temperature of my solar attic. I measured at 3 hour intervals over a 24 hour period using a digital weather station with logging capabilities. I measured once on a cloudy day and once on a sunny day for comparison. The following plots show the results.

What should you put on your sign? It would be great to point people to a website such as www.IWillTry.org for more information, but it’s certainly not necessary. You can display any message you like that expresses your concern and inspires action. I created a simple wooden sign for display in my garden as follows:

1. Cut a piece of wood to a nice size. If you have a router, add a nice profile to the edges. Print your text on the sign with a black felt pen. Then stain the wood with the stain of your choice (or none at all).	2. After a few minutes, wipe off the excess stain with a rag and allow the sign to dry for an hour or so. Then brush on a thick coat of outdoor polyurethane and allow the sign to dry overnight.	3. Nail a sign post to the back and insert your sign in the location of your choice.

Here are a few additional words of advice:

1. If you’re promoting a website, be vague and intriguing. A viewer is more likely to visit a website out of curiosity after seeing a sign that says “www.IWillTry.org – Will you?” than out of a sense of moral obligation after seeing a sign that says “www.IWillTry.org – Help stop global warming!”.

2. Be visible but not obtrusive. You want something your neighbors and visitors will notice, and be intrigued by, but that they won’t be annoyed by if they have to see it every day.

3. If your sign will be placed outside, make sure it will stand up to the elements. Some possibilities are:

• concrete stepping stone with letters embedded
• painted wooden sign
• painted garden stone
• wooden plaque with text burned into it

4. Your creation will be all the more intriguing and influential if it is unique. Express your creativity.

Originally posted at www.IWillTry.org.

I have considered food-miles before from the perspective of reducing energy consumption and greenhouse gas emissions from food transportation, but after reading the book I was pleasantly surprised to learn of many other benefits experienced by the authors, Alisa Smith and James MacKinnon. I attended a talk on food sustainability at UBC where they were guest speakers and I found it truely inspiring, to the point where I’m not only trying to buying more locally produced foods, but I’m growing some myself.

Some of the things you can look forward to when you eat locally produced foods are:

1. Better tasting food
2. More social interaction
3. Getting in touch with the seasons
4. Discovering new flavours
5. Reducing energy consumption and ghg emissions
6. Supporting small farms
7. Giving back to the local economy
8. Feeling more healthy

For the complete list and other information, visit http://www.100milediet.org.

The purpose of this experiment is to determine your vehicle’s drag coefficient Cd and coefficient of rolling resistance Crr. This is done by measuring your vehicle’s speed as a function of time while coasting in neutral (also known as a coast down test).

Why would you want to know Cd and Crr for your vehicle? Well, suppose you’re interested in modifying your vehicle for improved fuel efficiency. You might consider modifications such as air dams, wheel skirts, removing mirrors, switching to low rolling resistance tires, etc. Cd and Crr offer a quantitative method of comparing vehicle performance before and after these types of modifications to see if you made any improvement.

Equipment

You will need the following equipment:

• a vehicle (and someone with a driver’s license)
• a clock or stopwatch
• a pen and paper (and someone other than the driver to record data)
• a flashlight (driving at night avoids traffic)
• a long stretch of flat road with little traffic or wind
• Excel or another spreadsheet application. I prefer OpenOffice Calc which you can download and use for free, but its Solver function does not handle non-linear systems (yet) so you’ll have adjust input variables manually by an iterative process to minimize the error between the model curve and your data (it’s not too hard, I promise).
• The spreadsheet I created to analyze the results. You can download it here: Drag_Coefficient.xls

Background Information

First, let’s define some quantities:

Fd is the force on the vehicle due to air resistance (drag) in Newtons
Frr is the force on the vehicle due to rolling resistance in Newtons
F is the total force on the vehicle in Newtons
V is the vehicle’s velocity in m/s
a is the vehicle’s acceleration in m/s²
A is vehicle frontal area in m²
M is vehicle mass including occupants in kg
rho is the density of air which is 1.22 kg/m³ at sea level
g is the gravitational acceleration constant which is 9.81 m/s²
Cd is the vehicle’s drag coefficient we want to determine
Crr is the vehicle’s coefficient of rolling resistance we want to determine

Now for some formulas:

