Comments on: Super insulate your hot water tank

By: rick

rick — Sat, 17 Jul 2010 20:20:17 +0000

I’m in the market for a new hot water tank, and would like to switch from propane to electric so that I can not only super-insulate, but also preheat with solar. I have tons of sun shine almost year round, and my chief goal would be to be able to keep that water hot enough throughout the night as to be able to shower in the morning, and replenish the tank with hot water from the roof during daylight hours (still in the planning stages, though). Thanks for documenting all of this.
Rick

By: Jeff

Jeff — Sun, 16 May 2010 20:05:40 +0000

To be considered when building a new home or upgrading an old home:
Super-insulate the home enough such that the capital cost of the heating/cooling equipment is drastically reduced.

If you don’t need a heater/cooler, you can save thousands on capital cost and instead ‘pipe’ it into insulation costs. The best news is that there is no running cost for insulation.

By: jim

jim — Sat, 08 May 2010 00:03:05 +0000

There are a few other factors to consider.If you are in a climate where you use the heat more than the air- I refer to actual balance of heat- not time. you are not saving as much. Also, depending on if your heat system is an exchange system or pure electric. In a house with heat strip heating and electric heater(and heater is running), you save almost nothing as long as airflow is good and the WH is not up against an outside wall. I live in FL so, insulation helps in 2 ways- lower water heater cost and lower cost on A/C since it does not have to cool the extra air the WH is heating. I have a heat exchanger that gets the water hotter than the electric as long as the air is on . The WH is unplugged 8 months of the year and the water is super hot all summer. The water(even at 120)is able to remove much more heat than the 95 degree air outside, which in turn lowers the A/C portion of the bill!

By: Rob

Rob — Thu, 19 Nov 2009 09:29:59 +0000

Hi Dan,
You’re right to question your friends and builder. 10″ walls will definitely reduce energy consumption. It’s just a question of how long it will take for the additional cost of insulating to be payed back in reduced energy costs.

Because insulation lasts for the lifetime of the home, the “moral” choice is to design for a payback period equal to the lifetime of the home. I don’t know for certain, but based on my calculations it seems that recommended R-Values (R20 walls and R40 ceilings) are based on about a 20 year payback. If you expect your home to last 40 years or more, you could double the recommended R-values and still achieve payback over the lifetime of your home.

I added some more information to the original article since a couple people have asked about home insulation. Thanks for your comment.

By: Dan Pearlman

Dan Pearlman — Thu, 19 Nov 2009 02:40:13 +0000

Do you know of any similar tests for wall insulation? I want to build a new house with 10″ think walls and as much insulation as I can get. My assumption is that a well insulated wall and ceiling will pay for itself in low heating / cooling costs and inert insulation requires no maintenance during the life of the house. My builder ( and several friends) say that insulation will only go so far. Once you have insulated to around R 40 in the ceiling and R20 in the walls, you loose any advantage.

That does not make sense to me. But does anyone actually know the optimum amount of insulation to install?

thanx

Dan

By: Rob

Rob — Tue, 29 Sep 2009 21:41:18 +0000

Hi Markus,
The bent element is surprisingly robust. I think if you experienced the bending process and held the final result in your hands you would have more confidence in it. The likelihood of a short seems no greater than in it’s original application as a stove element. Steel pots are used on these elements all the time, with a danger of electrocution to any person touching the pot if the element ever shorted out so I think these elements are designed to be quite safe in that regard.

I don’t recommend super-insulating a gas hot water tank (with open flue) unless you first convert it to electric and cap the flue as I did. The dangers are much greater (explosion, fire and carbon monoxide poisoning) with a gas tank, and the gains from adding insulation are much less since several hundred watts are dissipated into the tube at the center of the tank and up the chimney regardless of how much you insulate the outside of the tank. This loss cannot be eliminated without capping the tank (which cannot be done safely while it is operating on gas).

Thanks for your comments.

By: markus

markus — Sat, 26 Sep 2009 15:16:08 +0000

very interesting info here, i am always in favor of messing with basic and mass products to maximize gain and efficiencies. The transformation of the gas heater sounds quite rigged tho, i am not sure if i would be comfortable with a bent up old element as my heating element which may short out on the inside of the tank. Also if you super insulate a gas hot water tank, care must be taken to not impede the air intake and outlet where heat and flame may pose a fire hazard. i in the past superinsulated a very small electrical tank and it used next to NO power at all. I used a vapor barrier and cardboard to hold the insulation reasonably consistently around the tank. Cardboard makes a wonderfully fitting cover for the insulation batts but again, watch the flame/fire hazard.
Nice work, impressive and highly useful for those of us able to rig things, kinda dangerous for some who THINK they are Mr. Fix-it’s tho, lousy craftsmen, keep clear and don’t burn down your families!! Admit if you are NOT that guy and keep safe. Thanks for pursuing this info at a time critical for our planet to reduce energy consumption, wake up North America, it’s time to do this type of stuff!!

By: Rob Steves

Rob Steves — Mon, 02 Feb 2009 07:46:48 +0000

Hi Pondered. Thanks for the comment. That is an interesting idea. Depending on the size of the home, the climate, weather-tightness, I think you might find that the optimum insulation thickness is reached more quickly in the case of a home than in the case of a hot water tank. This is because in the case of a home there are some free heat sources: solar gain, occupant body heat, lighting and other electrical appliances. At a certain insulation thickness, the cost of heating will drop to zero. I haven’t done the math to figure out what that thickness might be for a typical home, but I do recall reading an article about a person in eastern Canada who built a passively heated solar home with 11″ of insulation in the walls and he found he paid $200-$300 in heating bills per year. He built his walls as a 2×6 framed inner wall and another 2×6 framed outer wall, with the studs out of phase. He also used a continuous, unbroken vapor barrier between the two walls, with all electrical and plumbing routed on the inside of the vapor barrier, resulting in an extremely well sealed building envelope.

By: Ponderer

Ponderer — Mon, 02 Feb 2009 07:24:19 +0000

Interesting results. It would be neat to see a similar calculation for the optimum amount of insulation to use when building a house. I bet if you target a 10-15 year payback, it probably makes economic sense to put 1 to 2 ft of insulation in the walls and 2-3 feet of insulation in the attic. Of course the cost calculation would also need to factor in the additional lumber and the reduced square footage of living space due to thicker walls. Great post.