Whole house · stack · 7 quick cards
ASHRAE 62.2, in Plain Numbers
8 cards · By the Air in the House editors, from ASHRAE, U.S. Department of Energy, International Residential Code, Home Ventilating Institute · how stacks are made · Updated
How much fresh air does a house need?
ASHRAE 62.2, the national home ventilation standard, sets a whole-house fresh-air rate of 0.03 cfm per square foot plus 7.5 cfm per person, counting bedrooms plus one.
- The ASHRAE 62.2 formula is 0.03 × floor area + 7.5 × (bedrooms + 1), in cfm of continuous airflow.
- Floor area stands in for pollutants from materials and furnishings; bedrooms + 1 stands in for the people (DOE Building America).
- Worked example: three bedrooms on 2,000 sq ft works out to 60 + 30 = 90 cfm under ASHRAE 62.2.
- The 2024 IRC table asks about 60 cfm for that same house, a lower code minimum.
- Local exhaust is separate: 50 cfm intermittent or 20 cfm continuous for a bathroom, 100 cfm intermittent for a kitchen.
- A ventilation designer or HVAC contractor sizes the real system; this stack only explains the arithmetic.
AI-made picture, not a photo of a real house What is ASHRAE 62.2?
ASHRAE 62.2 is the national standard, from the heating and air-conditioning engineers' society ASHRAE, that sets minimum ventilation for homes: a continuous whole-house rate plus kitchen and bath exhaust. It is a standard, not a law, and binds only where a code, program or contract points to it.
That is why two numbers float around for the same house. The International Residential Code carries its own ventilation table, and many towns build to that instead. The formula on this stack comes from the 62.2-2013 addendum approved in 2015 and is repeated in DOE's 2014 Building America profile; ask your designer which edition your project uses.
2024 IRC continuous ventilation, homes of 1,501–3,000 sq ft Bedrooms IRC table rate (continuous) 0–1 bedrooms 45 cfm 2–3 bedrooms 60 cfm 4–5 bedrooms 75 cfm 6–7 bedrooms 90 cfm More than 7 bedrooms 105 cfm How does the ASHRAE 62.2 formula work?
The ASHRAE 62.2 formula adds an allowance for the building to an allowance for the people who live in it:
Total ventilation (cfm) = 0.03 × floor area (sq ft) + 7.5 × (number of bedrooms + 1)
Turn over for the detail
The first term gives 0.03 cfm per square foot, because a bigger house holds more materials and furnishings that give off pollutants. The second gives 7.5 cfm per person, taking bedrooms plus one as the head count; a studio still counts as one bedroom.
The answer is continuous airflow: a fan running all the time at that rate, before any credit for air leaking through the shell. The standard allows that infiltration credit only when a blower door test has measured how leaky the house is. Without one, the full formula number stands.
Source the documents listed on this stack's sources card
Next What does a worked example look like?↓What does a worked example look like?
A 2,000 sq ft house with 3 bedrooms needs 90 cfm of continuous ventilation under ASHRAE 62.2, before any infiltration credit. The arithmetic:
- Building part: 0.03 × 2,000 sq ft = 60 cfm.
- People part: 3 bedrooms + 1 = 4 people, and 7.5 × 4 = 30 cfm.
- Total: 60 + 30 = 90 cfm, running continuously.
Turn over for the detail
That 90 cfm is the ASHRAE 62.2 figure, not a code requirement, and not the answer for your home: a designer adjusts it for a blower-door result, part-time fan schedules and what the fan really delivers through its ducts. Use it to read a plan, not to buy equipment.
Source the documents listed on this stack's sources card
Next How is ASHRAE 62.2 different from the building code table?↓How is ASHRAE 62.2 different from the building code table?
The IRC table usually asks for less air: the same 2,000 sq ft, 3-bedroom house needs about 60 cfm under 2024 IRC Table M1505.4.3(1), against 90 cfm from the ASHRAE 62.2 formula. The table groups homes by floor-area band and bedroom count.
The code also has two adjustments. A balanced system with supply ducts to each bedroom and to a living, dining or kitchen area may run 30% below the table. And a fan may cycle on and off if it runs no less than a quarter of every four-hour period, sized up to compensate: a fan running 25% of the time needs a factor of 4, one running 50% a factor of 2 (IRC M1505.4.3).
Turn over for the detail
Which rule applies depends on where you build. The 2012–2018 IRC required whole-house ventilation once a blower door showed 5 ACH50 or less; the 2021 and 2024 editions tie it to the energy code's airtightness limits. Your building department has the final word on which edition your plans must meet.
What about bathrooms and kitchens?
Bathrooms and kitchens get their own exhaust on top of the whole-house rate. For a bathroom, the IRC and ASHRAE 62.2 agree on 50 cfm intermittent or 20 cfm continuous. HVI's rule is 1 cfm per square foot for baths up to 100 sq ft, but that 50 cfm code floor means buying at least 50 cfm, rated at 0.25 in. static pressure.
