Exhaust Air Heat Pumps in Part L 2026

Air‑to‑water Exhaust Air Heat Pumps (EAHPs) no longer meet compliance under the newly released Part L 2026 regulations, while air‑to‑air systems do. Published on 24^th March 2026, this update marks the next major revision to the Part L building regulations.

EAHPs provide low carbon heating and hot water with an additional benefit of some cooling making them a useful to address Part O requirements. Their performance to mitigate overheating is linked to both their ventilation rate and cooling capacity.

Ensuring EAHPs perform well requires considering both:

• Ductwork design as EAHPs rely on ductwork to move air.

Long or complex duct routes increases the static pressure which reduces airflow. This also leads to high pressure drops which all contribute to reduced heat recovery higher fan energy use.

• Positioning EAHPs against the façade.

Unlike heat networks, they work best when duct runs are short and direct, preserving airflow and minimising system resistance. This also supports Part O compliance, as achieving the required ventilation rates is more reliable when the system is not constrained by unnecessary duct length or pressure losses.

Initial testing using the SAP 10.3 software shows that air to water EAHPs like the Qvantum and NIBE units do not currently provide a reasonable route to compliance with Part L 2026, falling short of the CO₂ target by 15-30%, a margin too large to compensate elsewhere in the specification.

In contrast, early testing of air-to-air EAHPs like the Nilan Compact P indicates a compliant solution, improving upon the CO₂ target by roughly 10%.  Similar air‑to‑air products are expected to perform comparably, but until they are listed on the PCDB, we cannot verify their performance.

It is expected that manufactures (Qvantum & NIBE) will respond to the tightening of Part L by improving their product efficiencies. EAHP performance will need to increase to remain a viable option, and while it is not yet clear how manufacturers will achieve this, further optimisation of existing technologies and test performance data is likely.

Additionally, the forthcoming Home Energy Model (HEM), which will replace SAP 10.3, adds further uncertainty. EAHPs may perform better or worse under the new methodology, and compliance positions could shift once HEM is released.