What is the ASHRAE 62.2 ventilation requirement?

ASHRAE 62.2-2019 formula: Q = 0.01 x Afloor + 7.5 x (Nbr + 1), where Afloor is conditioned floor area in sq ft and Nbr is number of bedrooms. For a 2,000 sq ft, 3-bedroom home: (0.01 x 2,000) + (7.5 x 4) = 50 CFM total mechanical ventilation. Buildings with blower door test results may subtract an infiltration credit (Section 4.1.3).

Air Change Rate Calculator

Calculate air changes per hour (ACH) from airflow and room volume, convert blower door test results to natural infiltration, and find ASHRAE 62.2 ventilation requirements. Includes a searchable room ACH reference.

Calculation Direction

Airflow Rate

Airflow(CFM)

Room Dimensions

Length(ft)

Width(ft)

Ceiling Height(ft)

Volume: 1,440ft³

Understanding Air Change Rates

What Is ACH?

Air changes per hour (ACH) measures how many times the entire volume of air in a room is replaced in one hour. An ACH of 6 means the room's air volume is exchanged six times per hour. Higher ACH removes contaminants faster but increases energy costs because conditioned air is exhausted.

Blower Door Tests

A blower door test measures building airtightness by depressurizing the building to 50 Pascals and measuring the airflow (CFM50) needed to maintain that pressure. The LBL correlation converts CFM50 to natural infiltration ACH using an N-factor that accounts for building height, wind exposure, and climate.

ASHRAE 62.2 Ventilation

ASHRAE Standard 62.2-2019 sets minimum ventilation rates for residential buildings. The formula combines a floor-area component (0.01 CFM/sq ft) and an occupant component (7.5 CFM per person, where occupants = bedrooms + 1). Buildings with demonstrated natural infiltration from blower door testing can take a credit against the mechanical ventilation requirement.

Tightness vs. Ventilation

A tight building envelope is always desirable — it reduces energy waste and improves comfort. But tight buildings need mechanical ventilation to maintain indoor air quality. The principle is “build tight, ventilate right” — seal the envelope, then add controlled mechanical ventilation sized to ASHRAE 62.2 requirements.

Recommended Air Changes per Hour by Space Type

Space Type	Min ACH	Max ACH
Bedroom	5	6
Living Room	6	8
Bathroom	8	10
Residential Kitchen	12	15
Restaurant Kitchen	15	25
Laboratory	10	15
Server Room	15	20
Hospital Operating Room	20	25

Typical ranges from ASHRAE Handbooks of Fundamentals and HVAC Applications. Local codes and specific conditions may require different rates. Use the Reference tab above for a searchable full-table view.

Frequently Asked Questions

How do I calculate air changes per hour (ACH)?

ACH = (CFM × 60) / Volume. Multiply airflow in cubic feet per minute (CFM) by 60 to convert to cubic feet per hour, then divide by room volume in cubic feet. For example, 200 CFM in a 1,440 ft³ room (15 × 12 × 8 ft) gives (200 × 60) / 1,440 = 8.33 ACH.

How do I calculate CFM from a target ACH (ACH to CFM)?

Rearrange the formula: CFM = (ACH × Volume) / 60. Multiply your target air changes per hour by room volume in cubic feet, then divide by 60. For 6 ACH in a 1,440 ft³ room: (6 × 1,440) / 60 = 144 CFM. This is the minimum supply airflow needed to achieve the target ventilation rate.

What does ACH50 mean compared to natural ACH?

ACH50 is the air changes per hour measured at 50 Pascals of depressurization — a standardized blower door test condition, not a normal operating condition. Natural ACH is the actual infiltration rate at ambient conditions. The LBL correlation estimates natural ACH as CFM50 / (N × Volume), or approximately ACH50 / N-factor. For most U.S. climates, natural ACH ≈ ACH50 / 17 to ACH50 / 22.

What is a good ACH50 for a house?

Below 3 is very tight (passive house level); 3–5 is tight (modern energy-efficient construction); 5–10 is average (typical existing homes); 10–20 is leaky (older construction needing air sealing); above 20 is very leaky. ENERGY STAR Certified Homes Version 3.2 requires ACH50 of 5–7 depending on climate zone.

How do I convert CFM50 to natural ACH from a blower door test?

Use the LBL (Lawrence Berkeley National Laboratory) N-factor correlation: Natural ACH = CFM50 / (N × Volume). N ranges from 12 to 22 depending on building height, wind exposure, and climate severity. A 1-story home in a cold climate with normal exposure uses N = 16.7. More sheltered or warmer climates use higher N-factors (less natural infiltration per CFM50 reading).

What is the ASHRAE 62.2 minimum ventilation requirement?

ASHRAE 62.2-2019 formula: Q = 0.01 × A_floor + 7.5 × (N_br + 1), where A_floor is conditioned floor area in ft² and N_bris number of bedrooms. For a 2,000 ft², 3-bedroom home: (0.01 × 2,000) + (7.5 × 4) = 50 CFM total mechanical ventilation. Buildings with blower door test results may subtract an infiltration credit (Section 4.1.3).

What are the recommended air changes per hour by room type?

Requirements vary significantly by space type: bedrooms 5–6 ACH, living rooms 6–8 ACH, residential kitchens 12–15 ACH, bathrooms 8–10 ACH, laboratories 10–15 ACH, server rooms 15–20 ACH, and hospital operating rooms 20–25 ACH. These are typical ranges from the ASHRAE Handbook of HVAC Applications. Local codes and ASHRAE 62.1 (commercial) may require different rates for specific occupancy types.

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