PassiHEAT FAQ: Everything You Need to Know About Zero-Energy Passive Ventilation with Heat Recovery

PassiHEAT is PassiHVAC's wall-mounted passive ventilation unit with integrated heat recovery. Here are the key questions answered.

What is PassiHEAT and how does it work?

PassiHEAT is a dual-channel, cross-flow heat exchanger built into a compact wall unit. It supplies fresh outdoor air and exhausts stale indoor air through separate channels simultaneously — so streams never mix. Warm outgoing air heats the incoming cold air across the exchanger surfaces. Everything is driven by natural wind pressure and thermal buoyancy. No fans, no electricity, no moving parts.

Does PassiHEAT use any electricity?

No. PassiHEAT is entirely passive with zero running costs. No fans, motors, or electronic controls. This makes it ideal for social housing, retrofit projects, and any development targeting low-energy or net-zero performance standards.

How much heat does it recover, and how does airflow compare to a window?

PassiHEAT pre-warms incoming air by up to approximately 6°C, reducing space-heating demand in winter. It also delivers airflow velocities up to five times greater than a similarly sized top-hung window — meaning better ventilation even in low-wind urban conditions.

How is it installed, and does it work in retrofit?

Installation requires removing one to two standard UK bricks to form a wall opening. The unit protrudes slightly on the external facade to direct winds into the interior space. It is then weather-sealed and ready to use — no ductwork, no roof terminals, no electrical connections. It works in both masonry and timber-frame construction, making it well-suited to occupied retrofit projects and social housing programmes.

Does PassiHEAT help prevent damp and mould?

Yes. Damp and mould are frequently caused by inadequate ventilation, not just poor insulation. PassiHEAT provides continuous background ventilation without relying on occupants opening windows — something many avoid in winter to cut heating bills. By maintaining air exchange automatically, it removes excess moisture before it condenses and causes mould.

Where should PassiHEAT be positioned, and how do I get a quote?

For best results, install PassiHEAT adjacent to a radiator. This allows the radiator to further warm the pre-heated incoming air, eliminating any cold draught sensation. To request a quote or specification support, visit passihvac.com/contact — we also offer building performance modelling, SAP calculations, Daylight & Sunlight assessment, LCA etc. for planning and Building Regulations submissions.