Heat pump FAQs

Want to decarbonise your home heating by installing a heat pump, but not sure where to start or if your home is even suitable? We’ve got you covered.

Earlier this year, we brought together heat pump installer Leah Robson, policy expert Richard Lowes, heat pump owner Margaret Biddle, and campaigner Neil Jones, to get answers to some of the most common questions people have when they’re considering getting a heat pump.

A recording of the live Q&A event is available to watch on YouTube, but we’ve also written up a summary of the most common questions here so that you can easily find what you’re looking for.

+ What is a heat pump?

A heat pump is a clean replacement for a gas boiler, powered by electricity rather than directly burning fossil fuels. Heat pumps are super efficient, and ready to heat our homes without heating the planet. The potential of this amazing technology is already being recognised in Western Europe, with both France and Sweden already installing 1 million heat pumps in homes.

+ How do they work?

Heat pumps don’t generate heat - instead they extract ambient heat naturally stored in the air or the ground to heat our homes. Air-source heat pumps are the most common type, drawing ambient heat from the air using a fan - while ground-source heat pumps use pipes buried underground to pull heat from the earth. Importantly, both work during the winter months.

Air drawn by the fan passes through a system of coils with a special liquid (called a refrigerant) that absorbs heat from the air, but at a low temperature. The refrigerant is then pressurised - which increases its temperature. Finally, this higher temperature heat is transferred across to the water that circulates around radiators inside a building, in order to warm it. This whole process is powered by electricity, which can be produced from low or zero carbon sources. The process is slightly different for ground source heat pumps, but the essential elements are the same.

+ Will it keep me warm enough?

Different models of heat pump reach different temperatures, with this new Vaillant model reaching up to 65 degrees. But what keeps one person warm will differ from person to person, but here’s what Margaret and Richard said when this question came up in our Q&A event.

Margaret explained that her 8kw air-source heat pump keeps her three-bedroom bungalow ‘really warm and cosy’. She described her heating as “nice and steady, not oppressive”, and her hot water as plentiful. She has underfloor heating and explained that good insulation and effective ventilation was key to making sure her home is comfortable. Richard confirmed that his traditional low temperature heat pump system is also effective at keeping his home warm. He pointed out, however, that this largely depends on your expectations (for example, many people want to do their laundry at 60 degrees, but that’s actually unnecessarily hot). Richard’s heat pump produces temperatures in radiators up to 45 degrees (possibly 40-55), which is hot enough to just about hold without scolding. It is hot, but not as hot as 60-70 degree radiators you might get with a gas boiler. Similarly, when running hot water for his bath or shower, the temperature reaches 46 degrees - which many people feel sounds low, but is still too hot to get into.

+ Is my home suitable?

Overall, every home is suitable for a heat pump, and every home can be made warm with a heat pump system. Margaret has 3 bedroom bungalow and Richard has victorian mid-terrace with stone walls. Both enjoy comfortable heat, low bills, and really good carbon-savings.

You need to treat houses as unique - heat pump installation is not the same as a gas boiler, it’s a bit more complicated. Fortunately, there are different kinds of heat pumps and different ways of installing them, and what you go for will depend on the specificities of your home. For example, air-source heat pumps need to sit on flat surface (eg the ground or a flat roof) which might not be suitable for all flats, and older buildings that are harder to insulate might be best served by underfloor heating or larger radiators. In both cases, you could also consider choosing an air-to-air heat pump which are similar to air conditioning units.

If you’re in a flat, it will probably be best to team up with others in your building. It could be that you use one large central heat pump, or small individual heat pumps in each flat (eg. Kensal’s shoebox heat pump) that could be connected to a shared ground-loop outside. Either way, if the whole block is retrofitted at the same time, you can ensure maximum energy efficiency.

Find out the best option for your home by booking an assessment with a certified installer.

+ How much does it all cost?

Installation costs: According to the Energy Saving Trust, the typical cost of a heat pump installation can be as low as £7k and there are schemes available to substantially reduce that cost (see below). Costs vary quite a bit depending on the extent of work required for your home. Leah explained that an average air-source heat pump installation for her company (which includes a new hot water cylinder, the heat pump unit and replacing some radiators) in South-East England would cost closer to £14k. A ground source heat pump system would cost a fair amount more (around £45k).

A lot of the costing is due to staff time rather than the actual heat pumps and pipes, and so it will vary from place to place and depend on which company you go with. It’s always worth making sure your installer is MCS certified.

Running costs: Historically, air source heat pumps costed about 10% more than gas boilers to run. However, with the recent rise in gas prices, they are now roughly equivalent. That being said, there are some things you can do to bring the costs down by as much as £600 per year.

