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As the world focuses on lowering carbon emissions to tackle climate change, heat pump systems have become a hot topic. So, you may be asking, what is a heat pump and how does it work?

In this comprehensive guide, we cover everything you need to know about heat pump systems: how they work, the different types available, heat pump installation cost, the advantages, and disadvantages to having one, and what you need to consider if you’re thinking about installing one.

View our range of heat pumps here

What is a Heat Pump?

Air Source Heat Pump

A heat pump is a system that extracts heat energy from outside, then brings it inside to heat a home or other property. The pump itself is located outside and looks similar to an air-conditioning unit.

Heat pump systems are better for the environment because they are run entirely by electricity rather than carbon-emitting fossil fuels. And because they deliver more heat energy than the electrical energy they use, they are typically more efficient to run than gas or oil-based heating systems or electric heaters.

How Does a Heat Pump Work?

An air source heat pump works a bit like a fridge operating in reverse:

  1. Inside the pump is a network of tubes filled with refrigerant that absorbs heat from the air
  2. Inside the pump is a network of tubes filled with refrigerant that absorbs heat from the air
  3. Using electricity, the heat pump then compresses the refrigerant to increase its pressure, raising its temperature and changing it from a liquid to a gas
  4. This gas is then passed through a heat exchanger into the heating system inside the building
  5. The heating system circulates the heat around the building through underfloor heating systems, radiators, and hot water tanks.

Types of Heat Pump

There are three types of heat pumps available:  

  • Air source heat pumps
  • Ground source heat pumps
  • Water source heat pumps

They all work in a similar way, but their main difference is where they draw their heat from. 

Let’s look at the three types. 

Air Source Heat Pumps

All air source heat pumps work by extracting heat from the outside air and transferring it indoors. There are two ways the heat can be transferred: either through a water-based system or an air-based system.  

Both systems can also be combined with a hybrid system – where the air source heat pump is used alongside a more traditional fossil fuel system such as a boiler.  

Let’s look at the three systems: 

  1. Air-to-water heat pumps
    Air-to-water heat pumps are the most commonly used heat pumps in the UK because they are suitable for many homes. As the name suggests, they extract heat from the outside air and transfer it into a water-based heating system – namely radiators, underfloor heating, and hot water tanks.
  2. Air-to-air heat pumps
    Air-to-air heat pumps extract heat from the outside air, just like an air-to-water heat pump. Instead of transferring the heat energy into a water-based heating system, the energy is transferred into an air heating system through vents or wall heaters. This heat pump system is often used in small properties, such as flats, and is ideal for replacing old electric systems such as storage heaters.
    An air-to-air heat pump doesn’t supply hot water, though. So, if one of these heat pumps is installed, a boiler or immersion heater for hot water will also be needed.
  3. Hybrid air source heat pumps
    All heat pumps are designed to deliver lower temperatures than traditional heating methods. That means radiators and hot water won’t get as hot as they would with a boiler, for example, and they take longer to heat up.
    So, a hybrid heat pump can be combined with an existing central heating system or boiler to give the heating or hot water a quick boost when it’s needed.

Other Things You Need to Know

What Size Heat Pump Do You Need?

Heat pump size is measured in kilowatts. Air source heat pumps can range from 5kW up to 16kW or more. Generally, the bigger the property you’re heating, the bigger the heat pump you’ll need. However, it also depends on other factors, such as how well the home is insulated, how many rooms it has and how many radiators there are. Calculating the correct size should always be carried out by a qualified heat pump installer.

Types of homeTypes of home ASHP recommended output (kW)GSHP recommended output (kW)
1-2 bedroom small home54
3 bedroom with poor insulation98
4 bedroom with efficient insulation98
4 bedroom with poor insulation1615
5 bedroom with efficient insulation1615

*Data in the above table is true to Screwfix’s knowledge at the time of writing.

How noisy are air source heat pump?

All air source heat pumps have an outdoor unit that contains a fan, so there will be some noise, and the volume will depend on the size of the pump and manufacturer. However, modern heat pumps shouldn’t make anything more than a low whirring sound.

