PassiHEAT: Zero-Energy Passive Ventilation with Integrated Heat Recovery
PassiHEAT is a wall-mounted, fully passive ventilation unit developed by PassiHVAC to address the long-standing trade-off between indoor air quality and ventilation heat loss in naturally ventilated buildings. The system provides a continuous supply of fresh outdoor air while exhausting stale indoor air without electricity, fans, motors, or electronic controls, thereby eliminating operational energy demand and reducing maintenance requirements.
By combining passive ventilation with sensible heat recovery, PassiHEAT enables improved indoor environmental quality while limiting the thermal penalties typically associated with window-based background ventilation.
Technical Principle of Operation
At the core of PassiHEAT is a dual-channel cross-flow heat exchanger that maintains strict separation between the supply and exhaust air streams. Warm, polluted indoor air transfers sensible heat to the incoming fresh air across the exchanger surfaces, allowing heat recovery that would otherwise be lost through single-sided natural ventilation.
This configuration:
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Prevents air short-circuiting and cross-contamination
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Enables continuous background ventilation
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Operates silently due to the absence of mechanical components
The fully passive design ensures high reliability across varying seasons and wind conditions, making the system suitable for both urban and exposed locations.
Increase effective airflow velocities by up to five times compared with a similarly sized top-hung window opening, improving ventilation efficiency under low wind conditions.
Performance characteristics
Experimental testing and controlled evaluation have demonstrated a number of characteristics which support improved thermal comfort, indoor air quality, and energy efficiency in naturally ventilated buildings.
Installation and integration
PassiHEAT is designed for rapid installation in both retrofit and new-build applications. Typical installation involves removing one to two standard UK bricks to form a precise wall opening, into which the compact, aluminium-cased unit is mounted flush with the external façade.
The system is compatible with a wide range of construction typologies, including masonry and timber-frame walls.
No requirement for ductwork, roof terminals, or electrical connections
Minimal disruption during installation
Discreet internal positioning, often adjacent to radiators, to optimise perceived comfort and heat recovery effectiveness
Applicability and use cases
Owing to its zero-energy operation, low intervention requirements, and acoustic neutrality, PassiHEAT is suitable for a wide range of applications.
Visualising PassiHEAT integration
Interactive visualisations and typology examples demonstrate how PassiHEAT units can be integrated into typical UK building forms, illustrating adaptability across common residential contexts.