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Calculator · Ventilation
ASHRAE 62.2 ventilation calculator
Enter the conditioned floor area and bedroom count for a dwelling unit, and this calculator returns the whole-dwelling continuous mechanical ventilation rate from ANSI/ASHRAE Standard 62.2-2013 and every edition since. The formula, its two components and every constant are shown below.
- Type the dwelling unit's conditioned floor area in square feet, from 100 to 10,000.
- Count rooms used or intended for sleeping. A studio has 0 bedrooms.
- The result updates as you type and shows the floor-area and occupancy components separately.
Example result for the default inputs
Qtot = 0.03 x 2,000 sq ft + 7.5 x (3 + 1).
Required continuous ventilation
90 CFM
| Conditioned floor area | 2,000 sq ft |
|---|---|
| Bedrooms | 3 |
| Floor area component (0.03 x Afloor) | 60 CFM |
| Occupancy component (7.5 x (Nbr + 1)) | 30 CFM |
For estimation purposes only. Consult a licensed engineer for final designs.
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How the required ventilation rate is calculated
One equation covers every dwelling size and bedroom count with a floor-area term plus an occupancy term based on bedroom count. ASHRAE assumes one more occupant than bedrooms, so a one-bedroom unit is sized for two people. For most homes on this page, the floor-area term is the larger of the two. A small home with several bedrooms can flip that.
- Whole-dwelling ventilation rate
Qtot = 0.03 x Afloor + 7.5 x (Nbr + 1)Afloor is conditioned floor area in sq ft. Nbr is the bedroom count. ANSI/ASHRAE Standard 62.2-2013 (Addendum n to 62.2-2010) introduced this rate, and every edition since (62.2-2016, 62.2-2019, 62.2-2022) carries the same coefficients, Section 4.- Floor area component
0.03 x AfloorScales directly with conditioned floor area.- Occupancy component
7.5 x (Nbr + 1)A studio (Nbr = 0) still counts as one occupant, so this term never drops below 7.5 CFM.
Worked example across three house sizes
Run the formula on three houses. At 1,500 sq ft with 2 bedrooms it gives 67.5 CFM, and 2,000 sq ft with 3 bedrooms gives 90 CFM. The 3,000 sq ft, 4-bedroom house needs 127.5 CFM. Floor area doubles from the smallest house to the largest, and the requirement grows by less than that.
| House | Floor area term | Occupancy term | Qtot |
|---|---|---|---|
| 1,500 sq ft, 2 bedrooms | 45 CFM | 22.5 CFM | 67.5 CFM |
| 2,000 sq ft, 3 bedrooms | 60 CFM | 30 CFM | 90 CFM |
| 3,000 sq ft, 4 bedrooms | 90 CFM | 37.5 CFM | 127.5 CFM |
To check your own job, enter its floor area and bedroom count in the calculator at the top of this page. On a small unit with three or more bedrooms, look at the occupancy line first, since it can end up the larger term.
Standards and data sources
- ANSI/ASHRAE Standard 62.2, Ventilation and Acceptable Indoor Air Quality in Residential Buildings - sets Qtot, the whole-dwelling continuous mechanical ventilation rate this page calculates. The 0.03 and 7.5 coefficients date to the 62.2-2013 edition (Addendum n to 62.2-2010) and continue through the current 62.2-2022 edition.
- ASHRAE Handbook, Fundamentals - background on residential ventilation and indoor air quality that Standard 62.2 is built on.
- International Residential Code (IRC), Section M1505.4.3, Equation 15-1 - the 2018 and 2021 IRC's own whole-dwelling ventilation formula, 0.01 x CFA + 7.5 x (Nbr + 1), a lower CFM than the ASHRAE 62.2 rate above. Jurisdictions and efficiency programs that reference 62.2 use the higher rate. Check which formula the locally adopted code or program cites.
Limitations of this calculator
- This calculator skips the infiltration credit in Section 4, which lets a known blower-door air leakage rate reduce the required mechanical ventilation rate. The number above is the full rate before any credit, the conservative choice.
- It also skips the intermittent operation provisions. The CFM here assumes continuous operation. A fan cycling on a timer needs a higher CFM while it runs to move the same air over less time.
- Occupancy is set by bedroom count (Nbr + 1) alone, unrelated to how many people actually live in the house.
- This is a whole-dwelling code-minimum rate covering background ventilation for the unit as a whole. Bathroom and kitchen local exhaust are a separate requirement. See the bathroom exhaust fan calculator for that number.
- The 0.03 floor-area coefficient applies to ASHRAE 62.2-2013 and later. The IRC uses 0.01 (Section M1505.4.3).
- Whole-house Manual J and the formula calculators on this site are free. The BuildSolver chat runs a free whole-house Manual J. Room-by-room loads, Manual S equipment selection, Manual D and branded PDF export are on the Pro and Team plans.
