Retrofitting a low-carbon heat pump into an existing property – what’s involved exactly?

As energy bills rocket, more and more homeowners are looking into alternative ways to heat their homes this winter. Swapping a boiler for an air source heat pump will protect families from global price spikes in oil and gas.  At the same time, households are being offered £5,000 grants to replace boilers with heat pumps that run on electricity under plans to tackle climate change.

How do heat pumps work?

An air source heat pump looks like an air conditioning unit and works a bit like a fridge in reverse. It uses electricity to absorb heat from the outside air and increases it to a higher temperature using a compressor. The pump then transfers the heat to the central heating system in your home. There are also heat pumps that draw energy from the ground or water.

A heat pump uses electricity to run but produces more energy than it uses, making it an efficient way to heat your home and hot water. While the efficiency of an air source heat pump will gradually reduce as the outside air temperature falls, they can still extract natural heat from air when the mercury dips as low as -15 degrees C.

British electricity is increasingly powered by renewable energy such as wind, making heat pumps an eco-friendly heating solution. Unlike boilers, heat pumps don’t emit local air pollutants, such as nitrogen dioxide, making heat pumps greener and cleaner than fossil fuelled boilers.

Can they be fitted in any property type?

Because air source heat pumps typically sit in a box on the exterior wall of a building or on a patio, they are relatively easy to install. From high rise flats to semis, air source heat pumps can be retrofitted in most housing types, according to the Energy Savings Trust. 

Homeowners can usually install heat pumps under Permitted Development rights. But It’s always worth checking whether you need planning permission from your local planning authority, especially if you live in a conservation area or a listed building.

How much does a heat pump cost?

While prices vary, the cost of an air source heat pump is approximately £8,000 to £14,000. The final bill depends on the size of your home and how much preparation work needs to be done. In comparison, the average installation cost of a new boiler in the UK is between £500 and £1,500.

The high upfront cost can be off-putting for many people, but it is still a niche industry and it is expected prices will fall as the technology becomes more mainstream. Government has promised to make heat pumps more affordable by offering households £5,000 grants from April next year.

There is other cash help available now. The Renewable Heating Incentive (RHI) – excludes Northern Ireland - offers quarterly payments over seven years based on the heat you generate. This helps to recoup some of the initial cost of installing a renewable system compared to a traditional boiler. The scheme is due to end on March 31, 2022, as the new grant scheme kicks off.

How different are heat pumps to run?

The main difference is heat pumps deliver heat at a lower temperature than a boiler, so they need to be on for much longer periods of time.  There isn’t the immediate boost you can get when you feel cold and you fire up a gas or oil boiler.

But with a heat pump, the system works out the most efficient way to keep the house to the temperature you require. It’s possible to programme in changes, such as being away on holiday and your return time, so the house will be warm and toasty for your return.

Do you need a well-insulated home?

All heating systems work more efficiently in well-insulated and airtight homes. Improving home insulation to save energy is key to cutting carbon emissions from houses in the UK. That said, because heat pumps operate at a lower temperature than a boiler, they will only work effectively in homes that are insulated and draught proofed. Otherwise, the heat leaks out and can’t be boosted quickly enough by a heat pump. Gas boilers, in contrast, heat houses very quickly so they can replace the heat which seeps out of a house.

If you live in a leakier house, putting in loft insulation, cavity wall insulation and double glazing could help keep costs down in running a heat pump – just as they would if your home is heated by a gas boiler. Some period properties and listed buildings can’t be insulated to modern standards.

What other changes might be needed, such as replacing radiators with underfloor heating?

It is highly likely that all the radiators in your home will need to be replaced with higher output versions along with a heat pump compatible cylinder, according to David Hilton, an expert in sustainable building and energy efficiency and a director of Heat and Energy Limited. Larger radiators help to ensure heat pumps will warm the space sufficiently.

Pipework will also need to be inspected to make sure it is secure, the right size and type of pipe. This is especially true if you are upgrading a gravity fed system to a high-pressure system – the pipework must be insulated and plumbed in a parallel configuration, said Hilton.

Underfloor heating operates at a lower temperature than radiators and gives a better spread of heat. If you are doing a wider refurb, it may be better to replace radiators with underfloor heating, though that means taking up the floor to install it, so more expense and disruption. It is not essential to fit it, however.

Do you save money with a heat pump?

According to the Energy Savings Trust, a properly installed heat pump is more efficient than a gas boiler, which could save you money on your heating bills. You will still have fuel costs with a heat pump because they run on electricity, but you will save on the oil on the fossil fuel you no longer use.

Because electricity is currently a lot more expensive than gas or oil, the running costs often work out similar. While you no longer need to pay for gas or oil, your electricity bill is likely to increase. Look for tariffs which allow use of electricity for running heat pumps when it is off-peak and cheaper.

The Energy Savings Trust estimate that replacing an old G-rated gas boiler with an air source heat pump, for instance, could save the average four-person household £375 a year on heating bills.

There are higher environmental levies on electricity than gas at the moment to pay for subsidies for renewables, which were brought in to help clean up the electricity system. Campaigners are lobbying for levies to be added to gas bills instead.

Will I have to rip out my old boiler for one of these new technologies?

The Government has set an ambition for all new heating systems to be low carbon from 2035 but says no-one will be forced to remove existing fossil fuel boilers. Instead, households will be encouraged to install the eco-friendly option over the next 14 years as they replace their old boilers.

Some 22 million homes across the UK contribute more than a third towards the country’s carbon emissions, which must be slashed to ‘net zero’ by 2050 under the Government’s legal obligations. Heat pumps are a sustainable option as they use natural heat and don’t emit any greenhouse gases.

If you are considering extending or altering your home, you may find some of these services useful: