By: Cary Weiner, October 23rd, 2018
This is Part 2 of a 2-part series on all electric homes. This post focuses on the carbon costs and benefits of going all-electric, while Part 1 focused on the financial costs and benefits.
As electric vehicle sales continue to soar, there’s also been a growing buzz in the sustainable energy world about fully electrifying buildings. The theory is that we can electrify almost everything and then produce that electricity with clean, cheap, renewable electricity from wind, solar, hydro, and battery storage. It’s a compelling argument on the surface, so we thought we’d dig a little deeper into costs and benefits to fully electrify homes.
The chart above compares annual household energy emissions for homes heated with natural gas (conventional) versus electric air source heat pumps (HP) at different emissions rates. It also includes a comparison of carbon emissions for energy efficient homes with those same heating fuels. Emissions rates are shown in pounds of CO2 per kilowatt-hour. Colorado’s electric grid (which in reality is connected to the grid of the entire western U.S.) currently emits 1.45 lbs./kWh compared to 1.0 for the U.S., 0.5 for California, and 0.2 for the hydropower-based state of Washington.
ASHPs can reach efficiencies of 200%, meaning that for every unit of energy they use, they can produce two units of energy. Natural gas heaters, by contrast, have maximum theoretical efficiencies of under 100% and many older furnaces and boilers are 80% efficient or less.
However, the chart shows that homes heated with natural gas emit less carbon than homes heated with air source heat pumps in Colorado (but the opposite is true for the other geographic regions). As Colorado continues to decarbonize its electric grid, homes heated with electric heat pumps will see a carbon benefit versus homes heated with gas. By 2021, for instance, Xcel Energy projects that its emissions rate will fall to 1.09 lbs./kWh, making emissions from homes heated with gas even with homes heated by air source heat pumps. Interestingly, once emissions rates get down to California’s level, even highly energy efficient homes heated with natural gas will emit more carbon than standard homes using air source heat pumps.
Of course, homes that use heat pumps may also choose to go solar in order to get to net zero (or close to net zero). This “bypass” of the electric grid has the greatest carbon benefits, but would come at a higher financial cost.
- Conventional = 80% efficient furnace, 0.6 EF water heater, 10 SEER air conditioner
- Heat pump (HP) = 10 HSPF, 18 SEER, 2.2 SEF
- “30% EE” refers to homes that use 30% less energy than standard homes