How efficient are air source heat pumps?

Heat pump efficiency is measured as the Coefficient of Performance (CoP). This calculates the amount of inputted energy compared to the amount of outputted energy. So, if a heat pump uses 1kW of electricity to generate 4kW of heat, the CoP is 4. The higher the CoP, the more efficient the pump is. All air source heat pumps deliver more heat energy than the electrical energy they use, so they are typically very efficient to run.

Check out our range of air source heat pumps here.

Ground Source Heat Pump

Ground Source Heat Pump

Ground source heat pumps work by drawing heat energy from the ground through pipes filled with heat transference fluid and anti-freeze. The fluid circulates through the pipes then goes up into the heat pump located outside at ground level. The liquid is then heated and transferred into the home in the same way an air source heat pump works. 

Ground source heat pumps are more efficient than air source heat pumps. However, due to the more extensive work needed to install them, they tend to cost more. The pipes can be buried either vertically (digging to a depth of 150m) or horizontally (to heat an average-sized home, you’ll need an outside area that’s roughly the size of a tennis court, and the pipes would be buried at around 1m deep).  

For this reason, ground source heat pumps are better suited to new build homes so their installation can be planned into the construction process. 

Water Source Heat Pump

Water Source Heat Pump

Water source heat pumps work in a similar way to ground source heat pumps, but instead of drawing heat from pipes buried in the ground, the pipes are placed in a body of water. And instead of having a heat pump on the outside of the property, it’s placed inside.  

For this reason, a home will need enough room inside for the heat pump to be installed, and ideally, it will need to be in a room where its low hum isn’t going to annoy anyone. 

Water source heat pumps are often more efficient than air and ground source heat pumps because heat transfers better in water, and water temperatures tend to stay fairly stable throughout the year. 

However, the property needs to be very close to a large water source, such as a river or lake, and you need to be able to lay pipes between the water source and the property on land that’s within the property’s boundary. 

How Much Does a Heat Pump Cost?

When looking at the cost of heat pumps, it’s important to consider all the factors involved, not just the cost of the heat pump itself.

Let’s look at the costs in more detail:

  • Heat pump and installation costs
    The cost of a heat pump itself will depend on the brand, model, and size you need. You then need to consider the heat pump installation cost, which will vary from house to house.
    Generally, installing air source heat pumps will cost a lot less than ground source heat pumps because they are far easier to install. Whereas a ground source heat pump requires a lot of outside groundwork to bury the pipes into the ground.
    According to the Energy Saving Trust, an air source heat pump, including installation, can cost between £7-13K. That price rises to £20-30K for a ground source heat pump.
    But, as the government ramps up its efforts to phase out gas central heating, suggesting a ban on the installation of new boilers from 2035, the cost of heat pumps is expected to plummet over the coming years.
  • Government grants
    As reported in Which?, from April 2022, homeowners in England, Scotland, and Wales will be able to apply for a government grant of £5,000 to help towards the cost of switching to a heat pump. This £5,000 grant will bring the cost of air source heat pumps closer to that of a new boiler.
    Another scheme that rewards homeowners for switching to renewable energy is the Renewable Heat Incentive (RHI) scheme. People who join this scheme receive quarterly payments for seven years, based on the renewable heat they generate. It’s open to homeowners and private or social landlords in England, Scotland, and Wales.
  • Other costs
    Heat pumps generate lower temperatures than boilers or electric heaters, so you may need to consider the cost of other upgrades a home will need to make a heat pump system work efficiently.
    For example, radiators won't heat up to the high temperatures a boiler can generate and may need to be replaced with larger radiators to heat the home adequately. And, as well as the cost of the new radiators, you’ll need to consider the extra installation costs and potential disruption if floors need to be dug up to incorporate new pipes.
    There may also need to be upgrades to a home’s insulation because heat pumps aren’t very effective at heating poorly insulated homes.
  • Running costs
    As a rule, air source heat pumps are one of the most efficient ways to heat a home and cost less to run than more traditional heating systems. This is because they are run entirely on electricity, and they deliver more heat energy than the electrical energy they use.
    However, the running costs will vary from house to house, and depend on how well the home is insulated, the energy tariff and the temperature the thermostat is set to. The higher the temperature, the harder the unit will need to work, and therefore the more energy it will use.
  • Maintenance costs
    Air source heat pumps have a working life of around 15-20 years. And, just like boilers, they need to be professionally serviced. Usually, they need to be serviced every two or three years. But if the compressor is inside the home, they need to be serviced annually. The service cost will vary, but you can expect to pay in the region of £150-£200.

