Heat Pump Sizes: What Size is Right for My House?

The right heat pump can provide significant savings over a traditional gas boiler. In addition to lower monthly running costs, the government is now offering households a grant of up to £5k to purchase and install specific heat pump systems. Now may be an excellent investment if you are considering upgrading your home’s heating system.

That being said, while a new heat pump may reduce your energy bills, you’ll need to consider several things, such as the size of your home, to choose the right heat pump for the best results. This helpful guide will teach you how to properly size a heat pump for your home.

Calculating Heat Pump Size – What You Need to Know

Determining the right heat pump size for your house :

Size of Your Home

More significant properties generally require a larger-sized heat pump but determining the heat pump size for your home or any property isn’t so cut and dry – the type of property you have and the size of the rooms must be considered. A detached house is likely to have different heating needs than a countryside cottage or even a terraced house with smaller rooms.

Different rooms or areas will also have different heating needs regardless of your home type. For example, you may want your bathroom to remain warm throughout the day but only heat the bedrooms during the evening and morning hours.

A reputable, accredited heat pump installer will take all of this and more into account when recommending the ideal heat pump size for your home.

Generally, a 4kW-12kW heat pump is sufficient for most homes. However, that’s quite a gap. Here’s a cheat sheet showing the recommended heat pump output for a few of the most common home types here in the UK:

Two-bedroom house or flat – 5 kW
Three-bedroom detached, semi-detached, or terraced house – 9 kW
Four-bedroom detached house – 16 kW

*Please note: These outputs are for homes with older insulation. The quality of your home’s insulation and other factors should also be considered when determining your house’s ideal heat pump size.

Property Type

For a new build house, the size of the heat pump should be easy to calculate, given insulation standards. Therefore, the heat loss level can be accurately calculated during the design stage.

However, this isn’t the case with older houses built before the 21st century. Before undertaking a heat loss assessment, a detailed property survey is required for these homes. During the assessment, a heat pump installer will examine the following:

Number of rooms
Types of rooms
Insulation quality and thickness
Whether the property uses radiators or underfloor heating
Seasonal temperature fluctuations
Desired indoor temperature.

The number and different types of rooms are significant considerations. Not only does the number of rooms add to the total size of the house, but some rooms require different heating levels than others. The number and types of rooms are calculated to determine a home’s overall heat demand and the needed heat pump size.

Homes often have heat pumps ranging in size from 4 kW to 12 kW. Bigger heat pumps can also be installed if needed, but this is usually only the case for substantial properties, district heating installations, or shared heat pump systems.

Insulation Quality

Another critical consideration when sizing a heat pump for your house is determining how well it is insulated. Since the water used in a heat pump remains at a lower temperature than in a traditional gas boiler, any heat loss will impact the heat pump’s operating efficiency.

To comply with UK building codes, newer builds must adhere to higher insulation standards. As a result, 4 kW, 5 kW, 6 kW, and other lower output heat pumps can be used. While heat pumps can still be installed in older properties, they must meet specific minimum insulation levels.

If your house does not meet the minimum insulation requirements, improvements to the insulation must be made to bring it up to code. You may be eligible for the boiler upgrade scheme. To qualify, you are required to provide an Energy Performance Certificate or EPC. An experienced heat pump installer can identify any potential problems regarding your home’s energy efficiency.

The energy efficiency of a property will affect the required heat pump output size. If your home is well-insulated, has double-glazed windows, and does an excellent job of retaining heat, a lower-output heat pump should be more than capable of meeting its heating needs. On the other hand, a higher output heat pump will likely be required if your home needs to be better insulated and prone to losing heat.

Radiators vs. Underfloor Heating

Output size is affected by more than the size or type of property you have. To correctly size your heat pump, an installer will also consider your home’s heat delivery system.

An air source heat pump warms the water to a lower temperature than a traditional boiler. Consequently, it requires more surface area to heat your home and keep it feeling nice and warm.

While radiators, for the most part, work fine with gas boiler systems, they lack the surface area needed for heat pumps to work efficiently. Therefore, homes with radiators require larger heat pumps with higher power outputs.

Underfloor heating systems, however, are ideal for heat pumps. Homes with underfloor heating can use smaller heat pumps with lower power outputs, resulting in lower installation and monthly operating costs.

Type of Heat Pump

When sizing a heat pump, you must also account for the specific type of system you are considering.

Ground Source Heat Pumps

When installed correctly, ground source heat pumps provide reliable, year-round heating consistency.

A new detached house around 200 square metres in size requires an 8 kW ground source heat pump system, while a smaller 100 square metre terrace house should only require a 4 kW unit. The outdoor climate and weather play little to no role in the performance of a ground source system.

Air Source Heat Pumps

In colder climates, air source heat pumps work less efficiently and produce less power. In other words, they are less consistent and struggle to keep up. If you go with an air source heat pump (ASHP) over a ground source heat pump (GSHP), you will likely need an extra 1 kW of power to heat the same house.

Where You Live?

No two places in the UK experience the same weather conditions. Eastern areas, like Canterbury, receive up to 10 hours of sunshine each day, while residents of Lancaster up in the northwest only average 2.2 hours of sun daily.

Where you live in the UK will significantly impact the outside temperature and the size of the heat pump your house will need, especially if you go with an air source pump. The colder and less sunny climate will also play a part in the size of the air source heat pump.

That said, air source heat pumps have been known to work well in temperatures as low as -25º C. Since UK weather rarely dips below 0ºC, you should be in good shape regardless of which type of heat pump you use.

When calculating your heat pump size, your installer must still factor in your area’s lowest annual temperatures.

Why Does the Size of Your Heat Pump Matter?

The output of your heat pump should match your household’s heating needs. A heat pump with too high of output for your home’s heating demands will turn on and off frequently. This is known as short cycling, and in addition to producing higher energy bills, it can also place unnecessary strain on the pump and lead to premature breakdowns and repairs.

Conversely, a heat pump with a higher rating will work inefficiently and may not be able to warm your house sufficiently. It will run for more extended periods, which may also lead to higher energy bills and the need for repairs.

Finding the Best Heat Pump for your Home

There are several factors to consider when deciding on a heat pump size for your home. Although there is a standard to tell you the exact heat pump size needed for your house, an accredited heat pump installer will factor everything above to calculate your home’s heat loss and specific heating needs.

Visit a Sustainable Homes Centre

Viva Training, based in Halifax, has become West Yorkshire’s first Sustainable Homes Centre (SHC), partnering with leading heat pump manufacturer, Daikin, to provide a ‘hub’ for installers, developers and consumers looking to find out about, purchase and/or train in heat pump installation.

From homeowners looking to save money on their fuel bills and ‘go green’ to heat pump installers wanting to train and take advantage of the opportunities presented by a low-carbon future, the Sustainable Centre at Viva will provide an important ‘heat pump hub’ for the area.

To visit Viva’s Sustainable Centre in Halifax, please contact hello@vivatraining.co.uk or call 0800 6123177 to make an appointment.