Air source heat pumps are becoming more common heating appliances in households, and extract heat energy from the air to heat homes; increasing energy efficiency while helping to decrease carbon footprints.
Despite the benefits that an air source heat pump can bring, they’re not always suitable for all homes and there can be several requirements that a home must meet to accommodate an air source heat pump.
Air source heat pumps require outdoor installation on a flat surface in an area with sufficient airflow. They must also meet climate and power supply requirements, and a home’s existing internal heating setup must be appropriate to work with a heat pump.
Each type of air source heat pump system can have different installation requirements and each specific install can differ, but there are a general set of installation requirements that typically need to be followed in order for a heat pump system to ultimately work as efficiently as possible.
Our air source heat pump heating and hot water system was installed when our house was built and so we understand the installation requirements for these types of appliances.
This article examines in depth aspects to consider before choosing and installing an air source heat pump. Additionally, we look at the two main types of air source heat pump systems to help you choose one that’s suitable for your home.
Air Source Heat Pump Installation Requirements
Air source heat pumps (ASHPs) work differently to other more traditional types of heating systems in that there’s no combustion of fuel to generate heat; where heat production can be almost instantaneous but may not be the most efficient or environmentally friendly.
Instead, air source heat pumps move heat from one place to another. In this case, heat stored naturally within outside air is captured to be used to heat the air inside a home and raise indoor temperatures.
As part of an air source heat pump system, an external air source heat pump unit will be located outside a home and used to extract the heat from the air.
This external heat pump unit needs to be in the right location outside a home or airflow can be compromised and a heat pump can be working less efficiently than designed. There are also noise considerations at installation.
ASHPs can’t generate the same instantaneous heat that other conventional heating systems can and so need to be used for longer periods of time to reach the same desired indoor temperatures.
The internal heating apparatus therefore also needs to be of a sufficient standard to be able to work with how a heat pump delivers heat.
There are therefore a number of installation requirements for air source heat pumps to help ensure that they work as effectively as possible, which include:
- An adequate location for the external heat pump unit
- Consideration of the local climate and the choice of heat pump system
- Choosing between a traditional or split system
- Ensuring an adequate internal heating system is used to work alongside a heat pump
- Within reaching distance of a power source
- Any other structural requirements
We discuss each of these main points in more detail below using our own air source heat pump as an example.
The main part of an air source heat pump system can be considered to be the external air source heat pump unit that sits outside of a home.
This heat pump unit is where heat is extracted from air that’s forced through it using fans.
To install this air source heat pump unit you’ll therefore need to have a suitable location in which to place it.
It requires an easily accessible flat area with sufficient airflow, that may also need to consider factors such minimizing time in sunlight and staying out of areas that could experience high winds.
The manufacturer of a heat pump will outline the specific requirements for installation. The requirements from the manufacturer of our own heat pump are shown as an example below.
Our article on where to install an air source heat pump provides more detail on this topic.
An air source heat pump is typically located adjacent to the external wall of a house, where pipes can connect straight through the wall.
Our heat pump is located down the side of our house up against the wall.
For aesthetic reasons, a heat pump may instead be placed away from a home and surrounded by an enclosure, so long as airflow isn’t compromised. See our article on air source heat pump enclosures for more information.
Air source heat pumps require a flat surface for installation. If the ground around your building is sloped, you may need to build a flat surface for it to sit on. A concrete slab can be the most popular option.
Our ASHP sits on a concrete slab, which is covered with stones. There are mounting points across the base when the heat pump is bolted down to the slab.
There are also vibration mounts that we discuss in more detail below.
Rather than generating energy through combustion, an air source heat pump uses the energy and heat already available in the air to provide heat for a building.
To do this effectively, heat pumps must have sufficient airflow. If airflow is compromised, a heat pump can work at reduced effectiveness and be less energy efficient.
Sufficient airflow means that heat pumps should have a clearance distance on all sides to nearby objects in line with the manufacturers guidelines so that it has enough room around it to pull in and expel air.
Enough space is provided on all sides of our heat pump in line with the manufacturer’s specifications, and most importantly out the back of the unit between heat pump and the house where air is pulled in.
Similarly, they should be installed away from large bushes or other objects that can affect airflow.
High winds can also be counterproductive, and the manufacturer may specify what to do in locations that experience high winds.
It’s typically recommended that heat pumps are kept out of direct sunlight as much as possible as it can affect their operation and potentially decreases the unit’s efficiency.
Our manufacturer recommends to:
‘Avoid locations where the unit exposed to direct sunlight or other sources of heat.’
Whether you’re making a service call or working on the unit yourself, you must ensure that it’s located in an area that’s easily accessible.
Air source heat pumps will ideally be located away from nearby objects anyway for airflow purposes, but an installer will ensure adequate clearance is provided around a heat pump at installation to take into account accessibility for future maintenance and servicing.