Savings From Heat Pump

It’s impossible to give an exact figure on savings from heat pumps because their running costs depend on so many varying factors, such as:

  • The electricity tariff
  • How the heat pump is operated
  • What system it’s replacing
  • The average air temperature of its location throughout the year

However, according to the Energy Saving Trust, while heat pumps need electricity to work, the amount of heat that is delivered to a home is more than the amount of electricity the heat pump uses to power its system. This should make them more energy-efficient than a boiler or other electrical heating system such as storage heaters.

What Are The Advantages of a Heat Pump?

  • They’re great for the environment – emitting zero carbon when used with a renewable electricity company
  • They’re a highly energy-efficient source for heating and hot water
  • They’re cheaper to run than other home heating systems
  • The installation cost can be offset by Renewable Heat Incentive payments
  • They’re low maintenance and can last for up to 20 years
  • They’re safer than gas boilers.

What Are The Disadvantages of a Heat Pump?

  • They’re more expensive to buy and install than gas boilers
  • A hot water cylinder is needed if you don’t already have one or a hybrid system to work with a combi boiler
  • A home needs to be well insulated for a heat pump to work efficiently.
  • Radiators may need to be replaced with bigger ones to achieve the same indoor temperature as a boiler or electric heaters.
  • Outside space is required for the heat pump to be installed.

Heat Pump Installation

Before considering if a heat pump is suitable for a home, the installer or an independent assessor should fully assess its energy performance. You’ll be issued with an Energy Performance Certificate (EPC), which will indicate whether the home is suitable for a heat pump or if extra upgrades will be needed.

Once you decide to go ahead, the heat pump installation should be carried out by a qualified tradesperson.

Can I install a heat pump to an existing heating system?

You can install a heat pump to an existing heating system. However, there are some important things to consider:

  • If the heat pump is replacing a boiler, the installer will need to check if the existing radiators will be large enough to emit enough heat. As heat pumps don’t heat to the same high temperatures, the radiators may need to be changed to larger ones, as will the hot water cylinder
  • If the heat pump is replacing a combi boiler, you’ll need to install a hot water cylinder to heat and store hot water or you’ll need a hybrid system that combines a heat pump with a combi boiler
  • The homeowner will need to learn how to use the new heat pump correctly. Boiler systems are used intermittently, whereas heat pumps are designed to run at lower temperatures for longer periods.

How do I install a heat pump?

Heat pumps should always be installed by a qualified heat pump installer, and we recommend you get at least three quotes. The installation process may vary slightly, depending on the installer, but in general, this is how the process works:

  • Inspection
    Your installer will start by inspecting the home where the heat pump will be installed. They’ll decide where the heat pump will be located, work out what size you need and advise on any upgrades required inside the property, such as larger radiators or adding or changing a hot water cylinder.
  • Installation outside
    First, the heat pump will be installed to the outside of the property. If it’s an air source heat pump, the installation will be fairly simple. But if they are installing a ground source heat pump, the work will be more extensive as it involves digging boreholes or trenches and burying pipes underground.
  • Installation inside
    Once the outside work is completed, the installers will move inside. They’ll disconnect the old heating system and connect the heat pump to the existing radiators, underfloor heating, and hot water cylinder. Work will be more extensive if they change radiators or electric heaters or add or change the hot water cylinder.

The installation time will depend on the work being carried out. But as a guide, an air source heat pump installation in a small property will take around one day, whereas a ground source heat pump installation could take three or four days.

You should also be prepared for a certain amount of disruption to the home. Particularly if the garden is being dug up for a ground source heat pump or if radiators or water tanks are changed.

