Winter humidity depends on outdoor air, indoor moisture sources and ventilation. Heat recovery does not automatically control humidity.
What heating changes
Cold outdoor air heated without adding water vapour has lower relative humidity. Assess temperature together with humidity and ventilation mode rather than one display reading.
Sources and measurement
Consider occupants, cooking, showers, drying and construction moisture. Log several days in representative rooms, checking sensor placement and reliability.
Exchanger type
A sensible exchanger recovers heat; an enthalpy exchanger can also transfer some moisture. Actual performance depends on the product, operating point and outdoor conditions rather than the technology label alone.
Damp surfaces and operation
Condensation at a cold junction calls for surface-temperature and moisture-source checks. Reducing ventilation to raise humidity can undermine pollutant removal; investigate the full system.
Common mistakes
Do not promise constant humidity solely by replacing the exchanger. Check settings, balance, frost protection, filters and drainage before specifying humidification or dehumidification.
| Item | Parameter | Check / result |
|---|---|---|
| Air | Temperature and humidity | Log |
| System | Flow and balance | Measurement |
| Envelope | Cold surfaces | Junction review |
What this means for your project
Start with temperature and humidity logs and a ventilation check. Select equipment after identifying the cause, considering the building envelope.
Sources and scope of review
- DOE Building Science Education — Energy recovery ventilation
- PNNL / Building America — Moisture control for residential buildings
Related reading
- Dew Point: Why the Simplified Rule Is Often Misleading
- Moisture in Assemblies: Diffusion, Convection and Leaks
- Ventilation Rates: How Much Air Does a Home Need?