Turning the heating on has never been so controversial. Not only is it costing us more, but residential heating accounts for around 14 per cent of the UK’s greenhouse gas emissions and cleaning up the sector has been painfully slow.
The government plans to be installing heat pumps in 600,000 homes every year by 2028. These numbers might seem like a bit of a stretch considering annual installations currently sit at around 40,000 and there is already a shortfall in the number of installers. Is a fifteen-fold increase in five years realistic?
Well, the incentives to make the switch are starting to ramp up. Over the last two years we have witnessed the publication of flagship legislation to encourage heat pump uptake - this includes £5,000-£6,000 grants for homeowners towards the cost of installing a heat pump, as well as an effective ban of the humble gas boiler in new build properties from 2025 (2024 in Scotland).
It is likely then that in the coming years we see an increasing number of people rip out their combis and make the switch to cleaner heat. Any difficulties will likely come down to cost; It’s a matter of economics - the science is important too. Here’s what you need to know.
What is a heat pump?
A heat pump is an electric-powered heating system which can replace the traditional role of fossil fuels in heating our homes. It utilises heat from the air outside rather than burning a flammable fuel. The most common of these is the air source heat pump. Air source heat pumps are usually about the size of a dishwasher and are installed directly outside of a property - this external unit looks, slightly underwhelmingly, like a large air conditioning unit.
How do they work?
So how does ambient air from outside produce heat? While it might not seem like there is much warmth to be gained from the seemingly-arctic air in the middle of a UK winter, heat pumps can efficiently absorb any available heat into a refrigerant fluid, which has a very low boiling point. This fluid circulates through the heat pump unit, with the fan in the heat pump blowing the outside air onto the refrigerant. The refrigerant naturally absorbs heat from the air and quickly turns it into a gas.
Still with me? This gas is then compressed which raises the temperature higher still, turning it into a superheated vapour. This superheated vapour then enters a plate heat exchanger where it encounters the water from your central heating system. The heat is transferred from the superheated refrigerant to the water, the water travels on to the radiators in the home and the refrigerant passes back through an expansion valve, losing its remaining pressure and heat in the process and getting ready to repeat the cycle all over again.
Are they better for the environment?
Unlike conventional forms of home heating - gas, oil, and LPG - heat pumps involve no direct burning of fossil fuels and, like an electric vehicle, produce no CO2 emissions at the point of use. The pump is powered by electricity but the heat generated is four times the amount of electricity used in the process.
They do, of course, require electricity and are therefore only as clean as the grid that powers them (provided you don’t have solar panels). The good news here is that CO2 intensity of UK electricity generation has roughly halved over the last twenty years due to the phase-out of coal.
Getting to the numbers then, an average heat pump in the UK emits approximately 1.6 tonnes of CO2 per year. By comparison, a gas boiler produces about 3.7 tonnes in the same period and an oil boiler is even higher at around 5.3 tonnes.
On top of this, a much-overlooked issue is gas boilers’ contribution to air pollution. Our boilers produce eight times as much nitrogen dioxide as the UK’s gas power plants, an air pollutant linked to health complications.
In summary, heat pumps hold a lot of promise when thinking about decarbonising our homes, but there are challenges to unpick before we start hitting the numbers set by the government. Look out for my next article if you’d like to learn more about whether your home is ready to make the switch.
