Heat Pumps

Heat pumps started becoming mainstream in the last decade or so but their uptake has been limited in the UK. They work differently to boilers in that they extract heat from the surroundings rather than by burning fuel.

Heat pumps work by compressing and expanding a refrigerant vapour. Expanding the refrigerant causes its temperature to drop. It’s then pumped through a heat exchanger outside the house where it is warmed up by the environment. This can be above ground in an air-source heat pump or buried underground in a ground-source heat pump. The warmed refrigerant is then compressed again, causing its temperature to increase, and this hot refrigerant is used to warm the water for the heating system.

Heat pump schematic

Heat pumps are extremely efficient, delivering up to three times as much heat energy as they use in electricity. This makes them an appealing option, but there are several things to consider before you take the plunge –

  • Heat pumps work at lower temperatures than gas central heating (typically 50-60°C rather than 60-70°C). This means you may not get enough heat out of your existing radiator-based central heating system if you switch to a heat pump supply. In new builds, heat pump systems typically use underfloor heating which is better-suited to low temperature operation, but it would be very expensive to retrofit an entire house with underfloor heating.

  • Although heat pumps only use one third of the energy of a gas boiler, they use electricity which is roughly three times more expensive than gas per kWh. Therefore you won’t actually save any money on your bills despite the significant financial investment.

  • Electricity has roughly the same embodied carbon per kWh as gas (remember it is still mostly generated from fossil fuels). Therefore, although you may be reducing your energy usage by 66% there will still be some associated carbon emissions. This is still a positive step and will make your home “Net Zero ready” by using electricity, but we'd wager that this incentive alone is not enough to justify the cost for most people, especially as you could save a similar amount of carbon for less money using other measures from this website.

In our view upgrading to a heat pump heating system is probably only cost-effective if you’re undertaking a major refurbishment and are replacing your entire heating system including radiators. Otherwise the cost and disruption of the installation make them unappealing compared with other energy saving measures. You will certainly get a better return on investment from installing more insulation or replacing an older gas boiler with a new, high-efficiency one.

However, that’s not to say heat pumps don’t have a place in the our energy strategy. The UK has already halved carbon emissions from its power generation since 1990. As we approach 2050 we can expect an increasing proportion of our electricity to be generated from renewable and low-carbon sources such as wind, solar and nuclear. In the future, with cheap “green” electricity, heat pumps will inevitably overtake gas boilers as the cheapest and most environmentally-friendly option. We’re not there yet, but it certainly makes sense for heat pumps to be installed in new build properties to ensure these are “future proof”.