Dew point: where water appears
The dew point is the temperature at which air, cooled at constant pressure and humidity, becomes saturated and water begins to condense. If a recovery core surface drops below the exhaust dew point, condensate forms on it – normal in cooling duty, a design input for drainage.
Frost point: where ice appears
Below 0 degC the same limit is the frost point: moisture deposits as ice instead of liquid. In cold-climate ventilation the exhaust airstream can sit below freezing while the supply is also cold, so the core can ice up and block airflow.
Why this bounds the design
Recovery only works while the core is open. Once frost bridges the channels, effectiveness collapses and fan power spikes. That is why climate-based selection matters: northern sites need defrost or frost-tolerant cores, not just a high nominal effectiveness.
Related reading
Protection strategies – purge sectors, preheat, bypass – are covered separately under frost protection in heat recovery systems.
Frequently asked questions
Is frost point always below dew point? For the same moisture content, yes – frost forms at a lower temperature than condensation because ice has lower vapour pressure than liquid water.
Do plates frost as badly as wheels? Plates can frost too, but a motorised bypass is simpler to apply than wheel regeneration.
Need help specifying the right air-to-air heat recovery for your project? Contact the QIYU engineering team – WhatsApp +86 157 5335 5505, or email kuns913@gmail.com.
Frequently Asked Questions
Why is dew point the critical temperature for a recuperator?
When the colder exhaust falls below the incoming air's dew point, moisture condenses on the core; below 0 degrees C it can frost and block the passages, so dew and frost point set the defrost or bypass strategy.
How do you protect a core in freezing climates?
Use frost-suppression methods such as preheating the supply air, recirculation or bypass of part of the exhaust, or wheel frost-control purging so the leaving-exhaust temperature stays above freezing.
Frequently Asked Questions
Why is dew point the critical temperature for a recuperator?
When the colder exhaust falls below the incoming air's dew point, moisture condenses on the core; below 0 degrees C it can frost and block the passages, so dew and frost point set the defrost or bypass strategy.
How do you protect a core in freezing climates?
Use frost-suppression methods such as preheating the supply air, recirculation or bypass of part of the exhaust, or wheel frost-control purging so the leaving-exhaust temperature stays above freezing.
Specify the right heat exchanger
Our engineers size the core to your airflow, temperature and pressure-drop budget, and select plate, rotary or heat-pipe recovery by application. Read the heat exchanger guide or contact us for a specification.
Related products
Plate, wheel or pipe recovery for HVAC and ventilation.
Stationary, high-surface-area cores for air and liquid.
High-effectiveness energy recovery for large airflows.
Passive, fully separated streams for clean applications.