Convert from gas to electric space heating2008-08-07 by Rob
If your home is heated by a combustible fuel such as gas or oil, and if most of your electricity is generated from hydro, then it may be well worth considering switching to electric space heating. Perhaps you have an inefficient older furnace and you have been considering upgrading it, but are hesitant due to the large capital investment. You might be surprised to find that if you turn off your furnace, a couple hundred dollars worth of portable electric space heaters can get you through the winter and pay for themselves in reduced heating costs in the first year alone.
Calculate your “critical efficiency”
Combustion based heating systems are inherently inefficient compared to electric space heating. Here is a simple calculation you can do to determine the “critical efficiency” below which it makes economic sense to switch to electric space heating. First, determine your actual cost per kWh (kilowatt hour) of fuel. Call this value “A”. You may need to convert from some other unit of measure. For example, my home was designed to be heated with natural gas which is measured in GJ (gigajoules) on my statement. A quick internet search shows that 1 GJ is equivalent to 277.8 kWh. If possible base the value of A on actual statements, not advertised costs. In other words, A equals your total cost of fuel for a year divided by your total consumption in kWh for the same year. For me A worked out to about 0.043 $/kWh. Next, determine your actual cost per kWh of electricity consumed. Call this value “B”. Again, use your actual cost of electricity for a full year divided by your total electrical consumption in kWh for the same year. For me, B worked out to about 0.071 $/kWh. Next, recognize that A is not your “TRUE” cost. In any combustion based central heating system, some of those kWh of energy that you paying for never make it into your home. Much of the heat simply goes up the chimney. Some newer furnaces approach 100% efficiency but the heat distribution system still has losses compared to electric space heating since electric space heating puts heat exactly where you need it while central heating systems heat up non-living spaces which then dissipate additional heat to the outside. Thus a central heating system will always have a lower efficiency than electric space heating in the same home.Â If you take A and divide it by B you get your “critical efficiency”. If your combustion heating system is less efficient than A/B then you will save money by switching to electric space heating. My critical efficiency was about 60%.
Estimate your current combustion heating efficiency
How do you determine the efficiency of your combustion heating system? About the best you can do (without actually switching to electric space heating temporarily to compare results) is to make an educated guess. The efficiency of newer furnaces is often indicated right on them. However, as mentioned above this is only the efficiency of the furnace. You must also take into account the efficiency of the heat distribution system. If you have an 80% efficient furnace, with forced air distribution, you might assume 70% overall efficiency compared to electric space heating.In my case I guessed that my gas furnace and forced air heating system, having been built and installed 30 years ago might be around 60% efficient. This is the same value as my critical efficiency. Therefore, it seemed questionable whether I would realize a benefit from switching to electric space heating. In the name of science, I was willing to take the risk.
Calculate how much power and how many heaters you need
Based on your previous year’s fuel statements, you can determine the maximum continuous power you’re likely to need to heat your home. For example, I knew from previous gas statements that the most gas I ever consumed in one month was about 16 GJ or about 4445 kWh. Dividing that by 720 hours per month gave me a maximum continuous power output of 6 kW. However, this is an average over an entire month. Peak power requirments could be higher on a day to day basis, so I multiplied by a factor of 1.5 to get 9kW. This is based on gas heating though, so factoring in my estimated 60% efficiency, I figured I should only need about 5.4 kW of peak power output from my space heaters.I did not want to draw too much power from any one circuit in my home. A typical 15 Amp circuit can only drive up to 1600W before you risk tripping the breaker. Allowing for other electrical loads on any given circuit, I decided I did not want any single space heater to draw more than 750W. Thus I needed around 7 space heaters, each connected to a separate circuit in order to get the 5.4 kW of total heat output I wanted. I was in no hurry so I watched for sales and ended up picking up six 750W heaters for $25 each and two 1500W heaters (with a half power setting) for $40 each. These were oil filled radiator style heaters like the one shown to the right. I chose this style because it is completely silent (another benefit over forced air systems).
