Heat Pump FAQs

Heat Pump FAQs

Our Sustainable Homes Advice Service team have put together answers to some frequently asked questions to help you if you’re considering making the transition to low carbon energy or already have a heat pump.

What types of heat pump are there?

An Air Source heat pump will take heat from the air outside your house and use this to warm water in a central heating system to heat radiators. It will also produce hot water for your hot water cylinder.

An Air-to-Air heat pump takes heat from the air outside your house in the same way, but instead of using radiators, fan units called cassettes are used to blow warmed air around your house. Some air-to-air heating systems can also provide cooling (working in reverse as an air conditioner) and can dehumidify your house as well. An air-to-air heat pump does not provide hot water, so an immersion heater in a hot water cylinder is also needed.

A Ground Source heat pump takes heat from the ground, either using a vertical borehole or trenches with a long pipe that has a liquid in it that draws heat from the surrounding ground. The heat pump then puts this heat into radiators in a central heating system and hot water in a hot water cylinder.

If you are fortunate to live close to a river or even the sea, a Water Source heat pump can be used in the same way to draw heat from water. Due to the technical challenges of this set-up, water-sourced heat pumps are not common, but the technology for using the heat is the same.

Does a heat pump work when it’s freezing outside?

Heat pumps can work in temperatures as low as -15°C. In fact, Finland has the highest rate of heat pump installs in Europe, despite being one of the coldest countries.

Air source heat pumps must work harder when the air is colder but will be able to manage a frosty morning; the winter climate in Cornwall is quite suitable for a heat pump. The outdoor temperature does not affect ground source heat pumps because the ground temperature 1-2 metres down remains constant all year round.

Can I use solar panels and a battery to power a heat pump?

Heat pumps can make use of solar electricity generated on-site, but most households using the power from a solar PV system will not make a big difference to heating bills. This is because a typical solar installation generates less energy than most houses will need to heat them over the course of a full year; additionally, most of this electricity is generated in the warmer months of the year when no heating is needed. Adding a battery to a solar system will not make much difference to this situation.

Solar panels can be more effective at heating hot water by using a solar diverter or programming the heat pump to heat the water more in the daytime. Solar diverters switch excess solar generation into the immersion heater in the hot water cylinder and can often supply up to 50% of the annual hot water requirements.

Do I need to insulate my house for a heat pump to work properly?

If you live in an uninsulated house, then you might find that a heat pump struggles to keep your house warm, or it is very expensive to run. Heat pumps work best in insulated houses because the pumps distribute heat at a lower temperature compared to a fossil fuel or electric heating system, and so good insulation levels will reduce heat losses.

Do I need underfloor heating?

Heat pumps work perfectly well with radiators, so underfloor heating is not required. However, heat pumps are more efficient with underfloor heating because the system will work at a lower temperature, about 35°C, to avoid burning people’s feet. Underfloor heating is more expensive to install than radiators, and the property needs to be very well insulated or the lower heating temperatures will not be able to provide adequate heating into your main living spaces.

I already have central heating – do I need to replace all my radiators?

An installer should check if your existing radiators and pipework are suitable for a heat pump. They will outline which radiators need upgrading, usually replacing them with larger radiators, and if the pipework will need to be changed. Microbore central heating systems do not work with heat pumps and so a full system upgrade is required.

Are heat pumps expensive to run?

Currently, heat pumps typically cost a bit more to run than fossil fuel heating systems, especially mains gas; they typically cost less than half as much as electric heating (night storage or panel heaters).

Why is my heat pump costing so much to run?

Some people contact us because they think their heat pump is costing them too much to run, or because they don’t think it’s heating their home properly.

There could be many explanations for high electricity costs that are not related to the heat pump.

You are welcome to call us to review what is happening; we can check how your heat pump is set up and look at your other energy consumption to help identify what the issue is and what steps will help bring your costs down.

How much does a heat pump cost to install?

Installation costs vary because the set-up and requirements of every house is different. However, government figures from the Boiler Upgrade Scheme grant show that air source heat pumps typically cost between £11,000 and £15,000 to install (before any grants are applied).

Ground source heat pumps typically cost between £18,500 and £36,000 to install (before any grants are applied) – the higher cost is due to the ground works for the pipework that supplies heat to the heat exchanger unit.

Air-to-air heat pumps are typically about half the cost of air source heat pumps that supply a central heating system, to install. Their running costs can be the lowest of all the heat pump types and they can be more effective at heating less well-insulated buildings. The fluids that move the heat to the cassettes which heat and blow warm air around, are regulated under the F-Gas rules, so you need to speak with an F-Gas accredited installer about quotations. Because they are classed as a type of air-conditioning, as the technology is commonly used, there is currently no government funding available for them.

What carbon emissions do heat pumps produce?

Heat pumps are the best form of heating to use in terms of reducing carbon dioxide emissions; they produce several units of heat for every unit of electricity used to power them. Aside from the emissions generated in manufacturing new systems, the carbon emissions from operating a heat pump will continue to drop as we see an increase in the proportion of renewable energy which is used to supply the UK’s electricity network, and the amount of fossil fuelled generation used is reduced.

Are heat pumps noisy?

Air source heat pumps use a fan to blow air through the outside unit which causes some noise. A noise assessment will be included as part of the pre-installation survey, to ensure that operating noise levels are not breached in nearby bedrooms and living areas in your and your neighbours’ properties.

Ground source heat pumps do not use a fan and are usually placed in a utility room away from living areas and do not produce any more noise than a fossil fuel boiler.

How much space does an air source heat pump need?


