This story was originally published by Canary Media.
You might consider heat pumps as a tantalizing climate solution (they are) and one you can adopt yourself (many have). But maybe you’ve been waiting to get one, wondering how much of a difference they really make if a dirty grid supplies the electricity you use to power them—that is, a grid whose electricity is at least partly by fossil gas, coal or oil.
This is certainly the case for most American households: While the grill mix is improve, it’s still far from clean. In 2023, renewables provided just 21 percent of U.S. electricity generation, with carbon-free nuclear power coming in at 19 percent. The other 60 percent of power came from burning fossil fuels.
So do electric heat pumps really lower emissions if they run on dirty grid power?
The answer is a clear yes. Even on a carbon-heavy diet, heat pumps eliminate tons of emissions annually compared to other heating systems.
The latest study to hammer this point home was published in Joule last month by the National Renewable Energy Laboratory. The team modeled the entire US home stock and found that over the appliance’s expected lifetime of 16 years, switching to a heat pump heater/AC reduces emissions in each of the contiguous 48 states.
In fact, heat pumps reduce carbon pollution, even if the process of cleaning up the U.S. grid moves more slowly than experts expect. The NREL team used six different future scenarios for the grid, ranging from aggressive decarbonisation (95 percent carbon-free electricity by 2035) to sluggish (only 50 percent carbon-free electricity by 2035, in the event that renewables end up costing more than their current trajectories are predicted). They found that, depending on the scenario and level of efficiency, heat pumps reduce household annual energy emissions by an average of 36 percent to 64 percent—or 2.5 to 4.4 metric tons of CO22 equivalent per year per housing unit.
This is a staggering amount of emissions. For context, prevention of 2.5 metric tons of CO2 emissions is equivalent to not burning 2,800 pounds of coal. Or not driving for half a year. Or switch to a vegan diet for 14 months. And at the high end of the study’s range, 4.4 metric tons of CO2 is almost equivalent to the emissions of a return flight from New York City to Tokyo (4.6 metric tons).
Eric Wilson, senior research engineer at NREL and lead author of the study, told me, “I often hear people say, ‘Oh, you have to wait to put in a heat pump because the grill is still dirty.'” But that. is so. faulty logic. “It’s better to switch now rather than later – and not lock in another 20 years of a gas furnace or boiler.”
Emissions savings tend to be higher in states with colder winters and heaters that run on fuel oil, such as Maine, according to the study. (Maine seems to be one step ahead of the researchers: heat pumps are so popular there that the state already blew past its heat pump adoption goal two years ahead of schedule.)
A dirty grill therefore does not cancel out a heat pump’s climate benefits. But heat pumps can generate emissions the same way standard ACs do: by leaking refrigerant, the chemicals that enable these devices to move heat. Even if it is orphan phased outthe HVAC standard refrigerant is R-410A 2,088 times more powerful a greenhouse gas than CO2so even small leaks have a big impact.
However, additional emissions from heat pump refrigerant leaks hardly make a dent, given the emissions heat pumps avoid, the NREL team found. Typical leakage rates of R-410A increase emissions by only 0.07 metric tons of CO2 on average2 equivalent per year, shaving just 3 percent off the overall savings of 2.5 metric tons, Wilson said.
A 2023 analysis from climate think tank RMI further supports heat pumps’ climate bona fides. Across the 48 continental states, RMI has found that replacing a gas furnace with an efficient heat pump saves emissions not only cumulatively over the appliance’s lifetime, but also in the very first year it is installed. RMI estimated that emissions prevented in that first year were 13 percent to 72 percent relative to gas furnace emissions, depending on the state. (Canary Media is an independent affiliate of RMI.)
Both the RMI and NREL studies focused on air-source heat pumps, which draw heat from the outdoors in cold weather and can be three to four times as efficient as gas furnaces. But ground-source heat pumps can be more than five times as efficient as gas furnaces — unlocking even greater greenhouse gas reductions, according to RMI.
How much can switch to a heat pump lower your home carbon emissions? For a high-level estimate, NREL put out an interactive dashboard. In the “states” tab, you can filter down to your state, building type and heating fuel. For example, based on a moderate grid decarbonization scenario in my state of Colorado, a single-family home that swaps out a gas furnace for a heat pump could reduce emissions by a whopping 6 metric tons of CO2.2.
You can also get an estimate from Rewiring America’s personal electrification plannerwhich uses more specific information about your home, or ask an energy auditor or whole house decarbonization company if they can calculate 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 were to switch to heat pump heating right now, emissions from the entire US economy would shrink by 5 percent to 9 percent. That’s how powerful a decarbonizer heat pumps are.
