Exhaust air heat pumps provide ventilation as well as space and water heating in an all-in-one energy efficient solution. They boost the heat that a mechanical ventilation heat recovery system (MVHR) extracts from warm, stale indoor air and transfers it to heating systems. This can include the radiators in your home as well as hot water cylinders for showers and baths.

These systems are a popular choice with new-build developers and self-builders as they can save a significant amount of money, especially over a traditional gas system. They are also a cost effective way to meet building regulations requirements for ventilation, energy efficiency and comfort.

They work by reusing the energy stored in your house’s ventilation system, the fan blows air out of wet rooms like bathrooms, kitchens and utility areas and through vents in the outside walls into the open outside air. This fresh air then passes over an evaporator where the refrigerant is heated by the warm, stale indoor air and evaporates into a gas. This gas is then pumped into a compressor where it is raised in pressure and temperature and then used to supply the house with heating.

The system is very energy efficient and can be combined with a solar thermal system to achieve even higher levels of efficiency. The system is also available as a ‘cooling only’ system which takes the heat from the building in summer and uses it to provide comfort cooling. In addition to this, the system can be run in a combined mode which allows you to use both the heating and cooling functions together, for example when it’s a hot day.

This type of heat pump is designed to be fitted in conjunction with the ventilation system during construction, which means it has a much lower installation cost than a traditional system. It is possible to retrofit these systems into existing homes, but they will require a series of ducts to be built around the building for the air to get to and from the heat pump. This can be more disruptive than a full replacement and may not be as cost effective.

These systems can be a very affordable solution if you’re constructing a new-build property, a self-build or with a developer and need to comply with Code for Sustainable Homes renewable energy and ventilation requirements as well as meeting local authority fuel poverty rules. They are also a great way to add value and salability to an existing property as they are very cost effective to run.

A wide range of exhaust air heat pump connection schemes have been investigated and their performance analysed using a dynamic model of the heating system. The results show that the optimum configuration for a system using an exhaust air heat pump is with a recirculation circuit and a low return temperature to ensure maximum energy efficiency. The study also shows that the heating output of a ventilation-based system is highly dependent on the building standards and control strategy employed.