Ventilation Sizing
Full Calculation Summary
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How to Use the ASHRAE 62.2 Calculator
Toggle imperial or metric units. Enter the total conditioned floor area of the dwelling unit across all levels, matching the area used for the building's energy code compliance.
The standard uses bedroom count plus one as an occupancy proxy — this is a fixed formula input, not an actual headcount, so a 3-bedroom home with 2 occupants still uses the 3-bedroom calculation.
If you have a verified ACH50 test result, select the matching band to apply the infiltration credit ASHRAE 62.2 permits. Leave on "Not Tested" if you don't have verified airtightness data, which is the conservative default.
Continuous operation is the standard design case. If intermittent operation is planned, select the schedule to see the required boosted instantaneous rate. Choose HRV or ERV based on your climate and moisture control needs.
Understanding ASHRAE 62.2 Residential Ventilation Requirements
ASHRAE 62.2 is the standard governing mechanical ventilation for low-rise residential buildings, establishing minimum continuous airflow rates intended to maintain acceptable indoor air quality as homes have become progressively more airtight. Understanding the formula and its components helps ensure HRV and ERV systems are sized correctly, neither under-ventilating occupants nor over-sizing equipment unnecessarily.
The two-part ventilation formula
The ASHRAE 62.2 formula combines a floor-area-driven component and an occupancy-driven component, reflecting two distinct sources of indoor air quality burden. The floor area component (0.03 cfm per square foot, or roughly 0.15 L/s per square metre) accounts for pollutants that emit continuously from building materials, furnishings, and finishes regardless of occupancy — off-gassing from paints, adhesives, and manufactured wood products. The occupant component (7.5 cfm per bedroom-plus-one, or roughly 3.5 L/s per occupant) accounts for pollutants generated by people themselves — carbon dioxide, moisture from breathing and activities, and various bioeffluents. Bedrooms-plus-one is used as a standardized occupancy proxy rather than requiring an actual headcount, which varies over time and is impractical to verify at design stage.
Why this is a continuous, not peak, ventilation rate
Unlike a bathroom exhaust fan or kitchen range hood, which operate intermittently to handle peak moisture or cooking pollutant loads, the ASHRAE 62.2 whole-house rate is designed to run continuously, 24 hours a day, to maintain a steady baseline of fresh air exchange. This is a fundamentally different design philosophy from spot ventilation: rather than reacting to peak events, continuous ventilation maintains consistent indoor air quality regardless of occupant activity patterns. Most residential HRV and ERV installations run at a low continuous speed most of the time, with an available boost mode for higher-demand periods like cooking or showering, layering intermittent spot ventilation on top of the continuous baseline.
The infiltration credit and its diminishing relevance
ASHRAE 62.2 permits a limited credit against the mechanical ventilation requirement for measured natural infiltration, recognizing that a leakier building already receives some fresh air exchange through unintentional leakage paths. However, this credit is capped and requires blower door verification — it cannot be assumed or estimated. Critically, as construction has tightened toward Energy Star and Net Zero airtightness targets (see the airtightness calculator for Canadian benchmarks), the available infiltration credit shrinks toward zero for buildings tested below roughly 3 ACH50. This means modern airtight Canadian construction typically must rely almost entirely on mechanical ventilation to meet the ASHRAE 62.2 requirement, making correct HRV or ERV sizing increasingly important as a primary (not supplementary) ventilation strategy.
Intermittent operation and the boost factor
While continuous operation is the standard's base design case, ASHRAE 62.2 permits intermittent operation using a specified multiplier to ensure the total daily air exchange remains equivalent. Running the system for 16 hours per day instead of 24 requires roughly 1.5 times the continuous rate during operating hours; running for 8 hours per day requires roughly 3 times the continuous rate. In practice, most residential designers favour continuous low-speed operation over complex intermittent scheduling, since it's simpler to commission, verify, and explain to occupants, and avoids the risk of a missed or malfunctioning schedule leaving the home under-ventilated for extended periods.
Cross-reference with the National Building Code of Canada
The National Building Code of Canada's residential ventilation provisions use a very similar floor-area-plus-bedroom methodology, producing results close to the ASHRAE 62.2 calculation for most typical Canadian dwelling configurations. Many Canadian jurisdictions reference ASHRAE 62.2 directly in their adopted energy code supplements, particularly for Net Zero and high-performance construction where the code explicitly calls out the ASHRAE standard. Use this calculator's result as a strong cross-check against NBC-derived ventilation requirements, and consult the NBC compliance checker for the specific Canadian code language applicable to your project.
Frequently Asked Questions
The ASHRAE 62.2 formula for continuous whole-dwelling mechanical ventilation combines a floor-area component and a bedroom component: required airflow equals 0.03 cfm per square foot of conditioned floor area, plus 7.5 cfm per bedroom-plus-one (using number of bedrooms plus one to approximate occupancy). In metric terms, this is approximately 0.15 L/s per square metre of floor area plus 3.5 L/s per occupant, using bedrooms plus one as the occupant estimate. This produces a continuous ventilation target intended to run at all times, not just intermittently. This calculator applies the formula directly to your dwelling's floor area and bedroom count.
ASHRAE 62.2 is a US standard, but its ventilation rate formula is closely mirrored in the National Building Code of Canada's residential ventilation provisions, which use a very similar floor-area-plus-bedroom calculation method. Many Canadian jurisdictions reference ASHRAE 62.2 directly or use NBC provisions derived from the same underlying research. This calculator applies the ASHRAE 62.2 formula, which gives results very close to the NBC method, useful both for direct ASHRAE compliance and as a cross-check against NBC ventilation requirements. Use the NBC compliance checker for the specific Canadian code language.
ASHRAE 62.2 allows a limited infiltration credit for homes above a certain airtightness threshold, reducing the mechanical ventilation requirement by accounting for some natural air leakage. However, the credit is capped and requires blower door test verification of the specific infiltration rate. As homes get tighter — particularly below roughly 3 ACH50 — this credit shrinks toward zero, meaning modern airtight construction typically must rely almost entirely on mechanical ventilation to meet the standard rather than counting on natural infiltration. Use the airtightness calculator to check your ACH50 result first.
ASHRAE 62.2 is fundamentally a continuous ventilation standard: the calculated rate represents the airflow that should run at all times to maintain acceptable indoor air quality. Intermittent operation is permitted under the standard's provisions, but requires a higher instantaneous airflow rate to deliver the same total daily air exchange in less running time, calculated using a specific intermittent operation factor. For most residential HRV and ERV installations, continuous low-speed operation with periodic boost is simpler to design, commission, and verify than a complex intermittent schedule. This calculator shows both continuous and intermittent operation rates.
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