How do heat pumps work?
Although there are different kinds of heat pumps, they all work in the same way. Heat pumps transfer heat from the outside environment into a building through a four-step process:
- Evaporation
- Compression
- Condensation
- Expansion
This is known as a refrigeration cycle. This heat pump diagram illustrates the process:
1
Evaporation
Heat pumps take in heat from the air or ground or sometimes water, transferring it to a heat exchanger that contains a liquid refrigerant. This refrigerant absorbs heat from the outside and evaporates, turning it into a low-pressure, low-temperature gas.
2
Compression
The gas is transferred to an electrically powered compressor that compresses the refrigerant. This compression increases the pressure of the gas, which raises the gas temperature.
3
Condensation
The hot gas reaches the heat exchanger, where it’s circulated and transfers its heat to a cold water circuit. This causes the water to heat up as it absorbs heat from the gas. Once the water has reached the desired temperature, usually around 55 degrees, it’s sent to your home’s radiators and underfloor heating to warm your house.
By transferring heat to the water circuit, the refrigerant cools down enough to turn it back into a liquid.
4
Expansion
The cooled refrigerant moves through an expansion valve, which lowers the pressure and allows it to absorb more heat energy. From there it’s pumped back into the heat exchanger to repeat the cycle.
There are some differences in how heat pumps work, depending on what type of heat pump you have:
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In air source heat pumps the cold refrigerant starts its journey in the evaporator. It absorbs heat energy from outside air blown across a heat exchanger using fans.
Although the air is cool in the winter, there’s still plenty of energy available because of the large volume of air that passes over the heat exchanger.
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Ground source heat pumps gather heat energy from the ground by circulating a water-antifreeze mixture (known as ‘brine’) through underground pipes. This is pumped to a heat exchanger inside the house or an outbuilding.
Pipes are either laid horizontally over a large area, or sometimes go down deep boreholes in the ground. The brine passes through the heat exchanger, transferring the heat to the refrigerant, which continues its journey to the compressor.
Cut through the hot air on heat pumps
We debunk some common myths about heat pumps. Get the facts at our heat pump hub.
Visit our heat pump hub
What kind of heat pump is right for me?
Heat pumps are suitable for all kinds of homes. It’s a common heat pump myth that certain kinds of houses can’t have heat pumps installed.
The kind of heat pump that suits your home usually comes down to:
- your budget
- how much space you have
Use our online assessment tool, Go Renewable, to find out what renewable technologies, including heat pumps, are suitable for your home.
Air source heat pumpsare the most common type of domestic heat pump in the UK and are suitable for most types of home. They’re relatively small and cheaper to install than other types of heat pump. The heat pump is normally provided as a ‘monoblock’ that sits outside the home. The heat pump unit is around the size of two wheelie bins side by side.
Ground source heat pumps are better suited to those who have a large garden or outdoor space to run a loop of underground pipes or sink boreholes. They tend to be more efficient than air source heat pumps but are considerably more expensive to install.
For all heat pumps you need space to put a hot water cylinder, ideally inside the house. Having underfloor heating usually works well for heat pumps. You may need to upgrade any radiators to have a higher surface area, which are suitable for heat pumps.
For more information, read our guide to the differences between air source and ground source heat pumps.
If you live in a smaller property, like a flat or park home, you may be better suited to an air-to-air heat pump. These heat pumps heat your home using fans rather than radiators or underfloor heating.
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Depending on your circ*mstances, you may want to learn more about other kinds of heat pumps:
- Hybrid heat pumps let you use a heat pump alongside a fossil fuel boiler.
- Solar assisted heat pumps use solar panels to turn sunlight into heat energy to warm up the refrigerant, supporting the heat pump.
- Water source heat pumps absorb heat from nearby water sources such as lakes, lochs and rivers and are otherwise similar to ground source heat pumps.
- Exhaust air heat pumps extract heat from ventilation air as it leaves the building, capturing heat that would otherwise be lost.
- Cascaded heat pumps allow multiple heat pump units to work together for homes with high heat demands.
How efficient are heat pumps?
Heat pumps aremore efficient than other heating systems and generally produce around three times more energy than they take in – 300% efficient. They’re more efficient as the heat they provide is harvested from the environment rather than coming directly from an energy source, such as natural gas.
Compare this to an A-rated gas boiler, which has an efficiency of around 85%. This means that for every unit of gas used in the boiler, it produces 0.85 units of heat. And oil boilers are 88% efficient, so produce 0.88 units of heat for every unit of oil burnt.
In a heat pump the amount of heat produced for every unit of electricity usedis known as theCoefficient of Performance(CoP).So,if a heatpump has a CoP of 3.0,then it gives out threeunits of heat for every unit of electricity it uses.
Every heat pump has a published datasheet telling you what its measured CoP is. This published CoP is measured at a single point in time, under specific test conditions.
However, in real life, heat pumps experience external temperature variations throughout the year that affect their efficiency. So the CoP isn’t always helpful in understanding what your heat pump will cost to run over the year.
To help with this, the seasonal coefficient of performance or seasonal performance factor (SPF) shows the efficiency of the heat pump averaged across the whole year.
Heat pump installers must calculate the SPF based on their system design for your home. This calculation shows how the heat pump should perform given:
- the average temperatures at your location
- the size of your radiators
Your heat pump installer should share this calculation with you before they start any work. The SPF gives you a better indication of your expected system efficiency, running costs and possible running cost savings than the CoP figure.
How much do heat pumps cost to install?
The cost to install a heat pump largely depends on what kind of heat pump you’re looking at:
- Air source heat pumps tend to cost between £14,000 and £19,000 to install.
- Ground source heat pumps cost between £28,000 and £34,000 to install, depending on how you install the pipes.
The cost of a heat pump installation is also influenced by:
- The size of your property.
- Whether you live in a new build or an existing house.
- How much work is needed to adapt your existing heating system for a heat pump.
What financial help is available for a heat pump?
There are different funding options available to help to cover your installation costs, depending on where you live.
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The Boiler Upgrade Scheme is a grant of up to £7,500 to help fund a heat pump.
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Home Energy Scotland offers a loan of up to £7,500 for home renewable upgrades. You can also et a grant of up to £7,500 (£9,000 in rural areas) for energy efficient upgrades.
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There are no dedicated heat pump schemes in Northern Ireland. But there is help available for other energy saving measures such as insulation. Get in touch with NI Energy Advice to see what funding is available for you.
How much do heat pumps cost to run?
On average, heat pumps cost around £1,540 to run per year.
Your specific running costs will depend on a range of factors including:
- How much heat your property needs, and your preferred room temperature.
- Your electricity tariff.
- The type of heat pump you install.
- How efficient your heat pump’s settings are, and how it’s operated.
- The average air or ground temperature where the heat pump is.
What do I need to prepare for a heat pump?
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Heat pumps are suitable for all homes. So even if you don’t have lots of insulation, a heat pump could still work for you.
One of the factors your heat pump installer will use when calculating your home’s heat needs is the level of insulation and draught-proofing it has. Improving the insulation of your home makes your home more comfortable and reduces your heating costs by:
- Reducing heat loss through your walls, floor and ceiling.
- Keeping your home warm for longer so the heat pump needs to work less.
In some homes, upgrading your insulation may not be practical or cost-effective. Insulation installers can visit your home and advise where rooms could be improved with appropriate insulation.
Many houses may benefit from improved insulation and draught-proofing, but you should speak to an insulation specialist if you live in a house that:
- Was built before 1919 and likely has solid walls.
- Is a listed building.
- Is in a conservation area.
Your installer should be able to design a system that works for your needs. So if you can’t install insulation, or increase your radiator size, you can use a heat pump that delivers water at a higher temperature.
You could also consider ahybrid heat pump system, where your heating is topped up with traditional heating like gas or oil.
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Ideally, a heat pump should send hot water to your radiators at between 35 and 45 degrees to be most cost effective. Compare this to fossil fuel boilers, which are designed to send water to your radiators at up to 75 degrees.
You can still heat your home effectively even at these lower temperatures. To do so, you need to increase the size of your radiators to maximise the surface area for emitting heat coming from the heat pump.
A ‘bigger’ radiator doesn’t have to take up more wall space. It just needs to have more surface area, which lets more heat into the room without needing to increase the water temperature. The large surface area of good underfloor heating means it should already be well suited to a heat pump.
You can upgrade your radiators from a single panel to double (K2) or triple (K3) panels to increase their surface area without taking up extra wall space.
If you can’t upgrade your radiators, you can get the same effect by running your radiators at a lower temperature for longer.
Some central heating systems from the 1970s have a type of pipe called ‘microbore’. It has a small pipe diameter, which means the heat pump can’t transfer water quickly enough to the radiators. If you think you have microbore pipe, speak to your installer when they survey your house, as it’s not suitable for a heat pump and will need to be replaced.
Will installing a heat pump help save money on my heating bills?
This largely depends on what heating system you’re replacing.
Generally, the high efficiency of heat pumps means that it should be cheaper to run than most other fuel types.
If you have a gas boiler (or often an oil boiler in Northern Ireland), heat pumps are likely to be slightly more expensive to run.
But, as energy prices fluctuate over time, we expect that heat pumps will become the cheapest as well as the lowest carbon form of heating available.
Here are the typical savings you can expect to see from the two most common types of heat pump:
Air source heat pump savings
Ground source heat pump savings
Do I need planning permission to install a heat pump?