The outdoor unit generally requires a clear area with a solid foundation approximately 1m by 1.5m, with up to 1.5m clearance around the unit. There needs to be several metres of unobstructed space around the heat pump to allow enough air flow, to ensure that cold air does not get recirculated through the heat pump. Small yard areas at the back of buildings are not recommended for these heat pumps; however, as with air conditioning units, an air source heat pump does not have to be situated on the ground but can be raised and affixed to a wall above head height if this provides better air flow.

An installer will carry out a survey to check there is enough room to install a heat pump.


Heat pumps require a hot water cylinder, a smaller expansion cylinder and the associated pipework, so you will need space in your house to install these. The hot water cylinder is typically larger than a fossil fuel heated cylinder and the expansion vessel will need space, but they are designed to be retrofitted in place of existing cylinders (usually in an airing cupboard). In some cases, space for an additional buffer cylinder will be required, but these are only needed in specific circumstances. If you are replacing a gas combination boiler that has provided an instantaneous hot water supply, you will need to think about the best place to locate a hot water cylinder and expansion vessel.

How much space does a ground source heat pump need?


A bore hole requires only a few square metres for access for the drilling rig; once the hole is drilled, the trenching for the pipework to connect to the heat pump will be covered over and so, apart from a small cover to access the bore hole, no outside ground space is lost. For a heat pump using ‘slinkies’, horizontal coiled pipework, the trenches typically require 10m of trenches per kW of heat output and straight pipes require about 60m of trench per kW of heat output. Heat pump outputs typically range between 5kW and 17kW depending on property size and insulation levels. You will need access to a field or larger garden; a typical garden will not be big enough for the trenches.


The heat pump unit is located indoors and can be as small as a fossil fuel boiler to the size of a large fridge, but also a hot water cylinder, expansion vessel and possibly a buffer cylinder are needed, as well as the associated pipework. The hot water cylinder is typically larger than a fossil fuel heated cylinder and the expansion tank will need space, but they are designed to be retrofitted in place of existing cylinders (usually in an airing cupboard or utility room).

Will I need planning permission?

Only air source heat pumps installed under the Microgeneration Certification Scheme (MCS) standards and that provide heat only, fall under permitted development rights. If you live in a listed building, then you will need to apply for planning permission for an air source heat pump.

If your property is in a conservation area or World Heritage Site, then permitted development rules are more restrictive, so if you aren’t sure if you need planning permission, it is advisable to contact the Planning Department to clarify what is required.

Ground source heat pumps may not require planning permission because all the components are typically indoors, but we would advise contacting Planning at Cornwall Council to get a definitive answer on the necessary permissions, especially if you live in a listed building or conservation area.

Permitted development rules

If you aren’t sure if you need planning permission, then you can contact Cornwall Council for guidance.

How do I find a suitable installer?

The Microgeneration Certification Scheme (MCS) provides the industry standard for heat pump installations.

We recommend using an MCS accredited installer. Visit: Find a Contractor or Trustmark

Non-MCS accredited installers will provide high quality installations, but they would have to be considered on their own merits.

How long does a heat pump last?

Heat pumps should last around 15 years before they need replacing, dependent on how well-designed the system is. The rest of the central heating system should last much longer.

For an air source heat pump, if you live in a location that is exposed to coastal weather, the salts in the air blown by wind from the sea can be an issue. It is usually recommended that the heat exchanger unit is treated to minimise the corrosive action of salty, moist air when the heat pump is installed, and this may require recoating at periodic intervals – a local installer will be able to advise on this.

The underground pipework for a ground source heat pump is typically designed to last 100 years.

Is there any funding available to help me?

The Boiler Upgrade Scheme (BUS) currently offers a £7,500 discount on the install cost of an air source heat pump and £7,500 off the install costs of a ground source heat pump. The BUS is only available via Microgeneration Certification Scheme (MCS) accredited installers and it is the installer who applies for the grant, and deducts the grant from your invoice, meaning you pay less upfront.

To be eligible for BUS support, you must be replacing an existing fossil fuel heating system (such as oil, gas or electric) and your property must have a valid Energy Performance Certificate (EPC) with no outstanding recommendations for loft or cavity wall insulation. There is no grant support available for air-to-air heat pumps.

Getting the most out of your heat pump: How do I set up my heat pump to run efficiently?

Heat pumps work most efficiently when they maintain a constant temperature in the house. This is different to fossil fuel and electric heating systems which are generally switched on and off as required. If the whole house is cold because the system has been turned off, a heat pump can take several hours to get every room up to a comfortable temperature, which costs more than if the house was already warm. So heat pumps can be expensive to run, if not set up efficiently.

It is most effective to set the temperature that you want to achieve when the house is occupied and at other times, instead of turning the system off, set a ‘set-back’ temperature which is a few degrees lower. For example, if everyone in the house is out at work or school during the daytime, set the system for 21°C for first thing in the morning and for the evening and then ‘set-back’ to 16°C to 18°C for other times of the day and overnight.

Hot water should be set to a temperature comfortable for handwashing, usually about 45°C to 50°C. Once a week, a disinfection cycle will also be needed to heat the system up to 60 °C to kill any legionella bacteria growing in the water.

Getting the most out of your heat pump: other things you can do

  • Turn down the thermostatic radiator valves (TRVs) on the radiators in rooms that you do not use. If mould patches start to appear, the temperature is too low, so turn them back up to a level that provides enough warmth, and mould growth problems should be resolved.
  • For an air source system, make sure that the external fan unit is kept clear of debris. Check the vents of the unit are free of leaves in the autumn, and that things are not stored around the unit that could restrict airflow.
  • Make sure it is serviced regularly (annually) to ensure efficient operation.
  • Make sure you are on a single rate tariff. If you have switched from using storage heaters to an air source heat pump, then you may still be on a dual-rate tariff (e.g. Economy 7) which will cost you more money in the daytime, when your heat pump will be using electricity.