Air source heat pumps (ASHP’s) are appliances that must be installed on the outside of a home or building to work and can often be similar in looks and size to a commercial air conditioning unit.
Understanding the size of an air source heat pump can be important for both the installer and the end user in terms of output capacity, aesthetics and how well it can be hidden out of view around a home.
The size of an air source heat pump can typically be up to 3 ft (1m) wide, 3ft (1m) high and 1ft (300mm) in depth. However, the actual size of any installed air source heat pump can vary from this depending on factors such as the internal space that needs to be heated, and the brand and model of heat pump.
Our own air source heat pump is a dual fan unit that is sized correctly to be able to heat our 5-bedroom house.
We discuss below more about the size of our heat pump and the factors that would affect the size of an air source heat pump to be installed.
How Big Is An Air Source Heat Pump?
The size of an air source heat pump can vary between installations, but can you expect a standard size heat pump to be up around 3ft (1m) in height and width and around 1ft (300mm) in depth.
However, this is just an average size, and many heat pump units will be smaller or bigger in overall size or be shorter or longer in either length width or depth.
As an example, our air source heat is a taller sized unit and has the dimensions of:
- Height – 1.35m (4.4ft)
- Width – 1.02m (3.35ft)
- Depth – 0.33m (1.1ft)
This unit is sized appropriately for the size of our house and so installers may choose different sized unit depending on the size house or building you need to heat, the type of air source heat pump and the manufacturer of heat pump that they go with.
Our air source heat pump is mounted directly onto the ground and space has been left behind the unit to the house to allow for the pipework.
For size reference, the image below shows a comparison between the size of our air source heat pump and the smaller domestic air conditioning unit sat next to it.
See our article comparing air source heat pumps against air conditioning for more information.
An air source heat pump won’t be the only component you need as apart part of the whole heating system.
If looking to use an ASHP to provide central heating and domestic hot water, you’ll need a range of apparatus inside the home or building for hot water storage and distribution.
Pipes head through our garage from the air source heat pump outside to a cupboard in the utility room.
It’s in this cupboard where our hot water storage tank/water heater is located along with all the other apparatus.
See our other articles on using an air source heat pump with a hot water tank and using an air source heat pump to provide domestic hot water for more information.
Therefore, understanding how much space is required for all the ancillary equipment that must accompany an air source heat pump can also be just as important as installing the right size of heat pump, and in the right location.
While our heat pump is the air to water type used for central heating and hot water, air to air heat pumps can need a series of ducts through a home to distribute warm air.
For air to air heat pump installations, inside a house will be an air handler whose job is to distribute the air. These appliances can have evaporator coils and a fan to blow the air towards the house. Unlike outdoor units, an air handler can be smaller.
On average, a wall-mounted air handler can be 12x32x9 inches (30.48 x 81.28 x 22.86 cm), though this is not always the case. Depending on the design and needs of your house, one air source heat pump can have multiple air handlers placed in different locations of a house.
What Size Of Air Source Heat Pump Do You Need?
The size of an air source heat pump will typically be proportional to the output capacity of the unit required to serve the size of home, measured in kW. Often ranging from 6Kw to 15kw, the more powerful the unit, the bigger in size it typically is.
Choosing the right-sized heat pump for a home can be one of the most important aspects of the installation process.
If an air source heat pump is too large for a house, it can short cycle or shut off too often, leading to wear and tear.
If a heat pump unit that’s too small is chosen, it won’t be able to effectively heat or cool the house, and if it does, more energy will be required and potentially lead to a shorter life span.
It’s therefore important to always consult a certified, experienced heat pump installer with intricate design software to gauge the size accurately.
This is not something you should attempt to do yourself because it can be the difference between a well-functioning heat pump and an inefficiently performing one.
The output capacity of an air source heat pump, and therefore its size, will be dictated by several factors, which we discuss in more detail below.
Factors Affecting The Size Of An Air Source Heat Pump
Size Of Property
Generally speaking, the bigger your home, the bigger the heat pump unit will be.
Besides the size, the installer will consider your property type as well. A maisonette, for example, will require a bigger heat pump than a bungalow. The size of your rooms will also impact because some rooms like lounges are heated for longer periods than others.
Level Of Insulation
Heat loss can be a concern when installing an air source heat pumps because they won’t be able to provide the same instantaneous heat as conventional boilers/furnaces.
A key consideration in heat pump sizing is the level of insulation in your home. If it’s poorly insulated, heat can escape more easily and so you need a more powerful heat pump to compensate.
A home with a high level of insulation can afford to have a heat pump with a lower output.
Your installer will require a current Energy Performance Certificate to know the potential energy efficiency before installing the unit.
Our ASHP was installed as part of the construction of the house and so modern insulation requirements meant that it could be kept as small as possible.
Your Location
Different locations can have different seasonal temperatures, which must be considered when selecting heat pump size.
An installer will consider the coldest air temperature of the year in your location and choose a system accordingly. Typically, warmer locations can help reduce heat pump size.
The Heating System Used
The heat distribution system your home use can affect how much heat gets released.
For example, underfloor heating/radiant floors can run at a much lower temperature, whereas radiators require higher temperatures but can be compromised with larger surface areas.
When picking a size for your home, know that radiator systems need to be bigger than their underfloor counterparts.
Our home uses a combination of underfloor heating and large and numerous radiators to help keep the house warm.
ASHP Size Calculator
While there’s no perfect size calculator for heat pump sizes, here is one way to get you a close figure.
Multiply the size of your home (in meters squared) by how many kilowatts (kW) are needed to heat your home comfortably.
Roughly, experts recommend 1kw per 10 meters squared (107.63 square foot), though the amount of heat loss in your home is also considered. Consider that a new house loses around 50kw, while an older one loses as much as 100kw.
Again, the location of your home matters. If you’re in the US, find out the climate zone of where you live on the table below and multiply that with the square foot of your home to get the recommended size in tonnage.
| US Climate Zone | BTU per square foot |
| Zone 1 | 30-35 BTU/ sq.ft |
| Zone 2 | 35-40 BTU/sq.ft |
| Zone 3 | 40-45 BTU/sq.ft |
| Zone 4 | 45-50 BTU/sq.ft |
| Zone 5 | 50-60 BTU/sq.ft |
With these figures and the help of software, your installer will be able to recommend the right size of air source heat pump for your home. This perfect size should provide enough heat during winter (and potentially hot water) and also cool your home perfectly during summer if required.
As an example, our 5-bedroom home is powered by an air source heat pump a capacity of 11.20kW.
See our dedicated article on what size air source heat you need for more information.
How Big Is An Air Source Heat Pump?
The average size of an air source heat pump can around 3ft (1m) high and wide, and approximately 1ft (300mm) in depth.
However, the actual size of air source heat pump required can vary between each installation and can be down to several factors including the size of the property, the existing heating setup, the climate, and the level of insulation in the property.
A certified installer will be able to provide an accurate size of air source heat pump required.
Further Reading
Air Source Heat Pumps Explained
How An Air Source Heat Pump Works
Parts Of An Air Source Heat Pump Explained