In general, no – you shouldn’t need planning permission to install a heat pump. This is because most heat pump installations are considered to be a ‘permitted development’ provided you meet certain conditions such as the heat pump not being within one metre of a neighbour’s boundary.
But there are exceptions. For example, if you live in a listed building or a conservation area. It’s best to check with your local planning department before committing to installing a heat pump.
Find out more aboutpermission for installing renewables.
You should also tell your local district network operator (DNO) that you’re planning to install a heat pump. The DNO is the company responsible for bringing electricity from the network to your home.
Your heat pump installer will have all the information you need to complete the relevant forms and will often do this for you.
To find out more about registering a heat pump in England, Scotland and Wales, check out the UK Government website.
Getting the most out of your heat pump system
Your heat pump’s compressor works harder when there’s a larger temperature difference between the outside and the water needed in your home to provide your desired room temperature. The less the compressor needs to work, the less electricity the heat pump uses.
While you can’t control the outdoor temperature, you can design your heating system to maximise the heat you get from the heat pump. And with the right home upgrades, you’ll be able to heat your home comfortably without needing to increase the water temperature in the heating system. Making sure you don’t heat your home to too high a temperature will allow the system to work more efficiently.
Here are some ways you can get the most out of your heat pump:
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An air source or ground source heat pump needs to store hot water for when you need it. The size of hot water cylinder depends on the volume of hot water that you need. But you can often fit it inside a cupboard measuring 80x80cm.
While most heat pumps can provide water at 55 degrees, hot water in the cylinder needs to periodically reach 60 degrees or higher to kill harmful bacteria. Some heat pumps can deliver water to this temperature. But most systems are designed to use an immersion heater (an electric heater within your hot water cylinder) to top up the temperature, typically once a week.
An air-to-air heat pump doesn’t generate hot water. If you’re thinking of installing this kind of heat pump, consider an alternative way of heating your water, such as using an immersion heater.
If you don’t havespace for a hot watercylinder, you still have options.Somehybrid heat pumpsare designed so that the heat pump provides heating, while a traditional boiler provides on-demand hot water instead.
You could also consider:
- Installing aheat battery, which takes up less space than a hot water cylinder.
- Instantaneous hot water heaters, which you can install under your sinks to provide a smaller volume of hot water.
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As part of your installation your installer should set your heat pump’s controls to be as efficient as possible.
But you may find that after running the system for a while in a range of outside temperatures, you need to adjust it.
Heat pumps come with several settings that might be confusing at first. We take you through these in our guide to making your heat pump more efficient.
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Most heat pumps are easy to maintain. They’re about as much work to maintain as a gas boiler.
Heat pump warranties can last for up to 10 years throughQuality Assured National Warranties. Many manufacturers also offer options for warranty extensions for a fee.
With regular scheduled maintenance, you can expect a good quality heat pump to work for 20 years or more.
You can get your heat pump serviced for around £150. Typical checks include a visual inspection of the:
- water pump
- external pipes
- fittings
- electronics
You should get your heat pump serviced once a year. Some warranties say you need to service your heat pump regularly to keep your warranty valid.
Ground source heat pumps may also occasionally need the ground water loop to be re-pressurised or have the quality of the antifreeze checked. You should get a professional to do this every two to three years or as required.
How long does it take to get a heat pump?
Due to the increasing demand for heat pumps, the wait time for a heat pump can be several months. So if you’re thinking about getting a heat pump, it’s best to start the process sooner rather than later.
The installation itself typically takes between three and five days, depending on how complex the installation is. The installer might need more time if:
- You need larger radiators in your house.
- You’re installing a ground source heat pump and they need to drill or dig to lay the pipes.
What else do I need to think about before I get a heat pump?
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Research from acoustic experts and interviews with residents with heat pumps reveal that they’reabout as loud as a fridge or a gas boiler. In fact, those with heat pumps installed said they were more likely to notice the sound of traffic outside their home than their heat pump.
Heat pump noise is typically in the range of 40 to 60 decibels. You may find they are a little louder in colder temperatures as they work harder. But you can still have a normal conversation right next to them. Additionally, some manufacturers offer ultra quiet models.
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Installing a heat pump may cause some disruption to your daily routine, depending on how much work needs to be done.
Typical work in a heat pump installation includes:
- Building a plinth outside for an air source heat pump to stand on.
- Adding pipes through the wall to where your existing boiler is.
- Installing or replacing a hot water cylinder.
- Upgrading radiators where needed.
- Installing underfloor heating where needed. This involves taking up floor coverings and floorboards.
- Digging trenches or boreholes to install the heat pipe (for ground source heat pumps).
If you think this will disrupt your day-to-day routine too much, consider making arrangements to be away from home during the installation. However it’s often possible to stay in your home while work takes place.
