Homes in many areas of the U.S. weather the summer heat largely without central air conditioning. But little by little, rising temperatures has made that more and more untenable — leaving many households facing a challenge, but also an opportunity.

Rewiring America analyzed housing and temperature data to identify the areas of the country experiencing warming temperatures of more than two degrees Fahrenheit, where there are also a high percentage of residents living without central air.

What we found in each location is that heat pumps can fill the void — doing double duty in providing cooling in the hot months, and heat during cold months. All that without adding to the pollution that’s increasing the need for air conditioning in the first place.

The U.S. Environmental Protection Agency has dedicated $450 million to support heat pump adoption in Connecticut, Maine, Massachusetts, New Hampshire, and Rhode Island — states that are among our top 10 for experiencing a rise of more than than two degree Fahrenheit and having a majority of residents without central air.

Other states across the country also face the same challenge. 

In North Dakota — the first on the list — more than a third of its households (68 percent) face a greater than two degree increase in temperature while also lacking central air.

In second place: Maine  — where 61 percent of households lack central AC. 

Maine is tackling the issue head-on: by becoming the nation’s leading installer of heat pumps and heat pump water heaters. They’ve installed more than 100,000 heat pumps in 2023 alone, two years ahead of a state deadline. 

Here are the top states where heat pumps could be the solution to this problem:

How we did it:

To arrive at the top 10 states ranking, we pulled housing data from the National Renewable Energy Laboratory’s (NREL) Resstock data, Restock 2022.1 version — which offers a detailed model of the types of housing located all over the country, including what type of heating and cooling systems they have, how old they are, and how much energy they tend to consume. We took the number of homes that lacked central air, located in areas where the rate of temperature increase was more than 2 degrees Fahrenheit, and divided that number by the total number of households in the state.

To build the maps, we pulled climate data from the Environmental Protection Agency and the National Oceanic and Atmospheric Administration that showed the rate of temperature change across the U.S. from 1901 to 2021. We used a heat map range of colors from tan to dark red to show the areas of the country where the temperature rose between zero to 3.5 degrees Fahrenheit per century. 

Next, we used the Department of Energy National Renewable Energy Laboratory’s (NREL) Resstock data to identify locations in the U.S. where more than half of a county lacks central AC. (fig.2).

From there, we filtered our climate map to only display areas where the temperature rose two degrees Fahrenheit per century or greater — which is a sign that they’re warming more rapidly than other parts of the U.S. 

We then overlaid our heat map with the layer showing the counties where a majority doesn’t have AC (fig.3). 

In our final map, we color-coded the overall rate of temperature change in each of the areas lacking central air. This map highlights in dark purple the areas of the country that are warming more rapidly and where a majority doesn't have central AC (fig.4). These highlighted counties are ideal places to install heat pumps.