See our article on air source heat pump space requirements for more information.
An air source heat pump will make a certain level of noise during operation.
This is due to the one or more fans running that is required to force air through the heat pump to capture heat.
An air source heat pump won’t typically need to run all the time but increases in demand or lower outdoor air temperature can lead a heat pump needing to run more often.
When choosing a location for an air source heat pump the noise emitted should be considered. Locations away from windows and from neighboring properties should be taken into account.
For example, our manufacturer explains to ‘select a location where noise emitted by the unit does not disturb neighbors’.
To help lower vibration, and therefore noise, our heat pump is installed on vibration mounts.
Refer to our article on air source heat pump noise for more information.
Temperature, snow, and rain are all essential considerations when deciding whether an air source heat pump is suitable for you and which type of heat pump to choose.
They are also important for choosing a location and coverage for a unit. Ensuring you meet the requirements for air source heat pump installation before you begin the process will save you time, money, and energy.
There are limits to the temperatures that an air source heat pump can tolerate as it becomes more difficult to extract heat out of the air when temperatures get too cold.
Air source heat pumps can stop working as effectively below 5°F (-15°C) but some may be able to operate at lower temperatures.
For example, our heat pump is guaranteed to work down to –4°F (-20°C) but not any lower than this.
As we live is a milder climate (the UK) temperatures won’t typically ever reach this low and so we can be assured that our heat pump will work no matter the time of year.
However, those who live in a climate where temperatures can reach below what an ASHP can work within may have problems using a typical air source heat pump.
Cold Climate Heat Pumps or CCHPs are designed explicitly for freezing climates, using different electronics and refrigerants to adapt. While they cost a bit more than the typical air source heat pump, they can be necessary for cold climates where a hybrid heating system won’t be used, such as with a backup boiler or furnace.
If you do not want a CCHP, there are a few options to make your air source heat pump function better in low temperatures, such as:
- Antifreeze: Antifreeze is a secondary refrigerant that can be added to your refrigerant to help it withstand colder temperatures. Adding antifreeze is a complicated procedure and should be done by a professional technician.
- Defrost Option: Some air source heat pumps have an automatic defrost setting, which kicks in when too much moisture begins to freeze on the unit. Unfortunately, there is a temporary break in heating when this cycle is running. The heat pump also uses additional energy to run the defrost.
- Split System: A monobloc system heats the air inside the outdoor unit before pumping it into the air ducts. When it’s cold outside, it becomes more difficult for the pump to heat the air outside. Split systems are better for cold climates because they collect the air outside but heat it in the indoor unit, which uses less energy.
Considering your local climate, in particular maximum and minimum temperatures that can be experienced throughout the year, when selecting an air source heat pump can therefore be an important requirement for the installation of an air source heat pump
Similarly, if you live in a climate that receives a lot of snowfall, you may not be able to keep your air source heat pump on the ground or the roof. If snow piles up around a heat pump it can compromise airflow.
Your air source heat pump should be high enough that snow will not pile up against it. This could be possible by mounting an air source heat pump on a wall. Alternatively, you could build a platform or stand to keep your unit above the ground.
Manufacturers will typically state what to do in areas that may experience heavy snowfall. For example, our ASHP manual explains to:
There are two basic types of air source heat pumps arrangements: Monobloc and split systems. While both are good options, there are different requirements for each. To choose the best system for you, consider your available space, both indoor and outdoors, and ductwork.
A monobloc pump is a single unit located outside your home.
Split systems have two slightly smaller main components, with one located outside, and the other placed in the individual spaces that require heating.
The system that works best for you depends on the available space you have. The monobloc may be the best option if you have ample outdoor space. A split system, on the other hand, may save you outdoor space if you have limited room outdoors.
Split systems (like ours) have just the external heat pump located outside, which can help keep outdoor noise down. It also allows us to have a smaller outdoor unit and all our main indoor apparatus is located in one cupboard, where a hot water tank to provide domestic hot water is also found.
Mini split air source heat pump systems, where one external heat pump connects to one or more air handling units inside serving individual rooms or spaces, can also be considered.
For the type of heat pump system chosen the space and installation requirements must be understood for that particular system.
While the external heat pump unit of an overall ASHP must follow certain installation requirements to ensure that its adequately sized and able to deal with climate conditions, the internal heating apparatus can play just an important role in ensuring that an air source heat pump system works as efficiently as possible.
The type of internal apparatus required can depend on the type of heat pump.
Air source heat pumps can be either air to air or air to water systems.
While the external air source heat pump unit used can be the same between the two systems, the internal heating equipment will differ.
Houses warmed by heated air will require an air to air heat pump system. This can include homes that have a central air handling unit with a series of ducts to move air around a home.
However, radiators and underfloor heating use water from a central heating system to create warmth and so homes heated this way will need an air to water heat pump system.