If you have solar panels, you’ll likely see significant savings in your electricity bills - and even more so if you use them to power your heat pump. An integrated solar and heat pump system should save you an estimated £300--£400 each year.
Switching to a ‘smart tariff’ for electricity can also help. Richard uses Octopus' Go tariff, which has brought his unit rate down by a third.

+ What kind of financial support is available?

There are a few routes for financial support available to people across the UK, and which one(s) you have access to will depend on where you live, your income, and whether or not you live in social housing.

The government’s current scheme for supporting households in England and Wales to get heat pumps is called the Boiler Upgrade Scheme. This is given as a £5000 voucher to contribute to the initial cost of installation (or £6000 if you’re installing a ground-source heat pump). Your installer will apply for the voucher on your behalf and once accepted, you have three months to have the heat pump installed. However, this funding is limited. The government has committed to give this voucher to 30,000 households per year for the next three years.

If you live in social housing, it’s worth checking that your landlord or housing association is aware of the social housing decarbonisation fund which can be used to carry out energy efficiency upgrades in tenants’ homes.

Those on lower incomes, may also be able to get help with the costs of installing a heat pump from their council via the Home Upgrade Grant that came out last year.

If you’re in Scotland, you might be able to get a very low interest loan to help with the upfront costs of heat pump installation, and possibly additional support via the Warmer Homes Scotland scheme. For more information see Home Energy Scotland.

Finally, many households in Wales are eligible for funding for energy efficiency improvements and heat pumps via [the Nest scheme].18

+ How ‘green’ are they?

Heating buildings with fossil fuels is a massive contributor to UK carbon emissions, accounting for between 20 and 25% of all emissions each year. Currently, 17 million UK homes are still reliant on fossil fuel guzzling gas boilers, which emit twice as many carbon emissions as every gas fired power station in the UK combined. The gas we burn to heat our homes is fuelling the climate crisis, causing fires, floods and extreme weather all around us.

Heat pumps will help us get ahead on climate change, and off fossil fuels. First off, heat pumps are extremely efficient. For every unit of electricity you give to a heat pump, it produces 2-4 units of heat energy! This makes heat pumps up to four times more efficient than outdated and dirty gas boilers. What’s more, heat pumps have the potential to be run solely on renewable electricity, which means they offer the possibility of zero carbon heating. And with the government’s commitment to a carbon-free UK electricity grid by 2035, this isn’t a pie-in-the-sky dream, but a reality that can and must be achieved.

+ What kind of CO2 savings should I expect?

According to the Energy Savings Trust, if you’re switching from a gas boiler, you’re likely to see a 40-45% reduction in carbon emissions. And if you’re switching from oil, you're looking at 56-59% reduction. What’s more, with each year renewable electricity accounts for a greater proportion of the UK’s electricity grid, meaning that the carbon savings of switching from gas or oil to heat pumps will become even greater.

It’s also worth noting that you’ll also see benefits to local air pollution (Gas boilers emit nitrous oxide and heat pumps don’t).

+ Should I focus on getting my own heat pump, or pushing for a district heating system?

District heating (also known as ‘heat networks’) is very popular in Scandinavian countries and Eastern Europe. Rather than having a gas infrastructure or electricity infrastructure to provide heat to homes, you’d have a network of hot water pipes (or steam pipes). You can’t put district heating systems everywhere, but they are particularly impactful in dense urban areas or dense buildings (like blocks of flats) - as you can get much better overall efficiency in terms of cost (rather than having 200 individual boilers, you might have two big boilers and a series of pipes). Overtime it can be very green, because you can use any kind of electricity such as solar or biomass to run the system.

Most urban areas in the UK should be already developing heat networks or have a plan for one. However, lots of local authorities are stretched and behind on their plans. You could lobby decision makers to move forward with district heating in your neighbourhood, but it could take some time. Whereas, if you got your own heat pump, you could enjoy immediate savings

To set up district heating for shared occupancy buildings, you’d need to get leaseholders on board, shared access rights, permissions etc.

+ How do air source, water source, and ground source heat pumps compare?

* Air-source heat pumps draw latent heat from the air. As they are fixed above ground, they are usually the most suitable for more properties, and are the most commonly used heat pumps for domestic systems. Although air-source heat pumps are very energy efficient, they are slightly less so than ground and water-source systems. This is because the air temperature changes much more significantly than ground temperatures, and so they need to work much harder in the winter to provide the same heat.