Fd = -Cd*A*0.5*rho*V² (formula for force due to air resistance or drag)
Frr = -Crr*M*g (formula for force due to rolling resistance)
F = Fd + Frr (total force is the sum of Fd and Frr)
F = M*a (Newton’s second law)

Note that both Fd and Frr are negative indicating that these forces act opposite to the direction of the velocity. Note also that Fd is increases as the square of velocity. This is why driving at high speeds is much less efficient than driving at low speeds. Combining these formulas with a bit of algebra gives us the acceleration due to air and wind resistance as a function of velocity:

a = -(Cd*A*0.5*rho*V²)/M – Crr*g

Note that the acceleration is negative indicating that air and wind resistance will cause the velocity to decrease.

I created my spreadsheet (see Equipment section above for download) based on these formulas to generate a model of velocity vs time that can be compared to actual data. The model values for Cd and Crr can thus be adjusted until the model matches the data. This adjustment can be done manually, by overwriting the values of Cd and Crr with new values till the model matches the data, or it can be done using a “Solver” function.

Procedure

You can determine Cd and Crr from the same set of test data by measuring velocity with respect to time as your vehicle coasts in neutral. Note that Crr will not be pure rolling resistance but will include some drive-train resistance as well.

1. Drive to a flat road with little traffic or wind.

2. Have the passenger ready with stopwatch and paper to record data.

3. Have the driver accelerate up to above 70 km/h or so, and shift into neutral.

4. Record data as follows. The driver should indicate when the speed drops to exactly 70 km/h. At this time (t=0) the passenger should start the clock. The passenger should indicate every 10 seconds after that and the driver should call out the current speed to the nearest whole km. The passenger should record this value next to each time.

Aside: If you have a digital camera capable of recording several minutes of low resolution video (as most people seem to have these days), the process is much easier and more accurate. You don’t need any equipment except the digital camera. Simply have your passenger record a video of your speedometer during the coast down tests, or find some way of mounting the camera so you can do the recording without an assistant. Using a free program such as Avidemux (http://fixounet.free.fr/avidemux/) you can play the video back on your computer frame by frame and view the speeds at desired times.

5. Repeat the test in the opposite direction.

6. Repeat the test in both directions twice more (6 trials in all, 3 in each direction). All these values will be averaged for a more accurate analysis.

7. Download the spreadsheet I created (see Equipment section above) and enter all your data following the instructions included. The spreadsheet averages data from all 6 trials to create a single data set representing velocity (V actual) as a function of time. It then generates it’s own model for velocity (V model) based on entered constants and initial guesses for Cd and Crr. Excel’s “Solver” function can be used to adjust Cd and Crr in order to minimize the error between the model and actual data. If you are using OpenOffice Calc (which I highly recommend and which you can download for free from http://www.openoffice.org ), unfortunately, the solver function currently only handles linear systems, so you will have to adjust the input values manually to minimize the error between the model and the data. Once the error is minimized and the model data matches the actual data as best it can, then Cd and Crr are correct.

Results

Here are the quantities I measured for my car (a 1992 Geo Metro):

M = 1000 kg (about 850kg curb weight plus 150 kg of occupants)
A = 2.3 m² (a reasonable approximation based on measurements of my car)

A plot of velocity vs time is shown below. It is based on the averages from my 6 trials. You can see that the model curve closely matches the data points.

The values of Cd and Crr for the model are:

Cd = 0.370
Crr = 0.0106

Therefore, these are the drag coefficient and coefficient of rolling resistance calculated for my car.

These values are nice to know. However, in practice, if you want to compare performance before and after making modifications to your car, you can get faster results just by measuring the time to decelerate from speed A to speed B. Pick high to medium speeds if your modifications are likely to affect drag. Pick medium to low speeds if your modifications are likely to affect rolling resistance. Don’t forget to take multiple measurements in each direction and average the results.

For more experiments you can do on your car see my website IWillTry.org .

Update 2009-01-02

I’ve learned a lot since originally posting this 16 months ago. I’ve played with measuring Cd and Crr under different conditions on a number of vehicles and other experimenters have picked apart and tweaked my spreadsheet for their own uses.

My experience is that there IS a mistake in one of the underlying assumptions of the model: namely that the force of rolling resistance is constant independent of V. Vehicles are designed with negative lift (so they get pushed into the road more at higher speeds, improving handling) so the force of rolling resistance also has a component that varies with V like the drag force. The force of rolling resistance also includes a small component of viscous force (drivetrain) which varies with V.

The model assumes that the drag force is related only to V² and that the force of rolling and drivetrain resistance is constant. In reality the force of rolling and drivetrain resistance is also related to V2 and V. So a better model of the force on a moving vehicle is:

F = iV² + jV + k where i, j, and k are constants.

A curve based on that model more closely matches actual coast down data indicating it is a more accurate model. But after solving for i, j and k, there is no way to extract meaningful values of Cd and Crr since by definition, they assume i is related only to drag, and j is 0, neither of which is entirely true. To think of it another way, Cd and Crr values define a model which is only an approximation of the real world. A physical object doesn’t really have a drag coefficient. Only the model of the physical object does.

As mentioned above, if you want to compare performance of a vehicle before and after making mods, the difference in coast down time itself is more meaningful than the change in Cd or Crr extracted from coast down data.

Duct Sealing FAQ

Why is sealing ductwork important?

Leaky ductwork can account up to 30 percent of total heating and cooling costs. For an average home, leaky ducts can waste hundreds of dollars each year. While the increased energy costs and green house gas emissions are significant, health and safety are also a concern.

Why is duct leakage so common?

Most connections are simply not sealed. Those that are, may have been sealed with a poor quality material such as duct tape. Yes, ironically enough, duct tape is just about the worst material you could use to seal your ducts. Want proof, see these test results. If a tape is to be used, foil tape is a better choice. Even better is to use a mastic.

What is mastic?

A group of high strength adhesive compounds used in the building and construction trades. Usually applied by trowel, brush, or caulking gun. There are three general classifications: water-based; solvent-based; and two-component curing systems. Water-based is the safest and easiest to use. It performs as well and in some instances better than the other two classes.

If ducts are insulated, do they need to be sealed?

Yes. Insulation does not stop air leaks. Look for dirt streaks in duct insulation, they’re a sign that air has been leaking from the ducts.

Are certain types of ducts more air tight?

Studies show that all types of ductwork can have problems with air leakage. Mastic works to seal metal, flexible, and fibrous ductwork.

What are the most important areas to seal?

In order of priority, these are:
1. Disconnected components
2. Connections between the air handling unit and the plenums
3. All seams in the air handling units and plenums, takeoffs, boots, and other connections, especially site-built items.

What are the VOCs (volatile organic compounds) in mastics?

In water-based mastics, the only volatile compound is water which is inorganic. Therefore the VOCs are infinitesimally small (not recordable). This is the reason water-based mastics pose a low health risk compared to solvent-based and two-component mastics.

Where to check for leaks

Where to apply mastic

It is a good idea to apply mastic to all joints and seams, regardless of whether you can detect leakage. Thermal expansion and furnace vibration can loosen joints over time causing them to leak in the future unless they are sealed with a flexible material such as mastic. The following images show more detail about where to apply the mastic.

How to apply mastic

1. Clean duct Surface
   Use a cloth to wipe dust from the surface of the duct. If oily film or grease covers the duct, wipe clean with a damp cloth.
2. Apply the mastic
   For gaps less than 1/4″, load the brush with mastic and coat the entire joint with a continuous strip. Use the end of the brush to work the mastic into joint. Spread the mastic at least one inch on each side of the joint. The mastic should be thick enough to hide the metal surface of the duct (about 1/16 inch thick). If the gap in the duct connection is larger than 1/4 inch use a fiberglass reinforcing membrane in addition to the mastic. If the membrane is sticky on one side, cut enough membrane to cover the joint, press the membrane in place, then cover it with mastic. Apply enough mastic to completely cover the membrane. If the membrane does not have a sticky side, first apply a thin layer of mastic, press the membrane into the mastic, then apply a finish layer of mastic.
3. Wrap Ducts with insulation
   Water-based mastics generally dry to the touch in 2 to 4 hours. Insulation may be installed over wet mastic but try not to move the ducts too much, because the mastic seal could be damaged. All duct support work should be done before applying mastic.

Where to buy mastic

You can buy mastic suitable for duct sealing from the following companies (please add to this list):

RCD Corporation
Home Depot – If this link doesn’t go to the proper product page, try searching for “duct sealant” or “mastic” on the Home Depot website.
Other