An air source heat pump can be an air to air or air to water system.
Both systems have distinct outdoor and indoor units and specific appearances of the outdoor and indoor air source heat pumps depend on the size, capacity, design, and other features.
An outdoor air source heat pump unit can look much like a larger external air conditioning unit and be square or rectangular in shape. They will have one or more internal fans and typically be white, grey or black in color, or a combination.
Our own air source heat pump is a relatively large double-fan unit with internal compressor and finished in light grey.
While this is an external heat pump unit, it can be accompanied by a range of internal heating apparatus to make up a whole air source heat pump heating, cooling and hot water system.
We discuss and explain below more about what our air source heat pump looks like from all angles, the main parts that can you expect to see around an external heat pump unit, and what indoor equipment works alongside our outdoor heat pump.
Outdoor Heat Pump Unit
The actual look and shape of an air source heat pump (ASHP) can vary between manufacturers and models, but most outdoor ASHP units can look like external HVAC compressor systems such as the outdoor unit of a typical domestic air conditioning system.
While air source heat pumps can be used for both heating and cooling with the right setup, our own air source heat pump isn’t used for cooling, and only for heating and domestic hot water.
We therefore have separate air conditioning units and one can be seen installed next to our air source heat pump for comparison.
The size of our air source heat pump is much larger compared to our air conditioning unit, but the air con unit is serving one room while the heat pump needs to serve the whole house. See our main article comparing air source heat pumps and air conditioning units for more information.
The size of an air source heat pump can be influenced by a number of factors such as the size of the house, floor area, and the internal heating arrangement and its capability.
For larger houses with greater demand for heating, cooling or hot water, a greater capacity ASHP will typically be required, and so can be taller, wider and deeper depending on the model and design.
A single-zone air source heat pump has only one outdoor unit. A multi-zone air source heat pump may have two or more outdoor units stacked alongside or one over the other.
We have a single air source heat pump unit serving our whole house and is located down the side of our home.
It’s a twin-fan unit and so quite tall. To the right side of the fans is the compartment where all the other electrical and mechanical apparatus is located inside.
The fans force air through the unit from the back to capture heat.
To the left side of our ASHP unit is the side air inlet.
The right side of our air source heat pump is the power cable into the unit.
Power into the side of the heat pump comes from the mains electrics in our home. Air source heat pumps only require an electrical supply in order to work.
See our article on air source heat pump electrical requirements for more information.
Our heat pump sits on the ground and is mounted to the floor on a concrete base with vibration reduction. It may also be possible to mount an air source heat pump on an external wall.
The rear of our air source heat pump is open and contains the array of coils, where the refrigerant flows through to captures heat energy from the air.
We have an air to water heat pump and so the outgoing and incoming pipes, carrying the refrigerant to and from the heat pump, are located behind the heat pump and connected up to the back of the unit.
For more information on what air source heat pumps look like, here’s a YouTube video on how Mitsubishi and Carrier air source heat pumps look like side by side:
Air to Water Heat Pumps
Air to water heat pumps (like ours) differ to air to air heat pumps in that they’re used to heat water, whether that’s for central heating and/or domestic hot water, rather than providing space heating through warm air.
Heat energy captured by an air to water heat pump is transferred inside through refrigerant located in pipes.
As shown previously, these pipes connect into the back of our outdoor air source heat pump unit and travel indoors.
These pipes head through our internal garage and into our utility room cupboard where all of our internal heating and hot water apparatus is located.
Inside our cupboard is the hot water tank (more about using air source heat pumps with hot water tanks here), and all of the associated pipes and other equipment that allows our air source heat pump to provide both heating and hot water to our home.
Air to Air Heat Pumps
All air source heat pumps heating a house through air to air circulation are classified into two types: ducted and ductless.
The ducted versions have two styles, and ductless systems have three ways of circulating hot air from the heat pump to a room, area, or the entire house.
A ducted system uses an indoor air handler unit. You can set up an air source heat pump with the conventional HVAC ductwork.
The ductless systems use indoor heads mounted on the ceiling, wall, or floor. The wall-mounted heads can look like the indoor units of split air conditioners that work independently, not connected to an HVAC system or air handler. Floor-mounted units can also work independently, without ductwork, a centralized air handler, or an HVAC unit. The ceiling-mounted heads are cassettes.
See our main article comparing ductless and ducted air source heat pumps for more information.
An air source heat pump indoor cassette looks squarish and sits flush with the ceiling. The indoor heads mounted along the floor are low on the wall and sit partly recessed. Wall-mounted units are substantially wide and protruded. A ducted system looks like an HVAC ductwork.
You can conceal new ductwork for an air source heat pump by installing the ducts above the ceilings or below the floors. However, ductless systems occupy some indoor space along the selected walls unless you can get a ceiling cassette for a flawlessly flush installation.
For more information see our article comparing air to air and air to water heat pumps.
Air source heat pump outdoor and indoor units aren’t necessarily larger or smaller than those of HVAC systems. The ductless setups in these distinct categories can be identical. Also, many outdoor air source heat pumps are of similar sizes and shapes as the typical outdoor HVAC units.
An air source heat pump may be smaller than older boilers but bigger than the contemporary ones that don’t use hot water cylinders or storage tanks. However, air to water heat pumps don’t always use the same radiators as old boilers, so a complete overhaul can often be necessary.
See our guide on whether you need a boiler with an air source heat pump for more information.
Furthermore, air source heat pumps can offer cooling during the summer. Hence, the same system serves the purposes of the air conditioner and furnace of an HVAC system. In effect, your indoor installation is smaller as you don’t need the separate cooling and heating units of an HVAC.
Still, you need an air handler for ducted installations or indoor heads for ductless setups to heat and cool different rooms and areas. Air source heat pumps don’t typically demand more space than HVAC units, and you might save a bit as it provides both heating and cooling. However, the ductless systems with wall-mounted indoor heads require some space in every room or area.
An air source heat pump can look much like your typical domestic external air conditioning unit with fan and outer body.
The difference between an HVAC system and an air source heat pump is the latter’s reverse valve mechanism and electric resistance for auxiliary heating. All other major components, such as compressor, condenser, coils, and refrigerant, are used in both.
Thus, you’re not looking at an installation that’s vastly different from a typical HVAC system. If you plan to use the existing ductwork for an air to air heat pump, you may not need an overhaul inside your home. The only difference can be is an air source heat pump taking almost the same space as an HVAC outdoor unit.
Air to air heat pump systems can use air handlers or air conditioning-like units to distribute heat, while an air to water heat pump system can use radiators and underfloor heating to deliver heat, Air to water heat pumps can also be used with a hot water tank if also providing domestic hot water.