PassiHEAT: zero-energy passive ventilation with integrated heat recovery
PassiHEAT is a wall-mounted, fully passive ventilation unit developed by PassiHVAC Limited to address the long-standing trade-off between indoor air quality and ventilation heat loss in naturally ventilated buildings. The system delivers a continuous supply of fresh outdoor air while simultaneously exhausting stale indoor air, without electricity, fans, motors, or controls, thereby eliminating operational energy demand and associated maintenance burdens.
Technical principle
At the core of PassiHEAT is a dual-channel cross-flow heat exchanger that maintains strict separation between supply and exhaust air streams. Warm, polluted indoor air transfers sensible heat to the incoming fresh air through the exchanger surfaces, recovering heat that would otherwise be lost through window-based single-sided ventilation, while preventing air short-circuiting and cross-contamination. The absence of mechanical components ensures silent operation and high reliability across all seasons and wind conditions.
Performance characteristics
Experimental testing indicates that the system can:
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Increase effective airflow velocities to up to five times those achieved through a similarly sized top-hung window opening, enhancing ventilation robustness under variable external conditions.
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Pre-warm incoming air by up to ~6°C, materially improving winter thermal comfort and reducing space-heating demand associated with ventilation.
Installation and integration
PassiHEAT is designed for rapid retrofit and new-build integration. Installation typically involves removing one to two standard UK bricks, forming a precise wall opening into which the compact aluminium-cased unit is mounted flush with the façade. No ductwork, roof cowls, or electrical connections are required. Internally, the unit can be positioned discretely (often near radiators) to optimise perceived comfort and heat recovery effectiveness.
Applicability and use cases
Owing to its passive operation and minimal intervention, PassiHEAT is suitable for:
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Residential housing and social housing retrofits, where low cost, zero running energy, and ease of installation are critical.
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Schools, universities, and healthcare settings, where improved indoor air quality is required without acoustic disturbance.
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Commercial and light-industrial buildings, including heritage assets, where conventional mechanical ventilation or ducting is impractical.
Visualising PassiHEAT integration
Below, you can interactively explore how PassiHEAT devices can be integrated into a range of typical UK building typologies, illustrating their adaptability across common residential contexts.