From conventional boilers to furnaces, many central heating systems are placed indoors, such as in a boiler room, basement, or kitchen. But does that hold true for air source heat pumps?
Air source heat pumps with split-type systems should be installed both indoors and outdoors. The part containing the evaporator needs to be placed outdoors, while the component with the condenser must be placed in your home. Packaged heat pump systems must be installed outdoors.
Our external air source heat pump unit is installed on the outside of our home, adjacent to the garage around the side of the house.
This heat pump unit can’t be installed inside and must be installed outside in line with the manufacturer’s guidelines.
We explain in this article more about our air source heat pumps and its outdoors installation requirements, how air source heat pumps work, and what apparatus as part of an overall air source heat pump heating system must be installed indoors.
Can Air Source Heat Pumps Be Installed Indoors?
Main air source heat pumps units should be installed outside in order to work as designed, but there are many components within the overall heating and/or cooling system of an air source heat pump that will need to be installed indoors.
Our heat pump is an air to water unit, meaning that it’s connected to our central heating and domestic hot water and provides the required heat for both. There’s no movement of air involved as would be the case with an air to air source heat pump unit.
This heat pump us used for heating purposes only and must be installed outside in order to work a designed. It can’t be installed indoors.
Our air source heat pump (ASHP) is therefore installed down the side of our house, just off the wall and in the open air.
It was installed here because:
- The heat pump can be noisy when operating and so is away from bedrooms and windows.
- It’s out of view from the front and back of the house.
This installation location had to be in line with the manufactures guidelines for locating this unit outside, which are shown below.
Reasons why this heat pump unit can’t be installed indoors include:
- It’s designed to extract heat from lower temperature air.
- It blows extremely cold air through removing heat, which would be counterproductive.
- Needs a sufficient supply of fresh air.
See our articles on where to install an air source heat pump and air source heat pump installation requirements for more information.
While the main unit of an air source heat pump system typically needs to be installed outside, much of the other apparatus within the setup will need to be installed indoors.
The pipes from our heat pump unit located outside our home extend through into garage and travel to the utility room cupboard where all the other main heating apparatus is located.
It’s within this cupboard where the water heater/hot water tank is located and where the heat (extracted from the air source heat pump unit located outside) is transferred to heat our water for central heating and domestic hot water.
We have a combination of underfloor (radiant) heating and large radiators throughout our home to help release this heat efficiently. See our articles on using air source heat pumps with underfloor heating and using air source heat pumps with radiators for more information.
Air Source Heat Pump Indoor & Outdoor Installation (How They Work)
To understand what parts of an air source heat pump system needs to be installed indoors and which components needs to be installed outside, it’s important to understand how an air source heat pump unit works.
Air source heat pumps work much like refrigerators in reverse: they draw in heat from the outside air and deliver it to an indoor space. Their evaporators turn the external heat into gas, while their condensers generate indoor heat, which returns to a liquid state.
In addition to the main heat pump unit and hot water tank (or air handler) that you would find in a typical air source heat pump system, each ASHP system also typically comes with these main parts:
- Coils and fins, which help transfer heat and evaporate and condense the refrigerant.
- Pipes through which the refrigerant flows.
- Compressor, which increases the pressure and heat.
- Reversing valve, which allows you to use the heat pump for cooling during summer.
See our article on parts of an air source heat pump explained for more information.
The following is how these parts work together:
- The outdoor coil heats the liquid refrigerant inside the pipes. The fins speed up the heat transfer process.
- Once the liquid refrigerant in the coil absorbs the heat from the outdoor air, the refrigerant evaporates into a gas.
- The heated gas refrigerant moves through a compressor for increased pressure and resulting increased temperature.
- The indoor coil transfers heat from the refrigerant to cool air or water for heating or hot water.
- After the heated refrigerant is circulated throughout a home, it condenses or returns to a liquid state, returning to the outside heat pump and repeating the heat cycle.
