Specification errors risk costly redesigns
18 June 2026
Heat pumps are a key part of the government’s low-carbon agenda, but poor system design and product selection can lead to costly reworks. Dean Loizou, design director at Whitecode Consulting, explains common specification mistakes and compares system types, highlighting their respective advantages and drawbacks.
Despite heat pumps gaining importance in building design, specification and installation knowledge remains fairly limited. Consequently, there are some common installation mistakes that can have critical consequences for future rework and repairs.
Heat pumps can often be incorrectly sized. While undersized systems can lead to the systems cutting out and not providing any heat or reduced outputs, oversized heat pumps risk increased wear, significant inefficiencies, high operating costs and poor performance.
Conversely, a properly-sized heat pump will reduce the strain on the compressor and extend its lifespan while operating efficiently. Accurate sizing that accounts for room-by-room heat loss calculations will ensure the property remains cool in summer and warm in winter.
Sometimes, units are placed where airflow is restricted, such as in tight corners or near dense shrubs. This causes low efficiency and poor airflow. They can also be placed too close to other buildings; while they’re fairly quiet, they can cause a noise disturbance if installed near adjacent building windows or reflective walls.
Heat pump flow temperatures can often be set too high to ensure smaller, older radiators emit effective heating levels. However, the higher the temperature, the harder the heat pump has to work – meaning reduced efficiency.
What heat pumps are available and where should they be fitted? There are four types of heat pumps; air source, exhaust air, ground source and water source.
Air source
By gathering heat from the air and transferring it to a fluid refrigerant before it’s passed through a compressor, air source heat pumps (ASHPs) raise the fluid’s temperature before transferring heat to the building’s central heating system.
As ASHPs require efficient airflow, they must not be installed in enclosed spaces with insufficient ventilation, such as basements. Furthermore, avoiding any risk of noise pollution means they must be installed away from windows of neighbouring buildings.
They also produce more heat energy than electricity consumed, leading to lower overall operating costs over time.
Office energy managers and owners of commercial buildings in England and Wales can secure £7,500 in funding towards the average £11,000 installation cost via the government’s Boiler Upgrade Scheme (BUS).
Exhaust air
Exhaust air heat pumps (EAHPs) are ducted to the building façade and each room within a building. They utilise heat from outside to cool or heat 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 electrical and water connections required to the building, EAHPs remove the need for additional communal heating plant rooms.
There are multiple EAHP types, providing heating and cooling via a wet-based system – such as radiators, underfloor heating or fan coil units – utilising an integral MVHR system to provide heating and cooling, or providing hot water only.
Offering substantial Part F ventilation and Part O cooling capabilities, EAHPs don’t require the additional venting needed for more conventional MVHR systems.
More suited to domestic than commercial buildings, EAHPs can deal with smaller heating demands for low-energy properties.
EAHPs are also eligible for the BUS, with installation costs typically between £3,000 and £9,000.
Ground source
Separated into horizontal and vertical systems, ground source heat pumps (GSHPs) collect heat from the ground and transfer that into energy.
No matter the system, 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 compressed to raise its temperature. Subsequent heat is transferred into the central heating system.
Using consistent, stable ground temperature, GSHPs operate at 300% to 400% efficiency, offering more effective heating and lower running costs than conventional systems.
As horizontal trenches require large amounts of land, they can be unsuitable for smaller properties. The Environment Agency may also need to be consulted.
They require placement in basements or plant rooms and may need additional space for buffer tanks and hot water cylinders.
Funding towards the typical £29,000 installation cost can be received via an application to the BUS.
Water source
Available as closed loop and open loop systems, water source heat pumps (WSHPs) extract energy from water and turn it into heat.
To avoid freezing systems, they must be correctly sized and have appropriate water flow.
Fairly large in size and producing a low-level humming noise, WSHPs require installation in utility spaces, plant rooms or basements, and must be situated away from adjacent buildings.
Funding via the BUS can be sought to help cover some of the average £6,000 to £11,000 installation costs.
With reducing energy consumption and expenditure through the maximisation of heat pump efficiency a key aspect of building design, the importance of a holistic approach that involves specifiers, architects, developers and office energy managers at the earliest possible stage cannot be understated.
