15 April 2026
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Dean Loizou, Design Director at Whitecode Consulting, examines the different types of heat pumps and underscores each system’s advantages and disadvantages to enable the correct specification of them.
While the government’s 2050 net zero target is driving heat pump demand, there is some confusion in regard to the most suitable heat pumps, how, where and when they should be utilised in building design and what happens if they’re placed incorrectly.
Maximising the potential of heat pumps requires a true understanding and appreciation of the most suited system to the environment and a holistic approach between designer, developer, specifier and contractor.
There are four categories of heat pumps; air source, exhaust air, ground source and water source.
Air source
Air source heat pumps (ASHPs) gather heat from the air and transfer it to a fluid refrigerant. This is passed through a compressor – raising the fluid’s temperature before transferring the heat to the building’s central heating system.
There are two types of ASHP; monobloc and split. As a closed refrigeration cycle, monobloc systems transfer the heat to water and then either replace a boiler or be used on new low temperature district heating systems.
By continuing the refrigeration circuit into the building and using VRF pipework that’s distributed to internal units to provide heating and cooling, split systems are typically more efficient than monobloc systems.
With split systems separating the heat pump into indoor and outdoor units, some of the heat transfer occurs inside the building where it’s warmer – resulting in less heat being lost.
ASHPs typically produce more heat energy than the electricity they consume – leading to lower overall operating costs over time. They excel on sunny, south-facing walls. However, they must be installed away from bedrooms to reduce any risk of noise pollution and should not be located in enclosed spaces with insufficient ventilation, such as basements. Otherwise, this could lead to reduced outputs or the systems cutting out and not providing any heat.
ASHP installation cost varies depending on the building requirements and the size of the pump. But, on average, it’s approximately £11,000. The government’s Boiler Upgrade Scheme (BUS) helps offset the significant initial outlay, granting residents in England and Wales £7,500 in funding towards the overall cost.
Exhaust air
Exhaust air heat pumps (EAHPs) are ducted to the building façade and each room within the dwelling, utilising heat from inside and outside the dwelling to heat up or cool the space via the building’s ventilation system or a wet heating/cooling system.
With heating and cooling provided via the internal unit – and only a water and electrical connection required to the dwelling – EAHPs remove the need for additional communal heating plantrooms.
There are various types of EAHPs, with some utilising an integral MVHR system to provide heating and cooling to the space, some providing hot water only and others providing heating and cooling via a wet-based system, such as underfloor heating, fan coil units or radiators.
The ductwork used by the integral MVHR system to connect to the heat pump circuits not only provides ventilation but also, crucially, distributes heat to the space. The Part F ventilation and Part O cooling capabilities therefore remove the need for any additional venting requirements required for more conventional MVHR systems.
ASHPs are typically rated at 5kW, meaning they can often be too large for very low energy buildings. However, EAHPs are able to deal with smaller heating demands for very low energy buildings and Passivhaus properties.
EAHPs are eligible for the BUS, significantly helping to cover the £3,000 to £9,000 installation cost.
Ground source
Separated into horizontal and vertical systems, ground source heat pumps (GSHPs) collect heat from the ground and transfer that heat into energy for the building. Horizontal systems are laid in a shallow trench over a large surface area – ideal for large-scale developments with plenty of space. Utilising a borehole to ensure pipes are securely buried, vertical systems may prove more suitable for developers with little space to work with.
Regardless of the system chosen, pipe interiors feature a mixture of water and antifreeze, known as a thermal transfer fluid (TTF). This absorbs heat from the ground, which is passed through a heat exchanger into a refrigerant and then compressed to raise its temperature, with subsequent heat transferred into the central heating system.
Maintenance is often minimal and GSHPs typically last between 20 and 25 years. Leveraging the stable, consistent ground temperature, they provide more effective heating, operating at 300% to 400% efficiency and offering low running costs compared to more conventional systems.
However, installation can often cause significant disruption to the surrounding land and horizontal trenches require large amounts of land, making them unsuitable for smaller properties. And such, the Environmental Agency will need to be consulted.
GSHPs require placement in basements, garages or utility rooms and may need additional space for buffer tanks and hot water cylinders. This exacerbates the importance of correct specification and implementation during initial building design stages. With the typical cost of GSHP installation around £29,000, developers and specifiers can also apply to the BUS to receive £7,500 in funding towards it.
Water source
Water source heat pumps (WSHP) extract energy from the water and turn it into heat – no matter what the temperature of the water.
There are two main WSHP systems; closed loop and open loop. Closed loop systems are used in cooling towers, lochs, large ponds or lakes for heat rejection circuit. Sealed pipes are filled with an anti-freeze fluid and then submerged under the water. The fluid is pumped through the pipework, gathering heat energy from the water and then circulating back to the heat pump.
Open loop systems are used with boreholes near areas with suitable geological conditions or rivers. Water is taken from the borehole and lifted to the surface, extracting heat energy and then returning the cooled water to a separate borehole.
With a risk of the systems freezing as colder water leaves the heat pump, they must be correctly sized and there must be enough water flow to ensure freezing doesn’t occur.
Fairly large in size and producing a lowlevel humming noise, WSHPs will require installation in plant rooms, basements or utility spaces and be situated away from bedrooms.
WSHP installation costs typically range between £6,000 and £11,000, with developers and specifiers able to apply to the BUS to receive funding.
Correct specification is vital
While traditional fossil fuel boilers are often oversized to ensure demand is met, heat pumps require precise specification to match property heat loss. Otherwise, this risks high operating costs, poor performance, increased wear and significant inefficiencies.
A properly-sized heat pump will prevent frequent turning on and off – reducing the strain on the compressor and extending its lifespan while operating as efficiently as possible.
Accurate sizing that accounts for roomby-room heat loss calculations will also ensure the property remains warm in winter and cool in summer.
Heat pump location affects performance and occupant comfort, impacting noise levels, maintenance demands, longevity and overall system efficiency. While modern units are fairly quiet, they are still likely to cause a noise disturbance if installed near reflective walls or bedroom windows.
Furthermore, well-placed units – well away from corners or dense plants – will have access to unobstructed airflow and be ideally positioned for annual servicing, meaning they’ll be less likely to require expensive repairs.
Maximising heat pump efficiency and ultimately reducing energy consumption and expenditure for the building owner or end user will be crucial. The solution is a holistic approach that involves contractors, specifiers and architects at the earliest possible opportunity and has the most effective placement at heart.