The main air source heat pumps units must be located outside for the above process to work.
See our article on how an air source heat pump works for further information.
Types of Air Source Heat Pumps
Air to air source heat pumps typically feature a split-type design, which has indoor and outdoor coils and an indoor fan. The fan circulates the heated air through ducts and supplied into a home.
Some models come in packaged systems, consisting of coils and fans that need to be placed outdoors. Like split-type systems, they are installed on existing ductwork and transfer heated air through the ducts.
There are also air source heat pump units that do not use ductwork. These ductless systems are relatively easy to install as they can be placed through a three-inch hole in a wall or a window.
See our article comparing ductless or ducted air source heat pumps for more information.
Air to water heat pump systems (like ours) use an outdoor heat pump unit to extract heat from the outside air before transferring that heat via liquid/gas for use within central heating and/or domestic hot water systems.
For more information see our article comparing air to air and air to water heat pumps.
Installing An Air Source Heat Pump Outside
Most air to air source heat pumps require ductwork, while air to water heat pumps will require pipework, and all systems need proper insulation and technical know-how.
That’s why installing one of these units calls for professional help and is not a job for DIY enthusiasts.
Understanding where an air source heat pump needs to be located, and which parts need to be located inside or outside, will help you to know whether this type of heating system is ideal for your property and its heating needs.
To install a ducted air source heat pump, an HVAC professional can do the following:
- Understand the heating requirements of the property.
- Identify the unit’s heating capacity, heat distribution network, and controls.
- Find the ideal location on your property to install the outside heat pump unit.
- Drill a hole in the wall to connect the pipes between the unit’s indoor and outdoor apparatus.
- Mount the outdoor part of the heat pump to the side of your house. For larger systems, the installer has to prepare a concrete slab first, which will serve as the base for the unit.
- Run the wires and pipes for the unit and insulate them.
- Secure the pipes to the wall.
For ducted air source heat pumps, installers will have to connect the units to existing ductwork. For ductless systems, they will just secure the units to the mounting plates on the wall.
An installed heat pump should have its outdoor condenser unit placed at the side of your house and its control box, air handler, or any associated apparatus located inside.
Once it’s installed, your installer should explain how to use the controls so that you can make the most of your unit.
You might also want to call in a technician every year for regular maintenance and inspection.
Is Your Home Ideal For An Air Source Heat Pump?
Air source heat pumps are perfect for apartments and other residences with limited space. Unlike ground source heat pumps, they neither take up much space nor need any groundwork. Plus, they run on electricity, so they’re great for homes that aren’t connected to any main gas lines.
While these systems require little space, their outdoor components have to be installed somewhere with sufficient airflow. And because they operate with fans, you also have to factor in the low noise they generate.
If you decide to get an air source heat pump, make sure that your home is well-insulated. Since they perform optimally in spaces that can keep the heat in, proper insulation is key to making it energy-efficient.
Apart from insulation, air source heat pumps require larger heat exchangers or radiators. The heat they produce is around 95 to 113 °F (35 to 45 °C), which is lower than what traditional central heating systems generate.
As a result, they need bigger radiators to effectively distribute heat, but underfloor (radiant) heating can work very well with heat pumps because their surface area is large in design.
Can Air Source Heat Pumps Be Installed Indoors?
Cost-saving, efficient, eco-friendly, and renewable heat—it’s no wonder why many homeowners are preferring air source heat pumps over other central heating systems. Unlike traditional heaters, they transfer heat available within the air outside to indoor spaces.
That’s what makes an air source heat pump unique. Because it uses outside air to heat up or even cool down a home’s interior, it’s an excellent choice for year-round temperature control.
That also means that certain apparatus as part of an overall air source heat pump system will need to be installed outside.
While air source heat pump units themselves will need to be located outdoors, all other apparatus such as hot water cylinders/water heaters or air handlers can be installed indoors.
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