See our main article comparing air to air and air to water heat pump systems for more information.
We have an air to water system where an external heat pump is connected to a water-based central heating system inside our home.
The right internal heating apparatus was therefore required alongside our heat pump to make the most out of it. This included modern and large surface area radiators and underfloor heating.
When installing an air source heat pump in an older home, if the existing heating setup isn’t sufficient for use with a heat pump then it may also need to be upgraded or replaced.
A control system will also typically be required so that the homeowner can manage any heating, cooling or hot water settings.
We can control both our heating and hot water settings from a central control panel located just outside the cupboard where all our internal heating and hot water equipment is installed.
Each room on the lower floor of our home has thermostats to control the underfloor heating individually, and each radiator upstairs has its own control valve.
Finally, the insulation within a home must be of a sufficient level, otherwise heat can escape as quickly as its released and indoor temperatures will struggle to rise.
Air to air heat pumps work similarly to air to water systems by extracting heat from outside air, but differ in the way they deliver heat.
An air to air system will provide space heating inside a home, where heated air is delivered across a home through ducts, or within individual rooms.
Air handling units are typically required with such setups to provide the heating. The route of pipes to one or more air handling units must therefore be considered as part of the installation of an air to air heat pump system.
When a central air handling unit is used, a series of ducts throughout a home will be required to circulate the heat. Such setups can be common with homes that have existing ductwork to help keep installation costs lower.
If your home doesn’t have air ducts, you may need to select a ductless mini split air source heat pump as ductwork can be expensive to install.
Air to air heat pumps can also be used for cooling and can work much like traditional air conditioning units; extracting heat from indoor air and blowing cooler, conditioned, air back into the room.
However, an air to air system doesn’t heat water and so will require you to have a separate hot water system.
When installing an air to air heat pump system the requirements for ducts and/or internal air handling units will need to be considered, as well as consideration of how domestic hot water will be provided using another system, if required.
Air to water heat pumps work with water-based internal heating apparatus such as radiators and underfloor heating to heat a home.
The external heat pump of an air to water system will be similar to that of an air to air system and will extract heat from outside air.
However, unlike air to air systems where warmth is delivered indoors through heated air, an air to water system delivers heat around a home through water as part of a central heating system.
This means a network of pipes around a home to each room. Heat extracted by an air source heat pump will be transferred to this central heating system at the exchange point before it circulates around a home to release heat.
Heat is released within an air to water heat pump system using equipment such as underfloor heating and/or radiators, with large surface area to maximize how efficiently the heat is released.
For example, our home uses underfloor heating on the lower floor and radiators on the upper floor.
When installing an air to water heat pump system, the use of a suitable internal central heating system will need to be considered.
All of our main internal heating apparatus is located in one cupboard for ease of access and to keep it hidden out of view.
Air to water heat pump systems can also be set up to provide domestic hot water. This requires the use of a suitable hot water tank to work alongside a heat pump and to store and deliver hot water across a home.
Our hot water tank sits inside the same cupboard as all the other heating apparatus. It has been set up to work alongside the heating part of the system so that heat is delivered for hot water instead of the central heating when required.
As heat pumps extract and deliver heat more slowly compared to other heating systems, these hot water tanks are often equipped with electrical immersions heaters to top up water temperature when demand is higher.
If an air to water heat pump is also going to be used to provide hot water, then a suitable hot water storage tank must also be installed.
Refer to our main articles on using air source heat pumps with radiators and using air source heat pumps with underfloor heating.
Electrical Power Requirements
Air source heat pumps are electrical appliances and therefore require a suitable electrical power supply in order to work.
An external ASHP unit will therefore need to ideally be located in close proximity to an electrical supply.
Our heat pump takes power from the adjacent internal garage where mains power comes into our home.
It also has an isolation switch for cutting power to the heat pump for maintenance purposes etc.
Air Source Heat Pump Installation Requirements
There are a lot of different aspects to consider when installing an air source heat pump. Each type of pump has additional installation requirements that must be met for a whole heat pump system to work as effectively as designed.
Here is a brief overview of the requirements of different types of air source heat pumps:
- Monobloc systems require a larger outdoor space and existing ductwork.
- Split systems require space indoors to install air handling units, radiators, underfloor heating and any other additional heating apparatus.
- Air to air systems require air handling units and will need a separate water heating system for a home.
- Air to water units require the use of indoor radiators and/or underfloor heating. A hot water tank is also required if the heat pump is to also be used for domestic hot water.
- An external heat pump unit will need to installed in a suitable location that takes into account surrounding clearance space, noise, airflow, local climate, electrical power supply, and proximity to the indoor heating equipment. A heat pump will also need to be installed on flat solid base such as concrete slab and may require vibration mounts.
- A control system to be able to manage the heating, cooling, or hot water provided by a heat pump.