📊 Required Rate
⚖ Component Split
Calculation Breakdown
Full Calculation Table
| Component | Rate | Quantity | Result |
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How to Use the Whole-House Ventilation Calculator
Enter the home's total conditioned floor area, which drives the area-based portion of the rate.
Enter the number of bedrooms, which ASHRAE 62.2 uses with one added as a stand-in for occupancy, and the average ceiling height for the air change rate.
Choose exhaust-only, supply-only or balanced ventilation to see the fan airflow and pressure effect for that approach.
Click Calculate Ventilation Rate to see the required continuous airflow, its split between area and occupancy, and the air changes per hour.
The ASHRAE 62.2 Whole-House Ventilation Formula
ASHRAE 62.2 sets one continuous ventilation rate for an entire house, separate from the local exhaust that bathroom fans and range hoods provide. The rate is Qtot = 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1) in CFM, or 0.15 L/s per m² plus 3.5 L/s per occupant in metric. The first term covers background contaminants from the building and its contents, and the second uses bedrooms plus one as a stand-in for the people who live there. A 180 m² home with 3 bedrooms needs about 88 CFM (42 L/s). The standard also lets you take a credit for measured infiltration, which the ASHRAE 62.2 compliance calculator handles.
Why Bedroom Count Stands In for Occupancy
Actual occupancy changes over a home's life, but a ventilation system is designed once. Bedrooms plus one gives a stable, checkable number that approximates typical occupancy without a guess about who will live there.
Tighter Homes Need This More, Not Less
A tight house cannot rely on leakage for fresh air. An NRC article on why houses need mechanical ventilation reports that a 1989 survey found more than 70 percent of Canadian houses would average less than 0.3 air changes per hour over the heating season, and that tight houses can develop high humidity, mould and condensation. The air changes per hour result shows what the mechanical rate gives you. Check the home's actual leakage with the infiltration calculator.
Comparing the Three Strategies
Exhaust-only ventilation is the simplest and cheapest, with one fan pulling air out while replacement air leaks in through whatever paths it finds, unfiltered and without heat recovery. Supply-only flips that around, bringing in filtered outdoor air and pushing indoor air out through the envelope. A U.S. Department of Energy Building America guide for multifamily buildings notes that exhaust-only ventilation at 62.2 rates depressurizes tight units and supply-only can pressurize them, and recommends balanced ventilation for most high-performance construction. Balanced ventilation through an HRV or ERV matches supply and exhaust and recovers some energy, generally at a higher equipment cost. The ventilation energy recovery calculator puts a dollar value on that recovery.
This Rate Is Continuous, Local Exhaust Is Separate
The whole-house rate runs all the time, while bathroom and kitchen exhaust handle moisture and cooking contaminants where they occur. Size those with the bathroom fan calculator and kitchen exhaust calculator, and check the whole system once those loads run with the balanced ventilation calculator.
Exhaust Fans and Combustion Appliances
A house that is depressurized by exhaust fans can draw combustion gases back down a flue from a furnace or water heater. If you choose an exhaust-only strategy and have atmospheric combustion appliances, check the supply of air to them with the combustion air calculator.
Frequently Asked Questions
The continuous rate is 0.03 CFM per square foot of floor area plus 7.5 CFM times the bedrooms plus one. In metric that is about 0.15 L/s per square metre plus 3.5 L/s times the bedrooms plus one. A 180 m² home with 3 bedrooms (about 1,940 ft²) needs about 88 CFM, or 42 L/s. Bedrooms plus one stands in for the number of occupants.
Exhaust-only ventilation uses a fan to remove indoor air and lets replacement air leak in, which is simple and inexpensive but depressurizes the house and does not filter or recover heat from the incoming air. Supply-only ventilation brings in filtered outdoor air and lets indoor air leak out, which pressurizes the house and has no heat recovery. Balanced ventilation, usually an HRV or ERV, supplies and exhausts matched airflows and can recover heating or cooling energy, at a higher equipment cost.
No. The whole-house rate is continuous, general ventilation, while bathroom fans and range hoods remove moisture and cooking contaminants where they are produced. ASHRAE 62.2 sets separate local exhaust requirements for kitchens and bathrooms. Some homes run a bathroom fan continuously as part of the whole-house strategy, but a code-compliant home generally needs both.
No. Part 9 of the National Building Code, in Section 9.32, sets its own mechanical ventilation requirements for houses and lists CSA F326 as one way to comply, so the code rate can differ from the ASHRAE 62.2 figure. Confirm what your province has adopted and which method your authority accepts.