Purchasing the correct size heat pump is vital to ensuring the efficiency of your unit as well as your comfort. Use the following steps and information to help you choose the best size heat pump for your needs.

In general, the larger the house the larger the heat pump you will need. Size is calculated in tons, with one ton of cooling capacity being equivalent to the ability to remove 12,000 British Thermal Units (BTUs) of heat per hour. A typical UK home requires between two and four tons of cooling capacity.

You will also need to take into account the location of your home. If you live in an area with a warmer climate, you will likely need a larger heat pump than if you lived in a cooler climate.

Another factor to consider is the level of insulation in your home. If your home is well-insulated, you may be able to get away with a smaller heat pump than if your home has poor insulation.

Once you have considered all of these factors, you can use our heat pump size calculator to determine the correct size heat pump for your needs.

Type of property

The size of a heat pump for a new house is straightforward to figure out since, in order to meet building rules in the UK, houses must be built with particular amounts of insulation.

The degree of heat loss was assessed carefully at the planning stage, so the size of the heat pump can usually be reasonably predicted. Calculating heat loss in older dwellings is more difficult, so a heat load calculation should be carried out by a qualified heating engineer.

This will take into account the heat that escapes through the fabric of the building, any solar gain, and the amount of heat required to maintain comfortable indoor temperatures.

One kilowatt of heat is required for heating every 10 square meters of your home. As a result, if you want to heat a 100-square-meter house, you’ll need a 10 kWh boiler.

If your house only uses the heating for part of the year, you’ll need to convert this figure into BTUs.

For example, in a UK winter where outside temperatures are around 7 °C and indoor temperatures average 21 °C, 10 kWh would be equivalent to 34,121 BTUs.

Climate

The climate in your area will also affect the size of heat pump you need. In cooler climates, a smaller unit may be all that is required to maintain comfortable indoor temperatures. However, if you live in a warmer climate, you will likely need a larger heat pump to achieve the same results.

As a rule of thumb, for every one degree Celsius (1.8 degrees Fahrenheit) that the average temperature drops below 18 degrees Celsius (64.4 degrees Fahrenheit), you will need an additional kilowatt (kW) of heating capacity. So, if the average temperature in your area is 15 degrees Celsius (59 degrees Fahrenheit), you would need an additional 3 kW of heating capacity. This is equivalent to 10.5 BTU/hr.

Insulation

The level of insulation in your home will also affect the size of heat pump you need. If your home is well-insulated, you may be able to get away with a smaller heat pump than if your home has poor insulation.

As a rule of thumb, for every one square metre (10.7 square feet) of exposed external walls, you will need an additional 0.1 kW of heating capacity. So, for example, if your house has 30 square metres (323 square feet) of external walls, you would need an additional 3 kW of heating capacity. This is equivalent to 10.236 BTU/hr.

Air source heat pumps

An air-source heat pump may be used to heat either the air or water in a home. An air-to-air heat pump heats the property with a network of fans surrounding it, as well as provides cooling during the summer.

If you currently have a boiler installed, then air to water heat pump can be used as a replacement. This type of heat pump heats water which is then circulated around the property using the existing radiator system.

Ground source heat pumps

A ground source heat pump is usually used to heat water, which is then circulated around the property using the existing radiator system.

A ground source heat pump uses buried pipes, called a ground loop, to extract heat from the ground. The ground loop is made up of a series of coils of plastic pipe, through which a mixture of water and antifreeze is pumped.

The size of the heat pump you need will depend on the type of property you have. It also implies that they take up a lot more space and are only suitable for use in a home with a large garden.

Do You Have Radiators Or Underfloor Heating?

More and more people are having underfloor heating installed in their homes as it is seen as a more efficient way of heating a property.

Underfloor heating heats the whole floor area evenly, so there are no cold spots.

Radiators, on the other hand, tend to heat the air around them, which can create cold spots.

If you have underfloor heating, you will need a larger heat pump than if you have radiators, as it will take longer to heat the floor area.

As a rule of thumb, for every 100 square metres (1,075 square feet) of floor area, you will need one kilowatt (kW) of heating capacity.

So, for example, if your house has 200 square metres (2,152 square feet) of floor area, you would need a 2 kW heat pump. This is equivalent to 6.8 BTU/hr.

This can be calculated properly by a professional MCS installer who will come and assess your property to give you an accurate heat pump size.

Number of rooms

The number of rooms in your property will also affect the size of the heat pump you need.

If you have a large house with many rooms, you will need a larger heat pump than if you have a small house with fewer rooms.

As a rule of thumb, for every room in your property, you will need 0.1 kW of heating capacity. So, for example, if your house has 10 rooms, you would need a 1 kW heat pump. This is equivalent to 3.4 BTU/hr.

This can be calculated properly by a professional MCS installer who will come and assess your property to give you an accurate heat

How Many People Live In Your Home?

The number of people living in your home will also affect the size of the heat pump you need.

The more people there are in a home, the more heat will be generated, and this will require a larger heat pump to maintain comfortable indoor temperatures.

As a rule of thumb, for every two people living in a property, you will need an additional kilowatt (kW) of heating capacity. So, if there are four people living in a property, you would need an additional 2 kW of heating capacity. This is equivalent to 6.8 BTU/hr.

How Much Does a Heat Pump Cost?

The Energy Saving Trust predicts that a regular air source heat pump installation will cost between £6000 and £8000, whereas a ground source heat pump system will set you back between £10,000 and £18,000.

Is it worth it?

Given that you may receive up to £9,100 from the Domestic Renewable Heat Incentive (RHI) for an air source heat pump and over £27,000 for a ground source system, it is definitely something to consider, especially if you are looking for an environmentally friendly way to heat your property.

What About Maintenance Costs?

Heat pumps require very little maintenance and can last for many years with minimal servicing. In fact, the only real maintenance you will need to do is to keep the outdoor unit clear of leaves and debris, as this can obstruct airflow and reduce efficiency.

You should also have your heat pump system serviced by a qualified engineer every few years to ensure it is running efficiently. This will usually cost in the region of £150+VAT.

Is There A Heat Pump Size Calculator?

Since houses come in all different shapes and sizes, there is no one size fits all answer when it comes to heat pump size.

The best way to find out the perfect heat pump size for your home is to get a professional MCS installer to come and assess your property.

They will be able to give you an accurate heat load calculation, which takes into account all of the factors mentioned above.

This will ensure that you get the right size heat pump for your needs and that you are not paying over the odds for heating capacity that you do not need.

Professionals recommend one kilowatt for every ten square meters, but the amount of heat your home loses must also be taken into account.

This will need to be determined by a specialist, but on average, a new house will lose 50 kW while an older house with little or no insulation might lose as much as 100 kW.

How Much Money Could A Heat Pump Save You?

When compared to an existing heating system in a four-bedroom detached house, for example, a standard air-source heat pump might save you money and reduce CO2 emissions.