Ground-source heat pumps can get heat from the ground or from water. Typically they will have boreholes or pipework laid horizontally about a metre under the surface of the ground. They are fractionally more efficient than air-source systems, and have constant performance across the year. However, these systems are quite expensive (£15-20k for boreholes alone) and you need quite a lot of ground (roughly the size of a football field).
Water-source heat pumps draw latent heat from a water source. They are suitable for fewer properties than air-source heat pumps. You’d not only need to be very close to a water source (for example having a stream running along the bottom of your garden which doesn’t run dry in the summer), or have shallow aquifers underneath your home, but you’d also need space for a ground-source heat pump as well.
+ What about high temperature air-source heat pumps?

See The Heating Hub for an excellent explanation of high temperature ASHPs and a list of available models.

+ Aren’t they noisy?

Noise is a common concern amongst people who are considering getting a heat pump (and their neighbours) - but from those we’ve spoken to, it’s nothing to worry about.

Heat pumps do have a sound, but it’s no louder than a running fridge or a gas boiler. One thing to bear in mind is that the noise is quite different to that of a fridge or gas boiler (Margaret described the noise as more of a little hum than a rumble). What’s more, there are planning regulations that ensure that heat pumps don’t disturb your neighbours. For example in Wales, there’s a rule that your heat pump must be at least three metres from the neighbours’ boundary (in England the requirement is a one metre distance).

+ Is my home energy efficient enough?

If you’re planning on making use of the government’s Boiler Upgrade Scheme (which will replace the Renewable Heating Incentive from April 2022), you will need to take a look at your home’s Energy Performance Certificate (EPC). If your EPC does not show any recommendations for additional loft or cavity wall insulation, then you should be good to go. However if you do need additional insulation, or if that is missing from the EPC, then you will be able to sort your insulation at the same time as your heat pump is installed.

Either way, when you’re getting a heat pump it’s a good opportunity to get an installer round to do a heat loss survey. This would tell you what size system you need or what additional insulations measures to take and what the balance of that would be. But even if you’re not ready to get a heat pump, maximum insulation is always going to be beneficial. Insulation is always important, no matter what your heating system is as it stops heat escaping, meaning you need less energy to keep your home warm (resulting in less carbon emissions and cheaper heating bills). So we’d argue to make that a priority.

Since the Green Homes Grant was removed last year, there’s been very little government support for energy efficiency improvement. This is a huge hole in the government’s recent Heat and Buildings Strategy 2021 (and one of the things we’re asking decision makers to address). If you haven’t yet written to your MP, asking them to urge decision makers to better support people to decarbonise their home heating, we have a web tool you can use - all you need is your postcode and two minutes.

+ Will I need new radiators, pipes, and/or a new water tank?

As with insulation, there is no general answer to this question, rather it needs to be worked out on a house-by-house basis. All MCS-certified installers will do a heat loss calculation for your home. This will involve measuring every room and window in your home to work out the heat loss of each room and to work out whether your existing radiators are sufficient to run at a lower temperature.

Because heat pumps reach lower temperatures than gas boilers, it is often assumed that you’ll need larger radiators to heat your rooms.If this is the case, it might be a matter of simply swapping the radiator from a single panel radiator to a double panel one. All of this is something the installer should tell you after they’ve carried out the survey. However, Leah has found that a lot of people have radiators that will work fine as previous installers have chosen oversized radiators for the gas boilers (it’s simpler to over estimate).This is good news, because it means many homes are already set up for heat pumps.

In terms of pipes, ideally you’d be connecting the heat pump to radiators with 15mm copper pipes, with slightly larger pipework in the floor/ceiling. Since the 1990s, a lot of houses in the UK have been built with smaller 10mm plastic pipework (known as microbore). Leah advised us that people should be wary of installers who take one look at your microbore piping and insist that it’ll all need to be removed - it might not be the case. Microbore can still work if you have a good installer, but it all needs to be properly calculated, so make sure your installer has a proper look.

Finally, water tanks - if you have a combi-boiler (the type that produces hot water as soon as you turn your tap on), you’ll need to get a water cylinder with your heat pump. There are options if you struggle to fit one in your house (Leah suggested looking at the Sunamp heat batteries as more compact cylinders).

+ How disruptive is it to get a new heat pump installed?

This, again, will entirely depend on the extent of work you’re having done. If you have great insulation and that your pipework and radiators are all suitable, the installer will just need to come along and connect up your new heat pump - which is a fairly simple job.

