What size heat pump do I need?
Deciding to make the switch away from a traditional gas boiler to try an alternative heating solution can feel daunting. People generally like to stick with what they know, perhaps worried that learning a new system will be difficult or fiddly. But, as with any system, once a heat pump is set up, you don’t even need to think about it - all of your heating and hot water needs will be met.
But the big question we get asked time and again is ‘What size heat pump do I need?’. Deciding on the right size can feel like navigating an ocean - you get confused, lost and stuck before simply going round in circles. We consider ourselves the heat pump experts, and that’s why we’re here to help you decide what size is most suitable for your home.
Summary of topics:
Why is heat pump size important?
As with a boiler, it’s imperative that you get the heat pump size right. One that’s too small may not provide the heating requirements you need and one that’s too big might use too much energy that is ultimately wasted when it isn’t used. This can be costly in the long run and could actually reduce the lifespan of your heat pump.
An unnecessarily big heat pump will also run in short cycles, which is bad news for the machine's motor, and may mean you have to replace the heat pump before its usual 20-year lifespan.
It isn’t always just the size of your home that determines how big your heat pump should be. Other factors include how good your insulation is, how quickly heat is lost from your home, the number of radiators there are and the temperature you want your home to be. All of these things could impact how big or small the pump needs to be.
How to choose the right size air source heat pump
When your home is initially inspected by a qualified heating installer, they will determine what size air source heat pump you need.
If you live in a new build property, the inspection may take less time and will probably be less complex. This is because new builds generally have more insulation and are made to a more efficient specification because of UK building regulations. These regulations were different in the 90s and beyond, so older homes generally aren’t as efficient.
If you have an older property (older than 2000), you may require a building survey that is completed by a building surveyor. These will detail and assess the heat loss of your property, and take this into account when sizing a heat pump.
Heat pumps are sized by heat output in kilowatts (kW). To get a general idea, you can use the table below to see what size heat pump each type of property might need, though this could be subject to change.
Property type/size | Insulation quality | Heat pump size | Recommended heat pump |
|---|---|---|---|
2/3-bedroom house | Average/good | 5kW | |
3-bedroom house | Poor | 8kW | |
3/4-bedroom house | Average/good | 8kW | Vitocal 200-A |
4-bedroom house | Poor | 10kW | Vitocal 200-A |
5/6-bedroom house | Average/good | 16kW | n/a |
Large office and commercial buildings | n/a | 32kW+ |
An unnecessarily big heat pump will also run in short cycles, which is bad news for the machine's motor, and may mean you have to replace the heat pump before its usual 20-year lifespan.
It isn’t always just the size of your home that determines how big your heat pump should be. Other factors include how good your insulation is, how quickly heat is lost from your home, the number of radiators there are and the temperature you want your home to be. All of these things could impact how big or small the pump needs to be.
How to choose the right size air source heat pump
When your home is initially inspected by a qualified heating installer, they will determine what size air source heat pump you need.
If you live in a new build property, the inspection may take less time and will probably be less complex. This is because new builds generally have more insulation and are made to a more efficient specification because of UK building regulations. These regulations were different in the 90s and beyond, so older homes generally aren’t as efficient.
Property type/size | Insulation quality | Heat pump size | Recommended heat pump |
|---|---|---|---|
2/3-bedroom house | Average/good | 5kW | |
3-bedroom house | Poor | 8kW | |
3/4-bedroom house | Average/good | 8kW | Vitocal 200-A |
4-bedroom house | Poor | 10kW | Vitocal 200-A |
5/6-bedroom house | Average/good | 16kW | n/a |
Large office and commercial buildings | n/a | 32kW+ |
If you have an older property (older than 2000), you may require a building survey that is completed by a building surveyor. These will detail and assess the heat loss of your property, and take this into account when sizing a heat pump.
Heat pumps are sized by heat output in kilowatts (kW). To get a general idea, you can use the table below to see what size heat pump each type of property might need, though this could be subject to change.
