Heat Pumps Are Still A Good Investment Even If Your Grid Is Powered By Coal

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There are lots of people who think it does no good to electrify things like cars and home heating equipment if the electricity they use comes from coal-fired thermal generating stations. After all, it is widely understood that coal plants create more carbon emissions than any other thermal generation technology. Do heat pumps lower emissions if they run on electricity from a dirty grid?

Absolutely, according to researchers at the National Renewable Energy Laboratory. They modeled the entire US housing stock and found that, over the appliance’s expected lifetime of 16 years, switching to heat pumps for heating and cooling slashes emissions in every one of the contiguous 48 states.

In fact, heat pumps reduce carbon pollution even if the process of cleaning up the U.S. grid moves slower than experts expect. The NREL team used six different future scenarios for the grid, from aggressive decarbonization (95% carbon-free electricity by 2035) to sluggish (only 50% carbon-free electricity by 2035.) Their work was published last month in the journal Joule.

Here is the summary of the findings:

Electrification of fossil fuel combustion in buildings is a key component of achieving global greenhouse gas emissions targets. We use physics simulations of 550,000 statistically representative households to analyze distributions of the costs and benefits of three air-to-air heat pump performance levels, with and without insulation upgrades, across the diversity of the US housing stock.

We find positive greenhouse gas reductions in every US state for all performance levels across five 2022–2038 electric grid scenarios, with full adoption reducing national emissions by 5%–9%. We find that air-to-air heat pumps could be cost effective without subsidies in 59% of households (65 million).

That conclusion bears repeating. Substituting heat pumps for thermal heating sources could lower total carbon emissions in the United States by between 5 and 9%. Can you think of any other technology available to individuals that can do that? Sure, electric cars could. Yeah, upgrading insulation and sealing cracks can do wonders for lowering emissions.

But heat pumps can eliminate a big chunk of the nation’s carbon footprint, even if they are not powered by renewable energy and people can do this on their own. Incentives contained in the Inflation Reduction Act can help.

According to Canary Media, in 2023 renewable energy sources provided just 21% of U.S. electricity generation with nuclear energy coming in at 19%. The other 60% of power came from burning fossil fuels, so the grid in most parts of the US is still a major source of carbon pollution.

Heat Pumps Slash Carbon Emissions

The NREL researchers found that heat pumps lower household annual energy emissions an average by 36 to 64% — or 2.5 to 4.4 metric tons of carbon dioxide equivalent per year per housing unit. That’s a staggering amount of emissions. For context, preventing 2.5 metric tons of CO2 emissions is equivalent to not burning 2,800 pounds of coal. That’s the same as not driving your car for half a year or switching to a vegan diet for 14 months.

Eric Wilson, senior research engineer at NREL and lead author of the study, told Canary Media, ​“I often hear people saying, ​‘Oh, you should wait to put in a heat pump because the grid is still dirty,’ but that’s faulty logic. ​It’s better to switch now rather than later — and not lock in another 20 years of a gas furnace or boiler.”

The same analysis applies to electric cars. According to Yale Climate Connections, even in West Virginia, where over 90% of the electricity comes from burning coal, electric cars still use about 33% less energy than gasoline. EVs charged in West Virginia also reduce carbon pollution by 30%.

Emissions savings tend to be higher in states with colder winters and boilers and furnaces that run on fuel oil. Maine is a leader among US states with cold winter weather. There, heat pumps have proven so popular there than the state already exceeded its goal for the adoption of heat pumps two years ahead of schedule. A dirty grid doesn’t cancel out a heat pump’s climate benefits. That’s the importance of the NREL study.



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Air Source & Ground Source Heat Pumps

A 2023 analysis from climate think tank RMI further backs up heat pumps’ climate bona fides. Across the 48 continental states, RMI found that replacing a gas furnace with a heat pump begins lowering emissions the very first year it is installed and every year thereafter for all of its useful life.

Both the RMI and NREL studies focused on air source heat pumps, which pull heat from the outdoor air and can be three to four times as efficient as gas furnaces. But ground source heat pumps are becoming more popular and can be more than five times more efficient than gas furnaces, unlocking even greater greenhouse gas reductions.

NREL has created an online interactive dashboard you can use to determine how much switching to heat pumps will lower carbon emissions in the home in each state.  In the ​states tab, you can filter down to your state, building type, and heating fuel. For instance, based on a scenario of moderate grid decarbonization in the state of Colorado, a single family home that replaces a gas furnace with a heat pump could slash emissions by a whopping 6 metric tons of carbon dioxide every year.

Rewiring America’s personal electrification planner uses more specific info about your home and is also a useful resource, as is any energy auditor or whole house decarbonization company that calculates emissions savings as part of a home energy audit.

One final takeaway Wilson shared — if every American home with gas, oil, or inefficient electric resistance heating swap those things out for heat pumps, the emissions of the entire U.S. economy would shrink by 5% to 9%. That’s how powerful a decarbonizing tool heat pumps are.

The Takeaway

If there is a message here, it is that you don’t have to wait for the electrical grid in your area to be supplied 100% by renewables before you make the switch to heat pumps or electric cars. Both are so much more efficient than gas boilers, oil furnaces, or conventional cars that their benefits in lowering carbon emissions outweigh the impact of the dirtiest grids. Heat pump water heaters only increase the benefits available to home owners.

The word is getting out. According to data from the Air-Conditioning, Heating, and Refrigeration Institute, Americans bought 21% more heat pumps in 2023 than methane burning gas furnaces. That’s the biggest lead heat pumps have opened up over conventional furnaces in the two decades since the trade group started keeping records.

If the US is going to lower its total carbon emissions significantly, heat pumps will be an essential part of that process.


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