ALTERNATIVE ENERGY SOURCES FOR HEATING OUR HOUSE

Last week we had our Energy Audit visit but it will take a few weeks to get the detailed report. During the visit, the Auditor used an IR camera to confirm that we do have some blown-in insulation in our exterior walls. He said there was some evidence of insulation settling but that it wasn’t too bad. He estimated the R-value of the walls to be R11 or 12, not far from my assumption of R10. He did say his report would recommend more attic insulation, basement exterior wall insulation, a heat pump, and an electric water heater amongst other things. When he did the fan blower test, he mentioned that our house wasn’t as “leaky” as he thought it would be, so that is good news.

His visit got me thinking more about alternative energies to heat our home, their relative cost and CO₂ emissions. According to https://www.selectaglaze.co.uk/the-benefits-of-retrofitting-houses, the average house in the UK emits at least 5000 kg of CO₂ per year. As the figure indicates, the site suggests that a deep retrofit of a house could reduce CO2 emissions down to 1000 kg of CO₂ .it would be interesting to see how our current house configuration compares to this and what we could do to reduce emissions, could we get down to 1000 kg of CO₂?

, We don’t have natural gas on our street so I won’t consider that possibility. That means we are down to oil, propane, or electricity. One important feature of our old house is that it heats by hot water baseboard. Through some research, I have come to realize that this severally limits our options for alternative energy sources, particularly when considering the switch to electricity. For example, solar panels, wind turbines, and heat pumps cannot be used to produce the 160 to 180 °F hot water needed to feed our baseboard heating system. So the options available that would continue to heat our home through the hot water baseboard system are high-efficiency oil, propane, or electric boilers.

 

Alternative Boilers Energy Costs

As our calculations from the last posting showed, it currently takes about 61 MBTU to heat our old house and an estimated 16 MBTU to provide hot water. The Efficiency Nova Scotia website indicates that modern electric, propane, and oil boilers have efficiencies of 100%, 93 and 95% respectively. Again, according to ENS, we get 36,500 BTU per liter of oil, 24,300 BTU per liter of propane, and 3412 BTU/kwh for electricity. So we can calculate the usage of each energy source as shown in the 3^rd column of Table 1 below. From ENS the cost of electricity is $0.1615/kwh which is close to the current cost of electricity in winter 2023. Oil cost $2 per liter and propane costs around $0.85 per liter. Therefore, the cost comparison is shown in the 4^th column of the table below. The current cost of heating our home assuming a 70% efficient furnace (i.e., 87.6 MBTU or 2400 liters) would be $4800 per year. So all new boilers would result in a cost reduction with the propane furnace giving the lowest cost.

Table 1. Some comparative data for alternative energy

Type of Boiler	Efficiency	Amount of use	Cost of Energy	CO2 emissions	Reduction in CO2 emissions
Electric (100% eff.)	61 MBTU	17878 kwh	$2887	9022 kg	-2566 kg
Oil (100% eff.)	63 MBTU	1726 liters	$3452	4643 kg	1813 kg
Propane (100% eff.)	66 MBTU	2716 liters	$2308	4101 kg	2355 kg

 Alternative Energy CO₂ emissions.

One of the benefits of propane is that it is a cleaner burning fuel. It emits 1.51 kg of CO₂ per liter of propane  https://www.eia.gov/environment/emissions/co2_vol_mass.php . Using the same source for comparison, furnace oil emits 2.69 kg of CO₂ per liter. For our house, this would result in a total CO₂ emission per year of 4643 and 4101 kg for high-efficiency oil and propane respectively. Our current 70% efficiency oil furnace produces 6456 kg of CO₂ for heating, so the new oil or propane furnaces would provide a net reduction in emissions. (see the 5^th and 6^th columns of Table 1 for the details).

