Heat pumps have become the technology of choice for keeping homes warm, but what are they and how do they work?
Few climate technologies have had the momentum that heat pumps have today.
While the share of electric vehicle and induction cooker sales may be growing, they still account for a small percentage of all car and cooker sales, respectively. However, in the past year, heat pump sales in the US have surpassed gas-fired ovens as the technology of choice for comfort in homes.
The sudden rise in popularity of heat pumps might make you wonder: what exactly are they, how do they work, and are there any incentives that can help keep prices down?
Calling it a “heat pump” might be a bit of a misnomer. This is because the heat pump heats and cools your home according to the season. To do this, they use electricity instead of methane gas, reducing harmful greenhouse gas emissions and protecting the health and safety of the population.
“Sounds amazing,” says Vince Romanin, founder of window heat pump startup Gradient. Spoiler: it’s just physics.
The short answer is that they work by moving heat from one place to another. This is actually what an air conditioner does: it draws heat out of your home and draws in cold air. If you’ve ever stood outside next to an air conditioner, you’ve felt the heat being pushed out. A heat pump can do the same in the summer, but it also has the ability to reverse the process in the winter, drawing heat from outside into your home. Some heat pumps, called ground source heat pumps, use the ground outside the home as a place to absorb or reject heat.
In many cases, yes. They are much more efficient. It’s much easier to move heat around than it is to generate heat from scratch by igniting a gas and then fanning the resulting heat. Romanin notes that heat pumps are 300 percent more efficient than gas stoves.
“Burning thousands of degrees of fossil fuel to heat an apartment 10 or 20 degrees is absurd. This is a crime against the laws of thermodynamics,” he said.
This efficiency can lead to cost savings. A Carbon Switch analysis found that switching from a gas stove to a heat pump could save the average American household $557 a year on their energy bills.
In addition to being efficient, it’s also safer to have natural gas delivered to your home on an occasional basis due to a number of public health and safety implications. Ventilation systems that are not properly installed or maintained can allow contaminants to enter your home. In this case, there is a risk of transferring flammable materials to the basement and igniting there.
We haven’t even got the climate benefits yet. A study published last year found that replacing a gas stove with a heat pump could cut carbon emissions by 53 percent in every US household. Meanwhile, a carbon shift analysis showed that household emissions would be reduced by 142 million metric tons.
The conventional wisdom is that air source heat pumps do not perform well in cold weather because it is difficult to extract heat from very cold air. Some systems also use an energy intensive form of heating to prevent freezing, reducing efficiency. Geothermal heat pumps work more easily because the ground temperature remains fairly constant.
But “it’s amazing what manufacturers and universities are capable of,” says Subhrajit Chakraborty, research and development engineer at UC Davis’ Western Cooling Efficiency Center.
Air source heat pumps have become more efficient at capturing heat, even when outside temperatures are below freezing. This year, Energy Star, the US government’s program to promote energy efficient appliances, introduced cold climate ratings for heat pumps. A database maintained by the nonprofit Northeast Energy Efficiency Partnerships shows over 1,400 models qualify.
Real-life testing in cold climates from Maine to Minnesota has shown that heat pumps can handle the harshest winter conditions.
They are not too cheap. Installing a heat pump in the US is a four- or five-figure investment, depending on home size, climate, and other factors. Air source heat pumps are generally less expensive than geothermal ones, but Chakraborty said the increased efficiency of ground source heat pumps could make them more cost-effective for 15 years or more.
have. In the US, the Inflation Reduction Act provides tax credits of up to 30% on the cost of a $2,000 (about £1,700) heat pump. The law is more generous to families whose income is less than 80% of the area’s average. It will cover 100% of the initial costs of buying and installing a heat pump up to $8,000 (about £6,700). Many states also offer discounts. Together, these benefits can help make heat pumps affordable for everyone, not just the wealthy who have traditionally purchased them.
In the UK, the government is offering homeowners up to £6,000 ($7,150) to install heat pumps. The urgency to install additional heat pumps has risen since the war in Ukraine, but as of last month, a third of the £6.6bn ($7.8bn) proposed by the government for energy efficiency remained unspent.
Some state and federal governments in Australia are offering incentives for heat pump water heaters, a related technology that heats water rather than a space.
First, not everyone lives in a separate house. Residents of apartment buildings have several options. However, Gradient and a growing number of US HVAC companies are looking to change that with window heat pumps.
The Gradient model is a stylish device that sits like a saddle on the windowsill and does not require professional installation. This works for more temperate climates, although Romanin said models for colder climates are being developed. But the company and Midea America plan to launch a pilot project in New York City public housing this year, installing window heat pumps that can operate at cooler temperatures, as part of a $70 million HVAC upgrade.
Installing a heat pump and electrifying other appliances can also require homeowners to upgrade their electrical panels, adding $1,300 to $3,000 to any project. (In the US, the IRA provides a $600 tax credit on these upgrades when done with other electrification upgrades.)
Chakraborty’s team is working on a multifunctional heat pump that can be used for space heating and hot water.
According to Romanin, new refrigerants for heat pumps are also entering the market. Hydrofluorocarbons, one of the most common refrigerants in use today, are also extremely potent greenhouse gases. They have become commonplace because they have replaced the ozone depleting refrigerant CFC. Currently, HFCs are on the verge of being phased out, but “if we don’t pay attention to what we replace them with, we risk repeating the same mistakes,” says Romanin.
Gradient uses a relatively low impact HFC called R32. But “it’s a stepping stone for us” as the company looks for better options, he said.