Local exhaust minimums, IRC and ASHRAE 62.2 Room Switched on (intermittent) Always on (continuous) Bathroom or toilet room 50 cfm (both) 20 cfm (both) Kitchen, IRC 100 cfm 25 cfm Kitchen, ASHRAE 62.2 100 cfm 5 air changes per hour of kitchen volume Turn over for the detail
The IRC requires the fan to meet its number at 0.25 in. water column, and DOE's Building America guide notes that a fan sold as 50 cfm at 0.1 in. typically moves only 23–31 cfm at 0.25 in., closer to what real ductwork imposes. The bathroom fan size page goes further.
For a kitchen, the switched-on minimum is 100 cfm in both the IRC and ASHRAE 62.2. Always-on kitchen exhaust is where they part ways: the IRC says 25 cfm, while ASHRAE 62.2 says 5 air changes per hour of the kitchen's volume. Sizing a cooking hood is a separate question, covered on the range hood CFM page.
Who should do the actual design?
A ventilation designer or an HVAC contractor should size the real system, because the formula is only the starting line. They decide whether a blower-door result earns an infiltration credit, how a part-time schedule changes the fan size, and which fan delivers the target airflow at your duct's actual static pressure.
They also handle details the formula ignores: the outdoor air intake location (the IRC wants it at least 10 ft from vents, chimneys, streets and parking), controls with a labeled manual override, and the climate question of exhaust, supply or balanced (the Home Ventilating Institute explains all three). In Climate Zones 6–8, the 2024 IRC requires heat or energy recovery; see ERV vs HRV.
Turn over for the detail
If the plan leans on exhaust fans and a furnace, water heater or fireplace draws its combustion air from the room (anything not sealed-combustion or power-vented), ask for a combustion safety test by a qualified pro, since tight, exhaust-heavy houses can backdraft such appliances. If you're unsure, call a licensed pro. The exhaust, supply or balanced page lists what a contractor's plan should show.
The formula and the example, in numbers
- 0.03 cfmper sq ft of floor area in the ASHRAE 62.2 formulaASHRAE 62.2-2013 addendum m
- 7.5 cfmper person, counted as bedrooms + 1ASHRAE 62.2-2013 addendum m
- 90 cfmASHRAE 62.2 rate, three bedrooms on 2,000 sq ftASHRAE formula, worked example
- 60 cfm2024 IRC table rate for the same homeICC 2024 IRC Table M1505.4.3(1)
- 23–31 cfmtypical real airflow at 0.25 in. for a fan labeled 50 cfm at 0.1 in.DOE Building America
Chart drawn by Air in the House from figures cited in this stack.
Quick cards
Short questions people ask next, one answer each.
Does a home have to meet ASHRAE 62.2 if the local code uses the IRC table?
The adopted code is what an inspector checks, so the IRC table governs there. Some energy programs, builders or contracts call for ASHRAE 62.2 instead; your building department and paperwork tell you which applies.
Why does the formula count bedrooms plus one?
It's an occupancy estimate. Counting people in every home isn't practical, so the standard uses bedrooms plus one as a stand-in for the household, as DOE's Building America profile explains.
Does a bigger house always need more fresh air under ASHRAE 62.2?
Yes, the floor-area term grows by 0.03 cfm for every added square foot, even with the same number of bedrooms. The people term only changes when bedrooms are added.
Can the ventilation fan run part-time instead of all day?
Under the IRC, yes, if it runs at least a quarter of each 4-hour period and its airflow is scaled up to match. A designer works out the equivalent for an ASHRAE 62.2 design.
Does the 90 cfm in the example include the bathroom fan?
Not automatically. The whole-house rate and local bath exhaust are separate requirements, though a continuously rated bath fan can be designed to carry part or all of the whole-house rate.
What is an infiltration credit?
It's a reduction in the required fan airflow for fresh air that already leaks in through the shell. ASHRAE 62.2 allows it only after a blower door test has measured that leakage.
Is more ventilation always better?
Not without limit. Every extra cfm of outdoor air must be heated, cooled or dried, so designers aim for the required rate.
Where these cards come from
Explained from the ASHRAE 62.2-2013 addendum m (2015), DOE's 2014 Building America profile of 62.2, DOE's Building America ventilation guide and the 2024 IRC chapter 15, read in October 2026. This stack shows one worked example only; it gives no design tool, no infiltration-credit math and no claim about changes in later editions of the standard.
- ASHRAE ASHRAE 62.2 formula
- U.S. Department of Energy DOE Building America
- International Residential Code 2024 IRC Table M1505.4.3(1)
- U.S. Department of Energy a fan sold as 50 cfm at 0.1 in. typically moves only 23–31 cfm at 0.25 in.
- Home Ventilating Institute exhaust, supply or balanced
Cards are written by the Air in the House editors from the documents above and dated when they were last checked. How stacks are made