Calculate the required CFM ventilation rate for a room or building. Determine airflow needs based on room size, occupancy, and ASHRAE standards.
CFM (cubic feet per minute) is the standard unit for measuring airflow in ventilation systems. The right amount of ventilation ensures healthy indoor air quality by diluting CO2, moisture, VOCs, and other contaminants. Too little ventilation causes health and comfort problems; too much wastes energy.
ASHRAE Standard 62.2 specifies minimum ventilation rates for residential buildings based on floor area and number of bedrooms (as a proxy for occupancy). Commercial buildings follow ASHRAE 62.1 with rates based on occupancy and floor area per zone.
This calculator determines the required CFM for your space based on ASHRAE guidelines. It covers both residential (62.2) and general occupancy calculations, helping you size ventilation fans, ERVs, and fresh air systems.
Understanding this metric in precise terms allows energy managers to evaluate investment options, forecast savings, and build compelling business cases for efficiency upgrades and retrofits. Tracking this metric consistently enables energy professionals and facility managers to identify consumption trends and implement efficiency improvements before costs escalate unnecessarily.
Proper ventilation sizing prevents indoor air quality problems while avoiding oversized systems that waste energy. This calculator applies ASHRAE standards to give you the correct CFM target for your space. Having accurate metrics readily available streamlines utility bill analysis, budget forecasting, and investment planning for energy efficiency projects and renewable energy installations.
ASHRAE 62.2 Residential: CFM = 0.03 × Floor Area + 7.5 × (Bedrooms + 1) General: CFM = (ACH × Volume) / 60 Per Person: CFM = Occupants × CFM_per_person
Result: 90 CFM required (ASHRAE 62.2)
For a 2,000 sq ft home with 3 bedrooms: CFM = 0.03 × 2,000 + 7.5 × (3 + 1) = 60 + 30 = 90 CFM. This is the continuous mechanical ventilation rate needed for healthy indoor air.
The 2019 version of 62.2 requires 0.03 CFM per square foot of floor area plus 7.5 CFM per person (estimated as bedrooms + 1). This formula produces ventilation rates of 60–120 CFM for most homes—achievable with a single ERV or HRV unit.
Exhaust-only (bath fan on a timer): simple, low-cost, but no heat recovery. Supply-only (fan coil or ERV supply): positive pressure, filters incoming air. Balanced (ERV/HRV): best energy performance, recovers 60–80% of heating/cooling energy. For new construction in cold climates, balanced ventilation with an HRV is the standard recommendation.
More ventilation isn't always better. Oversized systems waste energy, can cause comfort issues (drafts), and in humid climates, bring in excess moisture. Size the system to ASHRAE minimums and use demand control (CO2 sensors) if needed for spaces with variable occupancy.
Per ASHRAE 62.2: CFM = 0.03 × floor area + 7.5 × (bedrooms + 1). A 2,000 sq ft, 3-bedroom home needs 90 CFM continuous ventilation. This is the minimum for healthy indoor air quality.
ASHRAE recommends 50 CFM for bathrooms up to 100 sq ft, and 1 CFM per square foot for larger bathrooms. For bathrooms also serving as ventilation for the whole house, the fan must meet the 62.2 requirement.
ASHRAE 62.1 covers commercial and institutional buildings. ASHRAE 62.2 covers residential buildings. Commercial rates are typically higher per square foot due to higher occupancy density and pollution sources.
In tight homes, large exhaust fans (range hoods over 200 CFM) can depressurize the house, causing backdrafting of combustion appliances. A dedicated makeup air system or opening a window provides replacement air. Building codes often require makeup air for hoods over 400 CFM.
No — the CFM requirement stays the same. An ERV recovers heat/moisture from exhaust air, reducing the energy penalty of ventilation by 60–80%. You still need the same CFM for air quality; you just spend less energy conditioning it.
Use a flow hood over registers or exhaust grilles to measure actual airflow. Alternatively, use an anemometer in the duct and multiply velocity by duct cross-section area. Duct leakage often reduces delivered CFM by 10–30% compared to fan rating.