Servicing Needs of a Heat Pump

Like a boiler, a heat pump will need to be professionally serviced from time to time to ensure it can run efficiently and prolong its lifespan. A well-maintained heat pump can last for up to 20 years or more.

Most heat pumps need servicing every two to three years. However, always check the manufacturer’s warranty as some need to be serviced annually.

Outside of the professional services, there are some things the homeowner can do to ensure the heat pump is kept working at its best, particularly during the autumn and winter months. For example, ensure leaves, debris, snow, or ice aren’t caught up in the fan’s grills and that plants are pruned back, so they don’t get too close to the pump.

5 Consideration When Getting a Heat Pump

We advise that anyone considering a heat pump should always do their research before deciding on what to buy to ensure it’s right for them, their situation and setup.

  1. Placement of a heat pump
    A heat pump needs to be installed outside the property at ground level on a flat concrete base. It needs to be at least one meter away from neighbouring properties and have plenty of space around it to ensure good airflow and easy access for maintenance.
    Heat pumps vary in size. An air source heat pump will be roughly the size of a washing machine, whereas a ground source heat pump is a little larger, depending on the size of the home it’s heating. The best place to locate a heat pump is usually on an outside wall of the house in the garden.
  2. Current heating system setup
    Heat pump costs, installation and other factors can be affected by the current heating system set up, so it’s very important to take these into consideration:
    ​​​​​​​If you currently have a combi boiler
    Combi boilers heat hot water on demand, and therefore there is no hot water cylinder in the home to heat and store water. So, if you switch to a heat pump, there are two options:
    - Install a hot water cylinder, bearing in mind that the cylinder will be very large, so you’ll need plenty of space for it.
    - Install a hybrid heat pump system so you can use the old system for hot water and the new system for heat.
    If you currently have radiators
    Heat pumps output heat at lower temperatures than boilers. This means:
    - You may need to upgrade to larger radiators, adding considerable cost to the project
    - You could install underfloor heating. It covers a larger surface area than radiators, it doesn’t need to run at high temperatures and is therefore highly compatible with heat pumps
    - You could install a hybrid system, where the old boiler is still used to give a heating boost when it’s needed or in very cold weather.
  3. House age and insulation
    For a heat pump to work efficiently, a home must be well insulated, so the heat generated doesn’t escape.
    Heat pumps are very well suited to new-build homes because they are built to the latest building regulations that ensure heat can’t escape through the roof, walls, windows or doors.
    However, older, poorly insulated homes can be problematic as a lot of the heat generated will escape. And as heat pumps run at lower temperatures than traditional heating methods, the pump will struggle to heat to the required temperatures. As a result, running costs will be high, and the home may feel cold.
    If you are considering fitting a heat pump to an older house, a qualified heating engineer will be able to advise you on what needs to be done to make it suitable for a heat pump. For example, it may involve upgrading loft insulation, adding cavity wall insulation, or installing double glazed windows.
  4. Requirement for a hot water tank
    Unlike a combi boiler, heat pumps can’t heat water on demand. So, if there isn’t a hot water cylinder in the building, you will need to have one installed, or you can install a hybrid heat pump to continue to use a boiler for hot water only.
  5. Planning permission needed for a heat pump
    Before installing a heat pump, it’s essential to check if you need planning permission. In most cases, a heat pump is considered a ‘permitted development’, meaning no planning permission is required. However, if you live in a listed building or conservation area, you may need planning permission. But whatever your circumstances are, it’s always best to check.
    The Energy Saving Trust advises that you also must inform your local district network operator (DNO) that you are installing a heat pump. This is the company responsible for bringing electricity to the home. You can ask your installer to do this for you as they have all the information required for filling out the forms.
    In summary
    Installing a heat pump is a significant investment, and it’s important to ensure you have all the facts available to make an informed decision about the best type of heat pump to install and how they work. But once installed, a heat pump is an excellent investment due to its long lifespan, reduced running costs and environmental benefits.
    If you’re considering installing a heat pump, check out our range here.

FAQs on Heat Pumps