Air sealing and planned ventilation solve different problems: one limits uncontrolled leakage, while the other manages fresh air and pollutants.
1. Identify pollutants and moisture at their sources
List cooking, bathing, combustion, drying, cleaning and occupancy loads. Local exhaust is usually the direct response to a concentrated source; whole-house ventilation addresses the background requirement.
Do not use a single humidity or carbon-dioxide reading as a complete indoor-air-quality diagnosis. Sensors, locations and occupancy patterns all affect interpretation. Fuel-burning equipment requires combustion and carbon-monoxide safety checks.
DOE · Consumer guide to home ventilation ↗2. Define outdoor airflow before equipment
Determine the required outdoor-air rate from applicable local standards and the actual building. Record whether the system is supply-only, exhaust-only or balanced, and where air is intended to travel between rooms.
Measured fan airflow can differ from a label because ducts, filters and terminals add resistance. Provide commissioning points and access for cleaning rather than assuming installed flow equals catalogue flow.
3. Put ventilation into the heating calculation
Cold outdoor air creates a heating load proportional to airflow and temperature difference. The calculator uses a dry-air constant of 0.335 Wh per cubic metre-kelvin for a first estimate.
Heat-recovery equipment transfers sensible heat between exhaust and supply streams. DOE describes energy-recovery ventilation as controlled ventilation that reduces energy loss, but actual performance depends on airflow balance, frost control, leakage and operating conditions.
DOE Building Science · Energy recovery ventilation ↗4. Commission and maintain the air paths
Measure supply and exhaust flows, verify controls and check that local exhaust does not create unsafe pressure around combustion appliances. Document filter type, cleaning interval, condensate drainage and frost-mode behaviour.
Review the system after air-sealing work, equipment replacement or occupancy changes. A quiet fan is not proof of correct airflow, and a highly efficient heat exchanger cannot compensate for a blocked filter.
Keep four air quantities separate
| Quantity | How it is established | Common confusion |
|---|---|---|
| Planned outdoor air | Standard and design | Confused with fan label |
| Measured supply/exhaust | Commissioning | Assumed from control setting |
| Local extract | Kitchen and bath operation | Counted as continuous whole-house flow |
| Uncontrolled infiltration | Building leakage and weather | Treated as reliable ventilation |
Worked example
Heating 120 m³/h of outdoor air
Indoor air is 21°C, outdoor air is −10°C and sensible recovery is assumed to be 75%.
No recovery = 0.335 × 120 × 31 = 1.25 kW After recovery = 1.25 × (1 − 0.75) = 0.31 kW
This is a steady sensible-load estimate. Fan power, infiltration, humidity, defrost and part-load performance remain separate.
What to have ready
- Applicable outdoor-air requirement
- Measured supply and extract flows
- Indoor and outdoor design temperatures
- Recovery performance and frost-control data
Common mistakes
- Using uncontrolled leaks as a ventilation plan.
- Assuming labelled and installed airflow are identical.
- Ignoring filters, condensate and frost modes.
Reference check: 5 September 2026. Sources include US public agencies. Principles are general; regulations and design values must be checked where you live.Worked examples use stated hypothetical inputs.