Whole-House Ventilation CFM (ASHRAE 62.2)
Calculate the continuous fresh-air fan airflow a home needs under the ASHRAE 62.2 whole-house ventilation rate, from floor area and bedroom count.
Calculator
ASHRAE 62.2 whole-house ventilation for 2,000 sq ft with 3 bedrooms is about 90 CFM of continuous fresh air (0.03 × area + 7.5 × (bedrooms + 1)).
Modern homes are built tight to save energy, which is good for heating and cooling bills but bad for indoor air unless the house is ventilated on purpose. ASHRAE Standard 62.2 is the residential ventilation standard that sets a continuous whole-house mechanical ventilation rate so stale air, moisture, cooking byproducts and odors are diluted with outdoor air. This tool applies the core 62.2 formula to size that fresh-air fan in CFM (cubic feet per minute).
The rate scales with two proxies: floor area (a stand-in for the volume and off-gassing of the building) and bedroom count (a stand-in for the number of people). It is a whole-house rate — it does not replace local exhaust from bathroom and kitchen fans, which handle the spikes of moisture and grease at the source.
Formula
Qfan (CFM) = 0.03 × floor area (sq ft) + 7.5 × (bedrooms + 1)
The first term, 0.03 × area, covers the building itself; the second, 7.5 × (bedrooms + 1), covers the occupants (the “+1” assumes two people in the primary bedroom and one in each additional bedroom). The sum is the continuous airflow a whole-house fan should deliver.
Worked example
For a 2,000 sq ft home with 3 bedrooms:
0.03 × 2,000 = 60 CFM (building)7.5 × (3 + 1) = 7.5 × 4 = 30 CFM (occupants)60 + 30 = 90 CFM
So the whole-house ventilation target is 90 CFM of continuous fresh air. That could be met by a single quiet exhaust fan, a supply fan, a balanced HRV/ERV, or a central-fan-integrated supply running on a timer — 62.2 sets the rate, not the equipment. Convert that airflow into an air-change rate with the air changes per hour tool.
What the standard does and does not do
ASHRAE 62.2 defines the whole-house rate shown here plus separate local exhaust requirements: continuous or intermittent fans in bathrooms (typically 50 CFM intermittent / 20 CFM continuous) and a kitchen range hood (about 100 CFM intermittent vented outdoors). Some editions allow a credit for verified natural infiltration in leaky older homes, which can reduce the mechanical rate — a tight, new home gets little or no such credit.
Under-ventilating traps moisture and CO₂ indoors; grossly over-ventilating wastes the energy you spend heating and cooling that air. The 62.2 rate is the balance point. If you run a heat-recovery ventilator (HRV) or energy-recovery ventilator (ERV), you get the fresh air with much of the heat recovered. See the home ventilation guide for how the rate fits with your HVAC system.
How you deliver the rate should suit the climate. In a hot, humid region an exhaust-only fan pulls unconditioned outdoor air in through leaks, adding moisture; a supply or balanced system that filters and, with an ERV, partially tempers the incoming air is usually the better match. In a cold, dry climate an ERV instead conserves indoor moisture and heat. The 62.2 rate is the same either way — only the strategy changes. Whatever you install, verify the actual airflow with a flow hood or an anemometer once it is running, because a fan’s rated CFM and its installed CFM often differ by a wide margin after ducting and filters are added.
Reference table
ASHRAE 62.2 whole-house rate for common homes:
| Area (sq ft) | Bedrooms | Fan CFM |
|---|---|---|
| 1,200 | 2 | 59 CFM |
| 1,500 | 3 | 75 CFM |
| 2,000 | 3 | 90 CFM |
| 2,500 | 4 | 113 CFM |
| 3,000 | 4 | 128 CFM |
Whole-house rate only; local bathroom and kitchen exhaust are additional.