What are heat pumps and why are they gaining in popularity?

This article has been updated in January 2025.

As the energy crisis continues to raise the cost of heating and air conditioning, heat pumps are becoming increasingly popular.

Although they can be pricey, heat pumps promise to reduce energy bills and ultimately deliver savings. Experts argue that because they reduce carbon dioxide emissions, they are also better for the planet.

So how do they work?

Two things to remember: first, no matter how cold it is outside—even if the temperature drops well below zero—there is always some thermal energy in the air or the ground. Heat pumps are designed to bring enough of it into your home to warm you up.

The second thing is, left to its own devices, heat always moves from a warmer place to a colder place – which is why houses get chilly in winter. A heat pump takes control of that natural heat exchange process so you can either cool down or warm up your home.

It can do that because it contains a liquid refrigerant in a copper coil. This absorbs heat from the air outside, and then the pump uses electrical power to compress the refrigerant, increasing its temperature. That transfers the heat indoors.

The heat pump reverses the natural flow of heat and moves the energy available in a colder place (outside) to a warmer one (a house). It works on the same principle as a refrigerator.

In fact, US inventor Robert C. Webber came up with the idea in the 1940s when he accidentally burnt his hands on the outlet pipes of his deep freezer. Webber connected the pipes to a prototype heating system at his house, and the heat pump was born.

While air-source heat pumps get their warmth from the earth, ground-source systems draw it from the earth. They tend to be more expensive.

Buying and installing a heat pump can cost more than $10,000, so it is not a cheap option in the short term. However, because they are designed to use less energy than the heat they generate, heat pumps should be an efficient way to heat your home.

Depending on the exact system, it will either heat the air indoors with fans, or be used to warm up radiators or underfloor heating.

If you want to use an air-source heat pump to cool your home in the summer, it simply switches to reverse. A heat pump in cooling mode should also lower the humidity in a house, which can make it much more comfortable.

There is a big demand for the technology in parts of the US where air conditioning is uncommon, but where people are now having to deal with more severe heatwaves because of climate change, Bloomberg reports.

One study from clean energy non-profit RMI modelled the performance of different cooling options in Seattle during a record-breaking heatwave in June 2021. Researchers found heat pumps could cool homes in extreme temperatures and cost $228 less per year than having separate air conditioning and heating systems.

The same study said CO2 emissions were cut by around a quarter for the entire home.

These are important savings, not least because the US now experiences an extreme weather event costing the economy over $1 billion every three weeks – compared to every four months in the 1980s – according to the country's National Climate Assessment.

But it's a myth that heat pumps are mainly useful in hot weather situations. Sweden, Finland and Norway not only have the coldest climates in Europe, but they also have the highest heat pump sales per 1,000 households across the continent, reports Carbon Brief. Meanwhile, Germany and the UK are lagging behind in heat pump adoption, despite government subsidies to encourage greater take-up.

The consumer journal Which? points out that because heat pumps use electric power, they are not zero carbon unless the electricity comes from renewable sources like solar or wind.

But they are being seen as part of the answer for the journey to net zero. Indeed, heat pump sales saw "huge growth" during the peak of the energy crisis, according to the World Economic Forum's 2024 report, Fostering Effective Energy Transition, and now "represent the most-deployed home heating solution, overtaking fossil fuel-based systems in a number of countries".

Alexander Gard-Murray, a climate change researcher and economist at Brown University, told the Washington Post: “It’s a home comfort issue. It’s a climate issue. It’s a security issue. Any one of them would be enough to move aggressively on heat pumps, but taken together I think the evidence is insurmountable.”