Make the switch and compare your results
I heated my home for an entire winter with the 8 space heaters described above. Comparing my energy consumption and costs to the previous winter I found that I saved about $350, easily covering the cost of the heaters. What’s more I determined that my gas heating system was actually less than 50% efficient compared to electric space heating. It’s important when comparing two different years to account for possible differences in outside temperature. To see how this is done and for more detailed data from my comparison over two consecutive winters, see Comparing natural gas vs electric heating. I also compared green house gas emissions.
Tricks to improve comfort
At first, I did not find my home very comfortable using electric space heaters, but things quickly improved. There is a bit of an art to getting an even temperature distribution. Effectively each heater has two variables you can control: it’s location, and it’s thermostat setting. With 8 heaters going simultaneously, that’s 16 variables to play with.I found that the most even temperature distribution could be achieved by placing the heaters near exterior walls, especially under windows. That may sound wasteful since the heat has a shorter path to exit the home, but it is the only way to get even temperature distribution. If you locate the heaters far from outside walls, the temperature will drop sharply as you move away from the heater towards the outside walls. The best method I found for adjusting the thermostats was to set them to their maximum and wait for the room to heat up a couple degrees above the desired temperature. Then I turned the thermostat down until the heater just turned off (indicated by a barely audible clicking sound). This thermostat position would typically result in the room cooling down a couple degrees and then holding at that temperature.
Heating on a schedule
If you are accustomed to using a programmable thermostat for your home to set back the temperature while you are away, you can implement a similar system with electric space heaters simply by plugging them into mechanical timers like the one shown. However, be aware that if the heaters are off for a particular fraction of the day, then the peak power output you need increases by the same fraction. For example, I determined I needed a maximum of 5.4 kW of power output to heat my home. If I turned my heaters off for 1/2 the day, then I would need a maximum of 10.8 kW of power while the heaters were on. Yet another benefit of electric space heaters is that you can “program” each space independently. For example, I work at home, so I can heat my bedroom at night but not during the day and I can heat much of the rest of the home during the day but not at night. It takes some time to bring a room up to temperature. Be sure to adjust timers to start heating earlier than when you want a room to be comfortable. Trial and error will suggest an adequate preheating time.
Testing the waters
It’s not necessary to invest in 8 space heaters all at once to see if electric space heating will work for you. A great way to test the waters is to buy just a couple heaters and run them in parallel with your central heating system. If you perform this test at the beginning of or end of your heating season, the space heaters will likely be providing most of the power to heat your home. The thermostat for your central heating system will automatically reduce its contribution. You can then compare a month of operating with partial electric heat to a previous month of operating with only your central heating system. Be sure to compare months with similar outside temperatures (or normalize the two costs by dividing by them by the actual average temperature difference maintained between inside and outside during each month). If partial electric heating reduces your “cost per degree”, then purchase more heaters and turn off your combustion based heating system completely.
What about your carbon footprint
You’ll notice that in the very first paragraph, I said you should consider this if your electricity is generated from hydro. That’s because electricity generated from hydro results in far less greenhouse gas emissions per kWh than any combustion process. Switching from heating your home with a combustible fuel to heating your home with hydro generated electricity will significantly reduce your carbon footprint. However switching to heating your home with electricity generated by a combustion process (ex coal fired power plants) will likely increase your carbon footprint. Chances are good it won’t make sense economically either. In any case, I recommend switching to electric space heating only if your electricity is generated by hydro.
Wouldn’t it be better to install a heat pump
Many readers have asked me if I have considered installing a heat pump. I have considered it and I am still considering it. Whether it is better or not depends on your definition of better. It is certainly better for the environment, but it involves a high capital cost, a significant amount of work, and many years till pay back (even with govâ€™t rebates). Is it worth it? Yes. Would I expect an average reader to switch to a heat pump because I said so. Not likely. If you can afford to switch to a heat pump (or even a high efficiency gas furnace) and you expect to be around to reap the benefits after the pay back period then by all means do it. But that is a big decision while switching to electric space heating is a no brainer (if you have an old, low efficiency gas furnace like mine). It costs a couple hundred dollars, takes almost no time to set up, pays for itself in a single winter and you can take the whole system with you if you move.