What are heat pumps and how do they work?

This article was first published in August 2022 and updated in November 2023 to include recent data.

As the energy crisis sends the cost of heating and air conditioning through the roof, you might be wondering if heat pumps are the answer.

They are pricey, but heat pumps promise to bring down energy bills and deliver savings in the end. And because they don’t emit carbon dioxide, they could also be better for the planet.

So how do they work?

There are 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 out there in the air or the ground. Heat pumps are designed to get 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 cold 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 has reversed the natural flow of the heat and moved 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.

You could easily be looking at a bill of more than $10,000 to buy and install any sort of heat pump, so it is not a cheap option in the short term. But 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 down in the summer, it simply goes into reverse. A heat pump in cooling mode should also lower the humidity in a house, which can make it a lot 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 were capable of cooling 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.

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 to the energy crisis and the journey to net zero. In the World Economic Forum's 2023 report, Fostering Effective Energy Transition, heat pumps are very much included in the list of solutions to tackle the "triple planetary crisis of climate change, pollution and biodiversity loss".

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.”