Electricity is a harder source to nail in terms of CO₂ emissions. Perhaps the “cleanest” electricity comes from hydroelectric plants. According to https://www.hydropower.org/factsheets/greenhouse-gas-emissions, a hydro plant produces 24 g of CO₂ per kwh. For the situation of our house, this would result in 429 kg of CO₂ per year which is 10 times smaller than that for new oil and propane furnaces. Unfortunately, Nova Scotia Power currently burns fossil fuels (including coal) to produce 70% of it’s electricity, the remainder being from renewable energy sources. One major disadvantage to burning fossil fuels (FF) to produce electricity is that at best it is only 40% efficient. (https://www.mpoweruk.com/fossil_fuels.htm#). This means that for every unit of electrical energy produced, you need to burn 2.5 units of fossil fuel. I will assume that no CO₂ comes from the renewable energies used by NSP. Therefore, of the 17,878 kWh we need to heat our house, 12,514.6 kwh will come from burning fossil fuels which will produce CO₂. Since this FF to electricity conversion is only 40% efficient, providing 12,514.6 kwh of electricity will actually require 31,286.5 kwh of energy from FF. This translates to 106 MBTU which is about 1.7 times more than what we use by directly burning either oil or propane in a boiler to heat the house!

Let’s go to the next step of CO₂ emissions. According to the NSP, 50% of their FF comes from coal and 50% from oil. The site (https://www.eia.gov/environment/emissions/co2_vol_mass.php) lists the CO₂ emissions of various fuels in terms of MBTU. Coal emits 96.1 kg of CO₂ per MBTU while oil emits 74.1 kg of CO₂ per MBTU. IF NSP uses a 50:50 split then on average their FF usage to produce electricity would be 85.1 kg of CO₂ per MBTU.  Therefore, the total CO₂ produced to provide the 106 MBTU of FF used to produce the 12514.6 kwh needed for an electric boiler to heat our home is 9022 kg. An electric boiler would produce about twice as much greenhouse gas as high-efficiency oil and propane boilers. In fact, as shown in the last column it would produce more CO₂ than our current 70% efficient oil furnace. Interestingly, a high-efficiency propane furnace results in the highest reduction in greenhouse gas emissions.

The CO₂ produced by an electric furnace is a crazy calculation, can it be right? I compared these calculations to those provided on the ENS website. For example, they calculate that a house using 80 MBTU’s to heat using an electric boiler, would emit 12,360 kg of CO₂ while the use of a high-efficiency oil and propane furnace would emit 5670 and 4940 kg of CO₂ respectively. Those CO₂ ratios, 2.2 and 2.5 compare very well to the 1.9 and 2.2 from my calculations in Table 1. In fact ENS indicates that the electric boiler performance is even worse than my calculations indicate. So, in the current situation, it makes no sense to switch to an electric boiler, in fact, it would be damaging to the environment to do so.

You might say this is not a fair calculation since NSP is increasing its use of renewable energy all the time. According to NSP, when Muskrat falls reaches its full potential the FF usage to produce electricity will drop to 40%. By 2030 NSP projects that only 20% of its electricity will use FF. We can repeat the above calculation for these cases. At 40% and 20% FF usage, 7151 kwh and 3576 kwh respectively of the of the total 17878 kwh needed to heat our home would come from FF. With the 40% efficiency conversion of FF to electricity, this would climb to 17878 and 8940 kwh for 40 and 20% FF usage respectively. Converting these energies to MBTU results in 61 and 31 MBTU and 5191 and 2638 kg CO₂ emissions respectively. So bringing Muskrat falls online still does not produce less CO₂ than high-efficiency FF furnaces, going to 80% renewables would definitely make an electric boiler more environmentally friendly. According to my calculations, the break-even point when an electric boiler would produce the same CO₂ emissions as a high-efficiency propane furnace would be when NSP uses 68% renewables to produce electricity. In another calculation which I won’t detail here, I compared the total CO₂ emissions if we switched to a propane furnace versus an electric boiler today. From the above calculations, the propane furnace would emit much less CO₂ than the electric furnace due to the high usage of FF by NSP. As NSP migrated to more renewables, this would favor the electric furnace in terms of CO₂ emissions. However, it would take until the year 2042 before the net emissions from the electric furnace were the same as that produced by the propane furnace over those same 20 years. I conclude that there is no scenario where an electric furnace makes sense to heat your home in Nova Scotia from the point of view of CO2 emissions at least at this stage. Maybe it would make sense 10 to 15 years from now when NSP achieves its 80% renewables target.

Thanks for wading through the calculations. Hope you find it useful.