How to choose the right size ground source heat pump
As with an air source heat pump, your home will be initially inspected by a qualified heating installer to determine what size ground source heat pump you need. These appliances are generally better suited to larger homes that have a bigger amount of land, however, they can be fit in smaller properties too.
The pipes that are laid in the ground can be installed vertically or horizontally, which is ideal if you have an average-sized garden.
Property type/size | Insulation quality | Heat pump size | Recommended heat pump |
|---|---|---|---|
2/3-bedroom house | Average/good | 5kW | Air source (see above) |
3-bedroom house | Poor | 8kW | Air source (see above) |
3/4-bedroom detached house | Average/good | 7.5kW | |
4-bedroom house | Poor | 10.4kW | Vitocal 200-G |
5/6-bedroom house | Average/good | 10.4kW | Vitocal 200-G |
Large office and commercial buildings | n/a | 32kW+ |
Other considerations
Other things that could impact the size of your heat pump include:
Whether you have radiators vs. underfloor heating
Outside space
Average outside temperature (this differs depending on where in the UK you live)
The number of bathrooms you have
The demand for heating/hot water
What type of heat pump should I consider?
Ground source heat pump
The pump’s name explains where it takes its heat from. A ground source heat pump collects natural energy from the ground around your home via pipes that are laid specially. Within these pipes is an antifreeze solution. As the solution moves through the pipes, it gathers heat and carries it back to your heat pump. Here, the heat is transferred via a heat exchanger to a refrigerant; this is then compressed to increase its temperature further so that it can be used to heat the water that will be pumped around your home’s radiators.
This type of heat pump is good if you have a decent amount of land around your home. When it’s installed, the pipework needs to be laid at a depth of around one metre, but this is where installation can get messy. If your garden is mostly grass, then this won’t be a problem as new grass can be put down. However, if your garden is mostly patio, then it may be difficult to install the heat pump.
If your garden is a little on the small side, the pipes can be arranged vertically instead. This means that instead of installing them a metre below the surface, boreholes can be drilled up to 150 metres deep. This ensures the pipes still have a large enough surface area in which to gather heat before taking it into your home.
If you live in a city, then this option might be completely off limits to you, and you may need an air source heat pump instead.
Air source heat pump
An air source heat pump takes in heat from the air outside in order to warm up your home. These appliances work in a similar way to ground source heat pumps in that a refrigerant collects the heat and is then compressed to increase its temperature.
The two types of air source heat pumps are air to air and air to water.
An air to water heat pump works in a similar way to a boiler, in that the water is heated and pushed around your radiators. In this way, the heat is taken from the air and transferred to the water. In an air to air heat pump, heat from outside is taken in in the same way, but it is blown directly into the home via fans. These systems can be reversed so that they cool your home in summer by removing the humidity and heat from the air and carrying it outside.
Air source heat pumps are easier to install than ground versions as there’s less mess. They also often take less time to install, reducing labour costs. They’re better suited for people with less surrounding space or who are on a tighter budget.
Water source heat pump
A water source heat pump takes the heat from a surrounding water source, however there are some specific requirements that should be followed if you want your water heat pump to work as efficiently as possible. The water source needs to be large enough so that it doesn’t freeze (remember, the anti-freeze solution will be taking heat away from the water, potentially cooling it down to the point of freezing over).
The closer the source is, the better, otherwise the system may need to use a lot of electricity to carry the anti-freeze a long way to get to and from your home. The other thing to consider is the height of the water source compared to your home. If it’s located too high up, the system may struggle to carry the solution around the circuit.
A large water source is imperative for this kind of system to work along with any required authorisation from planning or environment agencies. If you live in a town or city with no large lakes or rivers nearby, you should consider an air or ground source variety instead.
We have tons of information about heat pumps across our site. Below are just a few guides to get you started:
