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What Size Air Source Heat Pump Do I Need? Outputs & Dimensions

Nick Geary
By: Nick Geary
Updated: 20th April 2022

What Size Air Source Heat Pump Do I Need?
When having a new air source heat pump installed, a question you should ask yourself is "What Size Air Source Heat Pump Do I Need?". This question actually refers to two types of 'size' you need to consider with heat pumps: their output size and their physical dimensions.

What is output size?

The output size of an air source heat pump is the amount of energy in kW it requires to run. This is usually dictated by the size of your home and how energy efficient it is. The larger your property, the higher the output you will need.

What affects output size?

Output size is not only affected by the size of a property. It is also dependent on what kind of heating systems are installed. Properties with underfloor heating or low temperature radiators, will be capable of running on a low temperature air source heat pump with a lower output requirement. However, properties with traditional radiators will require a high temperature heat pump to fulfil their heating requirements.

A property's energy efficiency will also affect what output size is required. If your home has ample insulation, double-glazing and retains heat well, a heat pump with a lower output will be capable of meeting your home's heating needs. However, if your home is not well-insulated and loses a lot of heat, a heat pump with a higher output will be required.

Typical output requirements

Following some industry research, we created the table below to provide a rough idea of what output sizes are typically required for different types of properties.

Property type Recommended output
1 bed flat/apartment 2.5 – 3kW
2 bed house 3 – 5kW
3 bed house 7 – 9kW
4 bed house 9 – 12kW
5 bed house 12 – 16kW
High temperature pump for traditional radiators 14 – 18kW
Note: All figures are dependent on the energy efficiency of the property and are only a rough guide

To get the right size of air source heat pump for your home, we highly recommend consulting a heating engineer. You can get free comparison quotes from up to 3 local heating engineers by clicking the link below.



How much space do I need?

Depending on the type of heat pump you want, what size output you require, and whether you have an existing hot water storage tank, you'll need a certain amount of outdoor and indoor space available to install a new air source heat pump. One of the biggest choices you'll need to make will be whether you get a split or monobloc heat pump.

How big is a monobloc pump?

Small monobloc heat pump sizeMonobloc heat pumps only take up space on the outside of the property. How much space a monobloc unit will need depends on its output, which directly affects the unit's dimensions. For example: If you live in a 2 -3 bed house, you will require a monobloc heat pump with an output of 5 – 9 kW. The average dimensions of one of these is: 1,200mm wide, 930mm high, and 370mm deep.

Large monobloc heat pump sizeHowever, if you live in a 4 – 5 bed house the 12 – 16kW unit you'll require will be bigger, with average dimensions of: 1,130mm wide, 1,475mm high, and 430mm deep.

If you have enough space for a larger unit outside, a monobloc heat pump may be your best option. However, you will need a separate hot water storage tank installed to allow for hot running water. We have compared monobloc and split heat pumps in more detail in this article: Monobloc vs Split Air Source Heat Pumps: Which is Best?

How big is a split heat pump?

Split heat pump small outdoor unit sizeSplit heat pumps generally have smaller outdoor units than monobloc pumps, but have an indoor unit too. The size of the outdoor unit will most likely be linked to the required output too. For a 2 – 3 bed house with an output requirement of 5 – 9kW the average dimensions of a split heat pump outdoor unit is: 1,000mm wide, 790mm high, and 405mm deep.

Split heat pump large outdoor unit sizeFor a 4 – 5 bed house with an output requirement of 12 – 16kw, the average dimensions of an outdoor unit are: 1,000mm wide, 1,415mm high, and 385mm deep. While this is bigger, it is still smaller than a monobloc outdoor unit.

There is the size of the indoor unit to consider though, and these can range vastly, depending on what kind of indoor unit you need.

Do you have space for a separate hot water tank?

Split heat pump indoor unit size wall mountedThe size of an indoor unit depends on whether you have space to install a separate hot water storage tank to allow for hot running water. If you do, then having a smaller wall unit installed would be the best option. These smaller indoor units have average dimensions of: 495mm wide, 900mm high, and 345mm deep. This is not dissimilar to the average dimensions of a combi boiler.

Split heat pump indoor unit size floor standingIf you don't already have a hot water storage tank and don't have the space to install one separately from your indoor unit, you could get a split heat pump with a free-standing indoor unit with an integrated hot water storage tank. The average dimensions of these are much bigger than a wall unit, as they require extra room for the integrated tank: 600mm wide, 1,825mm high, and 685mm deep. The amount of space these units require is equivalent to needing room for a second fridge freezer in your home.

How do I get the right heat pump?

As there's no one-size fits all solution to choosing the right heat pump for your home, we highly recommend getting professional advice from a local heating engineer. Fortunately, we can help you with finding one at the best possible price. Click the link below and we'll find you quotes from up to 3 air source qualified heating engineers in your area. All you need to do is pick which one you'd prefer to use.



Nick Geary

About the author

Nick Geary

Nick has a wide range of experience writing about conventional and renewable heating solutions, and is always increasing his knowledge by researching any new heating technologies on the horizon.

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