Exhaust Air Heat Pumps – Considerations Before Specifying

Projects planning on using Exhaust Air Heat Pumps (EAHPs) should carefully review a number of technical and commercial factors prior to specification. Rushing to specify these systems without due consideration can result in unforeseen consequences for end-users, such as poor user experience, high costs, and uncomfortable summer temperatures.

EAHPs present an attractive solution for projects where a heat network is not suitable, and where individual conventional ASHPs cannot be accommodated. Units are entirely housed within the dwelling, with no external plant required, and by combining the delivery of heating, hot water, and ventilation in a single system it also removes the need for a separate MVHR or MEV system. EAHPs also deliver substantial CO₂ savings, assisting in the achievement of increasingly tough planning and Part L requirements that new projects face.

Nevertheless, careful consideration of the following factors should be taken:

• Cooling – not all EAHPs provide comfort cooling. Instead, some utilise enhanced ventilation rates and bypass functions to temper incoming air. The effect of this is limited in reducing overheating risk, and may not future-proof a scheme for a warming climate;
• Product support – EAHP manufacturers tend to be based outside the UK. Projects need to ensure there is a sufficient UK-based presence for timely post-installation support (e.g. maintenance activities), both within and out of the warranty period;
• User experience – Earlier iterations of EAHPs from 10-15 years ago were beset by instances of high running costs. Common causes included unnecessarily long periods where the back-up immersion systems were running, and high maintenance costs. Ensuring users understand how best to operate EAHPs can reduce this risk;
• Planning acceptability – whilst EAHPs may present attractive CO₂ savings, planning authorities which apply strict heat network policy zones may not grant planning permissions where they are proposed. Projects are encouraged to engage with planning authorities early to understand this risk.