For as long as air conditioning has been widely available in the United States, residential electrical loads have peaked in the summer. Electric utilities have built business models and developed capacity plans based on this schedule. 

As natural gas has become the dominant source for electricity generation, this regular cycle has benefited that fuel’s producers, providing a warm-weather market for a resource that typically has its own peak in winter.

But times are changing with the current drive to electrify home heating while replacing natural gas electricity generation with solar, wind and other renewable resources. In many regions, these moves will push peak demand into winter’s coldest months. And, unless renewable supplies—and the wires needed to ship that power to U.S. homes—grow substantially, we could just be trading gas used to make heat for gas used to fire up electric generators in the move to furnaces that don’t use fossil fuels.

Heating’s climate impact

While heating and cooling needs obviously vary by region, nationally, they are responsible for 38% of total U.S. residential emissions, according to the U.S. Energy Information Administration. A lot of those emissions are due to the popularity of natural gas as a heating fuel—it’s the primary choice in 47% of the nation’s homes, according to the U.S. Census Bureau, with propane tacking on an additional 5% and oil another 4%. However, these figures also vary widely, with natural gas heating 70% of Midwestern homes and only 35% in the South, where electric resistance heating predominates.

But new electric air source heat pumps (ASHPs) that work well in all but the coldest environments and provide cooling in the summer are beginning to make inroads, outselling traditional natural gas furnaces for the first time in 2022. Climate advocates say this trend is important for reducing emissions related to heating through the entire natural gas extraction and delivery supply chain.

“Natural gas doesn’t magically come out of the ground, it comes from all the oil and gas extraction processes,” said Jonathan Buonocore, assistant professor of environmental health at Boston University’s School of Public Health and lead author of a 2022 study, “Inefficient Building Electrification Risks Prolonging Fossil Fuels.” 

He added that leaks of methane­—a significant greenhouse gas and the prime component in natural gas­­—at drilling sites and along pipelines pose significant health risks along with climate challenges. 

“There are a lot of impacts from the whole production process that lead to deaths downwind and a large amount of asthma attacks occurring throughout the country,” Buonocore said.

U.S. ASHP adoption began in southern states, where most homes are already wired for electric heat, primarily through inefficient baseboard resistance units. There, homeowners also value the equipment’s ability to supply cooling more efficiently than traditional air conditioning units. Manufacturers have beefed up performance, making heat pumps a solid choice in significantly colder climates, too. For example, recent surveys of heat pump owners by Efficiency Maine, the state’s lead energy-efficiency agency, found 93% of homeowners rated their experience with the equipment as 9 or 10 on a zero-to-ten scale.

Buonocore and his research colleagues modeled how a large-scale move to electric heating could shift current demand patterns by analyzing U.S. building energy data between March 2010 and February 2020. By converting the British thermal units used to measure natural gas into kilowatt-hours, they were able to better understand total heating-­energy demand in electrical terms. 

They found that winter heating demand drives overall energy consumption across all sources to its highest levels in December and January, with a secondary peak related to cooling in July and August. Their study also found that meeting these needs with electricity alone, using only ASHPs, could prove challenging. Incorporating more efficient individual or networked ground source heat pumps would help reduce winter peaks, however, and require a less substantial renewable energy buildout to meet those needs with electricity alone.

For comparison, the team looked at how systems with a higher coefficiency of performance (COP) rating could reduce new generating needs. COP measurements define how many units of heat are produced for each unit of electricity. Electric baseboard systems typically score a COP of one or less, while ASHP COPs generally fall between two and four and those for GSHPs range between three and five. The researchers found that simply moving everyone to equipment with a COP of one, powered solely by renewables, would require increasing current January wind production by 28 times, or boosting solar by 303 times during the same period.

The report makes clear that these demand predictions are theoretical and don’t reflect how heat pump performance can shift with the seasons or how strategies such as storage could help utilities address the demand changes. However, it does illustrate how important heating equipment efficiency will be for moderating that demand and the carbon-free capacity that will be required to meet it.

Texas-sized savings

Of course, the effects of a shift to winter demand peaks will vary by state and region, and planners are beginning to get a better handle on what a shift to 100% electric heating might mean for their locations. 

