Exhaust air heat pumps recycle energy from the indoor air for heating, hot water and ventilation. This type of heat pump suits you if you want to reduce your energy costs, have no gas supply or just prefer a simple system that uses natural gases.

These systems are often more affordable than traditional heating, especially if your property is very well-insulated. They are also a good choice for new builds and renovation projects. However, if you choose to retrofit an exhaust air heat pump it’s important that the system is compatible with your existing hot water cylinder and plumbing arrangements. Our engineers can advise you on this, but it is best to search for FGAS or MCS certified installers to ensure you’re getting a high-quality system that’s installed correctly.

The main benefit of this type of heat pump is its ability to use the heat from your home’s ventilation system. This is because stale indoor air contains much more heat than fresh outdoor air, making it a valuable resource for the heat pump. It also makes sense from an environmental perspective to recycle energy that would otherwise be wasted in your house’s ventilation system.

The exhaust air heat pump’s fan extracts the stale indoor air and sends it outside. The warm air is then used to heat your hot water and the rest of the house. In this way, you can save up to 50% on your heating costs compared with a system using fossil fuels.

Several studies have examined the energy performance of exhaust air heat pumps and advanced ventilation heat recovery systems. The systems in question are designed to save energy in three different ways: by reducing the condensation temperature of the heat pump, by supplying fresh outdoor air and by reducing the ventilation load of the building. The energy efficiency of the heat pump system can vary depending on the system configuration, the outdoor climate and the behaviour of the users.

Exhaust air heat pump benefits

There are two main types of exhaust air heat pumps: air-to-water and air-to-air. In an air-to-water setup, the heat is transferred to water by running a loop of glycol or water around the heat pump or across a conductive plate that has heated exhaust air on one side and cool fresh air on the other. These systems can be 35 to 40 percent efficient, depending on the system configuration and the outdoor climate.

Air-to-air systems transfer the heat to fresh outdoor air, ideally by introducing it into the dwelling through various air intake grilles. These systems can be as efficient as an OAHP in hot climates, but require a larger air volume to provide the required heat because they don’t preheat the indoor air. A study by Shirani et al investigated the performance of several different air-to-air heat pump systems, and their variations in energy efficiency, and found that the performance is dependent on the temperature of the outdoor air, the size of the air intake, the butterfly valve opening degree, refrigerant concentration and the water flow rate.