Leah explained that a typical installation would involve installing or replacing a water cylinder, fitting the heat pump, and replacing a number of radiators. This would take roughly seven to eight working days (so expect there to be two weeks where someone will be working in your house). During the process, it’s likely you’d be without heating for a day or two and without hot water for a day. That being said, many people install heat pumps as part of a much bigger project to improve their home energy systems. Margaret, for example, moved out of her home for a full year to do a major retrofit; the floors and kitchen were removed to fit new pipework and solar panels. So for Margaret this was a much more disruptive job, and much more expensive too (the £5000 grant was just a fraction of what was needed), but now it’s done and working efficiently, she says it feels worth it.

+ How much space do they take up (and where can I put one)?

If you’re looking to have an air source heat pump, you’d need something outside (roughly 1m x 1m x 0.4m), so you need a space to put that that is also in line with local planning rules (eg. in England, the heat pump needs to be 1m distance from your neighbour’s boundary).

If you want your heat pump to produce the hot water, you need somewhere to store that hot water, so one of the main things to consider is whether you have space for a hot water cylinder inside your house. For those who have hot water tanks already, your airing cupboard would usually be suitable for a hot water cylinder. You also might need a buffer tank (roughly 1 x 0.5m) - for more information on buffer tanks see the explainer blogpost by the team at Thermal Earth.

Finally, if you’re looking at getting an air-to-air heat pump (which are more like air conditioning units), you can put that on the side of the house, and attach it to the wall. These systems avoid the need for radiators but you will need a cassette on the side of the building to blow air out.

+ Shouldn’t I wait until green gas is available so that I can continue to use my existing boiler?

A lot of people have been asking us recently about ‘green gas’. While this is certainly an exciting project, it wouldn’t be well suited to decarbonising home heating on a mass scale. Grass is used to produce the gas, but it'd be impossible for the UK to produce enough grass to meet UK demand (there’s simply not enough space!). What's more, this system would require a lot of transportation, which would add to the carbon footprint. Heat pumps, on the other hand, are much more efficient than biogas boilers, and are available now for homes across the UK.

+ Technology is always improving. Should we wait for new better heat pumps to reach the market?

Heat pump technology is always improving. Some heat pumps just entering the market now can reach higher temperatures, meaning more houses could potentially use these heat pumps without need to upgrade their insulation or radiators. That being said, the heat pumps currently on the market are more than capable of heating the majority of homes across the UK, and we need to cut emissions fast. Can we really afford to delay?

+ How long should a new heat pump last?

On average, a heat pump will last around 10 to 15 years. Manufacturers will often give a seven-year warranty, and MCS installers should also give a two year warranty on workmanship. . It’s worth noting that a condition of the government’s RHI (the £5000 grant towards your heat pump) is that you have it serviced every year.

+ How can I find a trustworthy installer?

A great place to start is mcscertified.com/find-an-installer/. Simply fill in where you are and what you’d like fitted in your home, and the site will generate a list of approved installers in your region including their contact information. We’d also always suggest getting recommendations - look through reviews and speak to people who have had good or bad experiences. [https://mcscertified.com/find-an-installer/]

+ There’s a water source on/near my home. Could it power a heat pump?

Yes, if you are very close to a reliable water source (such as a stream at the bottom of your garden that doesn’t run dry in the summer), then you might be able to install a water-source heat pump. You’d need to have an installer come and carry out a survey to check.

+ Do heat pumps have cooling functions?

Some air-source heat pumps have both heating and cooling functions; they can pump either hot or cold water through your radiators to provide comfortable temperatures in summer and winter. However, these models can cause condensation, so our panel advised that it’s better to have a separate system with different pipes and a separate unit for cooling (which is like a radiator inside a fan).

Another option is to use air-to-air heat pumps, which have been very popular in Sweden where the cooling mechanisms are effective in their hot summers. However, the UK public are less familiar with air conditioning units, so it may take a bit of getting used to. What’s more, air-to-air heat pumps do not provide hot water, so you’ll need a separate hot water system if you were to go down that route.

+ Would a heat pump integrate with my solar power system?

Yes, it’s a great idea to connect your heat pump and solar power systems, particularly if you have a storage battery - you’ll likely see savings in both carbon and bills!

+ Are there any planning issues with listed buildings?

You will usually need planning permission for a heat pump in a listed building - speak to your local planning authority for advice.

+ Should I wait until my boiler shows signs of breaking down before considering a change?

Planning and booking in heat pump installation can take some time, so we’d suggest you don’t wait until your boiler breaks - otherwise you might be stuck without any heating or hot water.

+ How can we go about getting a heat pump for our local school, office, or community centre?

This is something we looked at as part of our Powering Parks project with Hackney council - check out the toolkit poweringparks.wearepossible.org and share it with your local council.