Texas has become a focus in these efforts for several reasons—for one, it’s the nation’s largest electricity producer, and it’s almost entirely isolated from the rest of the North American grid. It’s also gone big into wind and solar. It is the nation’s top wind-energy producer and ranked second in solar production after California. About 60% of the state’s residential customers use electricity to meet their heating and cooling needs, which prompted Philip White, now a research engineer in the Residential Buildings Solutions and Scalings Group at the National Renewable Energy Laboratory (NREL), to focus his doctoral thesis work on what would happen if the remaining 40% of Texans switched from natural gas to electricity to condition their homes and apartments.

White was lead author of a 2021 paper, “Quantifying the impact of residential space heating electrification on the Texas grid,” documenting this work while a student at the University of Texas at Austin. He completed his research before the “Great Texas Freeze” of February 2021 put a spotlight on the state’s challenges in meeting demand surges during severe winter weather. Instead, the research team used weather and demand data from 2016, along with NREL software, to model that year’s electricity use for each of the 17 regions within the boundaries of its primary system operator, the Electric Reliability Council of Texas (ERCOT). 

Researchers in New York City are concerned about recent mandates aimed at entirely eliminating fossil fuels from the city’s enormous building portfolio.

Texas’ residential-sector winter demand peaks could climb by as much as 36%, or 12 gigawatts (GW), the researchers found, forcing ERCOT to add up to 10 GW of new capacity (a 25% boost for this customer group). Interestingly, even with the winter increases, total annual demand would remain flat or even decrease because updated heat pumps would be more efficient than the aging air conditioning equipment they’d replace.

“The increase in demand we saw was with the fuel-switching houses—meaning we’re switching the heating fuel of the home from natural gas and propane to electricity, via the heat pump,” White said.

But, he added, while those fuel switchers will eventually force the Texas renewables market to get even bigger, ERCOT has some time to meet those needs.

“The change is incremental—it’s not like what happened in our paper will happen overnight,” he said. “Furnaces last probably between 15 and 30 years, and then the consumer is going to make a choice of what kind of system to replace their furnace with.”

Big switch in the Big Apple

While White’s work in Texas focused on the effect of consumer heating-­system choices, researchers in New York City are concerned about recent mandates aimed at entirely eliminating fossil fuels from the city’s enormous building portfolio. Urban Green Council, an environmental nonprofit dedicated to decarbonizing the city’s buildings, looked at whether the grid there could handle the electrification required by two laws designed to cap and reduce buildings’ greenhouse gas emissions and phase out the use of fossil fuel-fired equipment in new construction. These laws will have the effect of fully electrifying the city’s buildings over the next several decades, with a goal of hitting net-zero performance by 2050.

Midea’s winning entry in NYCHA’s heat pump competition straddles the lower sill of a window and runs on standard 120V/15A circuits. Photo by Midea.

“We will never get to our climate goals using fossil fuels, full-stop—in New York City, our number-one source of carbon comes from furnaces, boilers and hot water heaters,” said John Mandyck, Urban Green’s CEO. “It’s 40% of our total citywide emissions, so we have to transition to a different technology that plugs into a renewable grid.”

As a proponent of the new regulations, which used language from their recommendations, Urban Green wanted to understand how New York’s grid would handle full electrification of heating. Their 2021 review, published in the report “Grid Ready: Powering NYC’s All-Electric Buildings,” found that the city’s peak electricity demand period would, indeed, switch from summer to winter, but that the combination of existing capacity and a lengthy transition period will help ensure the ability of ConEd, the local utility, to keep up with the changes.

“We found there’s a 42% differential between the winter and the summer—our grid is built out for the hottest day of the year,” Mandyck said. “So, we have 42% headroom to plug stuff into the grid in the winter, before we get to the summer peak. Over time, the winter will eclipse the summer in demand, but this is a multidecade phenomenon.”

New, window-mounted heat pumps are one of the tools the New York City Housing Authority (NYCHA) is testing out to help meet net-zero goals. Two manufacturers, Midea and Gradient, developed winning entries in the competition. They will be tested this winter, and if all goes well, an initial installation of 30,000 could begin soon.

Header image: Getty images / Bangon Pitipong