Heat pumps have moved from a niche technology to a centrepiece of plans to cut household emissions. They are also widely misunderstood. Here is a clear, jargon-light explanation of what they are, how they work, and whether one makes sense for your home.

The core idea: moving heat, not making it

A traditional boiler or furnace creates heat by burning fuel. A heat pump moves heat that already exists from one place to another, using electricity to do the moving.

That distinction is the whole story, because moving heat is far more efficient than creating it. A good gas boiler converts most of the energy in the fuel into heat — call it 90 percent. A heat pump can deliver three to four units of heat for every unit of electricity it uses, because most of the heat is harvested from the environment rather than generated.

Engineers express this as the coefficient of performance (COP). A COP of 3.5 means 3.5 units of heat out for one unit of electricity in — an effective "efficiency" of 350 percent, which is impossible for any device that burns fuel.

How the cycle works

A heat pump relies on a simple physical fact: when a fluid evaporates it absorbs heat, and when it condenses it releases heat. Inside the unit, a refrigerant cycles continuously:

  1. Cold refrigerant passes through an outdoor coil and absorbs heat from the outside air or ground — even cold air contains usable heat.
  2. A compressor squeezes the refrigerant, raising its temperature sharply.
  3. The hot refrigerant passes through an indoor coil and releases its heat into your home.
  4. The refrigerant expands, cools, and the cycle repeats.

It is the same mechanism as a refrigerator, which moves heat out of its insulated box. A heat pump simply does this for a whole building — and can run in reverse to provide cooling in summer.

The cold-weather myth

The most persistent misconception is that heat pumps do not work in the cold. They do. Cold-climate heat pumps are designed to extract heat at temperatures well below freezing, and they are standard in some of the coldest inhabited regions on Earth.

It is true that efficiency falls as the outside temperature drops, because there is less heat to harvest and the pump works harder. But "less efficient" is not "stops working." Modern variable-speed units maintain useful output far below the point where older models struggled.

A heat pump in winter is not fighting the cold by brute force. It is quietly concentrating the diffuse heat that is in the outdoor air, even when that air feels frigid to us.

Types of heat pump

  • Air-source. Draws heat from outside air. The most common and lowest-cost to install.
  • Ground-source (geothermal). Draws heat from the ground, which stays at a stable temperature year-round. More efficient and more expensive to install, since it requires buried pipework.
  • Air-to-water. Feeds heat into a wet central-heating system (radiators or underfloor) and hot water. Common where homes use radiators.
  • Air-to-air. Delivers heat (and cooling) directly as warm or cool air, like a ductless mini-split.

Are they worth it?

The honest answer is usually, with caveats.

The case for:

  • Lower energy use. Far more heat per unit of energy than combustion.
  • Lower emissions, especially as electricity grids add more renewables. A heat pump on a clean grid is a genuinely low-carbon way to heat a home.
  • One system for heating and cooling.
  • Incentives. Many governments offer grants or tax credits that offset the higher upfront cost.

The case for caution:

  • Higher upfront cost than a like-for-like boiler replacement.
  • Running-cost depends on local prices. Where electricity is expensive relative to gas, savings shrink.
  • Best paired with a well-insulated home. Heat pumps deliver heat at a lower, steadier temperature, so draughty, poorly insulated homes benefit from insulation upgrades first.

The bottom line

A heat pump is not a gimmick — it is a mature, efficient technology that moves heat instead of burning fuel, and it can both warm and cool your home. Whether it pays off depends on your climate, your home's insulation, local energy prices and available incentives. For many households, especially those upgrading insulation anyway or replacing an ageing system, it is the most efficient option available.