Heat pumps have existed for decades as energy-efficient heating systems. So why are they all over the news right now, and why are they so expensive? This post summarizes the major factors concerning this promising piece of low-carbon infrastructure and the role it could play in decarbonizing buildings.
Unlike other heating devices, such as furnaces that produce heat through the combustion of fossil fuels, heat pumps exchange heat from one space to another. There are different kinds of heat pumps, including ground-source and water-source geothermal, as well as ducted and ductless air-source heat pumps. Here we focus on air-source heat pumps, which are the most common type in residential buildings in the United States.
As the Energy Star graphic in Figure 1 depicts below, air-source heat pumps use a refrigerant to absorb heat from outside air and release it into an indoor space. Although heat pumps are thought of as novel technology, typical air conditioning units use a similar principle to move heat in the opposite direction from inside the home to outside. However, heat pumps are more versatile than air conditioners: when equipped with a reversing valve, a heat pump can both cool and heat a room or building.
The most commonly used refrigerants are hydrofluorocarbons (HFCs), which can leak out of the heat pump and into the atmosphere. Although powerful greenhouse gases, HFCs account for only 2-5% of the lifetime total warming impact of heat pump systems, and there are efforts underway to reduce these refrigerant emissions: In May 2022, the International Electrotechnical Commission approved an update to standards that would transition away from HFCs to more climate-friendly refrigerants in air conditioners and heat pumps.
Air-source heat pumps have been around for several decades but have mostly been used as a heating solution in temperate climates. However, the technology has significantly improved, and heat pumps can now be used in temperatures as low as -13 degrees Fahrenheit, which is sufficient to heat a Pacific Northwest winter cold snap.
Rising temperatures due to climate change and experiences such as the heat dome that hovered over the Northwest during the summer of 2021 suggest Northwesterners may be wise to install heat pump units that provide both heating and cooling in homes where central air conditioning has historically not been necessary.
Heat pumps are significantly more efficient than alternative heating methods because they do not convert energy into heat but rather use electricity to transfer heat. Even compared to other electric heating systems, heat pumps win out: they use half the electricity of electric furnaces and baseboard heaters. Compared to gas furnaces, heat pumps can use three to four times less energy, making it even more efficient to use natural gas-generated electricity to power a heat pump than to use natural gas directly in a gas furnace.
In addition to massive benefits from energy efficiency, heat pumps reduce overall emissions, especially in places with access to cleaner electricity such as the Pacific Northwest. An Energy Policy study published in April 2022 found that residential heat pumps reduce carbon dioxide emissions by 38–58% compared to gas furnaces. The range depends on location, factoring in climate and energy resources used for electricity production.
Recently, scientists also pointed to the public health risks associated with gas appliances. While the worst offenders for impacting indoor air quality are gas-powered stoves and ovens, emissions from gas-fueled furnaces and water heaters that vent outdoors also impact outdoor air quality and can pose a danger to inside air when their gases draft into the home.
There are now compelling geopolitical reasons for the world to cut its reliance on oil. Bill McKibben argues in Heat Pumps for Peace and Freedom that American manufacturers should start producing electric heat pumps in large quantities to ship to Europe as European Union nations strive to cut their dependence on Russia for natural gas in the wake of that country’s invasion of Ukraine.
Finally, despite high up-front costs to install, the high energy efficiency of heat pumps provides cost savings in the long run. Exact savings vary based on the size and location of the home, how insulated and therefore energy efficient it is, and the current heating system. A 2021 analysis by Carbon Switch, using data from the National Renewable Energy Laboratory, found that homeowners can save anywhere from $100 to $1,300 annually by switching to a heat pump.
One of the biggest drawbacks to heat pump installation is significant upfront installation costs for home previously heated by gas. Gas, electric, and oil furnaces cost between $1,500-$9,500 on average in the U.S. While costs vary depending on the home and location, the cost in the U.S. for a standard heat pump unit and installation is between $3,500-$20,000, with an average cost of about $14,000 after rebates. Cost factors for heat pumps include home size; number of zones (if installing mini-splits units that heat individual zones of the home); location; new construction vs. retrofits, and available incentives.
Part of the reason that heat pumps remain so expensive in the U.S. is that the supply chain and workforce are not yet developed at scale. There is a bit of a chicken and egg problem: installers don’t have heat pumps in stock because there isn’t enough demand, and manufacturers are hesitant to invest in heat pumps because they don’t know if the market is there.
History should also not be underestimated as a barrier to heat pump adoption. Many people remember days when heat pumps were only viable solutions for warm climates. There are efficient cold climate heat pumps today, but a 2019 Columbia University study found that air source heat pumps are still most cost competitive in places where electricity is inexpensive, such as the Pacific Northwest, and the climate is mild.
The study also noted that by the mid-2030s, air source heat pumps will be the lowest-cost option for typical residential buildings across the U.S., including cold climates, due to “climate policies consistent with rapid decarbonization” and technological advances. However, today they are not the cheapest option, and cost remains a barrier for many home and building owners.
Lastly, many people simply don’t know about the benefits of heat pumps. Since most heating replacements happen when a heating or cooling system breaks, homeowners are more likely to choose the quickest, easiest option and may not have time to spend doing research. Even if they do request a heat pump, contractors are not always familiar or comfortable with heat pump technology, and therefore may not offer them as an option.
Heat pumps are a crucial strategy for decreasing emissions from the building sector. The necessary technology exists, and we now need policy and market shifts to promote rapid and affordable heat pump adoption at the pace necessary to meet our climate goals.
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