Common ASHRAE 62.2 sizing mistakes
- Treating the whole-dwelling rate as a substitute for local exhaust. Qtot covers background ventilation for the whole unit. Bathrooms and kitchens still need their own local exhaust fans sized separately, regardless of whether the whole-dwelling system is running.
- Confusing the IRC formula with an outdated ASHRAE edition. The IRC's 0.01 x CFA + 7.5 x (Nbr + 1) (Section M1505.4.3) is a separate, currently active formula, distinct from ASHRAE 62.2. The 62.2-2010 edition used that same 0.01 coefficient before Addendum n raised it to 0.03 in 62.2-2013.
- Claiming an infiltration credit without the full calculation. The infiltration credit in Section 4 needs a blower-door CFM50 number, a weather and shielding factor and a stack-height correction together. An estimated leakage number plugged in without that full equation won't hold up with a plans examiner or a program rater.
- Running the continuous CFM on a timer-controlled fan without bumping it up. A fan cycling on a timer needs a higher CFM while it runs than the continuous rate above, since the standard's intermittent operation provisions call for more airflow per minute over a shorter run time.
- Submitting this number for a permit without checking the adopted edition. Some jurisdictions still adopt an older IRC or IECC edition, or a state energy code with its own ventilation table, so check the adopted edition on the state or local code adoption page (the DOE Building Energy Codes Program tracks state adoption).
Common questions about ASHRAE 62.2 ventilation
What CFM does a 2,000 sq ft, 3-bedroom house need under ASHRAE 62.2?
0.03 x 2,000 + 7.5 x (3 + 1) = 60 + 30 = 90 CFM of continuous whole-dwelling mechanical ventilation.
Does a studio apartment need mechanical ventilation under 62.2?
Yes. A studio counts as 0 bedrooms, so Nbr + 1 = 1 occupant-equivalent. For a 600 sq ft studio that works out to 0.03 x 600 + 7.5 x 1 = 18 + 7.5 = 25.5 CFM. Even a 100 sq ft accessory dwelling unit still needs 0.03 x 100 + 7.5 x 1 = 3 + 7.5 = 10.5 CFM, the bottom of this calculator's input range.
Which edition of ASHRAE 62.2 uses these coefficients?
62.2-2013 (Addendum n to 62.2-2010) introduced Qtot = 0.03 x Afloor + 7.5 x (Nbr + 1), and every edition since, 62.2-2016, 62.2-2019 and 62.2-2022, carries the same coefficients. The earlier 62.2-2010 edition used a smaller 0.01 floor-area coefficient with a default infiltration credit of about 2 CFM per 100 sq ft built into that rate, and 62.2-2013 moved infiltration to a separately calculated credit.
Why does the IRC give a lower number than this calculator?
The 2018 and 2021 IRC's own formula (Section M1505.4.3, Equation 15-1) is 0.01 x CFA + 7.5 x (Nbr + 1), using the smaller coefficient. A jurisdiction or efficiency program can adopt either the IRC formula or the ASHRAE 62.2 formula this page computes.
Can I subtract credit for a tight or leaky house?
The infiltration credit in Section 4 uses a measured blower-door CFM50 number, a weather and shielding factor and a stack-height correction together. This calculator does not compute that credit. The CFM above is the full rate before it.
Does this replace my bathroom exhaust fan requirement?
No. The whole-dwelling rate and bathroom or kitchen local exhaust are separate requirements. Use the bathroom exhaust fan calculator for that number.
What does a 10,000 sq ft, 8-bedroom house need?
0.03 x 10,000 + 7.5 x (8 + 1) = 300 + 67.5 = 367.5 CFM, the top of this calculator's input range.
Is this rate continuous or intermittent operation?
Continuous. Intermittent operation on a timer needs a higher CFM while the fan runs, using the standard's run-time correction, which this calculator does not compute.
Do single-family and multifamily units use the same formula?
The base Qtot equation is the same per dwelling unit. Attached and multifamily buildings can involve additional considerations, such as shared shafts or an attached-dwelling infiltration credit, outside this page's scope.
Used on the same job
- Bathroom exhaust fan calculator The bathroom-specific local exhaust number, separate from the whole-dwelling rate above.
- Manual J calculator Run the whole-house heating and cooling load while the ventilation numbers are on the table.
- HVAC CFM calculator Turn a design load into a design CFM for the whole system.
Run the whole-house load in chat
The chat has no ventilation tool, so the 62.2 rate comes from this page. Describe the house in chat and the assistant runs a free whole-house Manual J for it. Manual S equipment selection, room-by-room loads, Manual D duct sizing and branded PDF export are on the Pro and Team plans. Open the chat and start with the floor area and bedroom count you just entered.
Open the chat