Ventilation Calculator — Free Online Calculator
Whole-building ventilation CFM is the baseline outdoor air rate your home or commercial space needs for acceptable indoor air quality — separate from heating and cooling airflow. Enter floor area and bedrooms for ASHRAE 62.2 residential sizing, or switch to commercial mode for ASHRAE 62.1 people-and-area rates. This tool splits the result into area and occupancy components so you can size an ERV, HRV, or fresh-air duct run with confidence.
Enter building details
62.2 for homes and dwellings; 62.1 for offices, retail, and other commercial spaces.
Conditioned floor area of the building or zone.
ASHRAE 62.2 estimates occupants as bedrooms + 1 (e.g. 3 bedrooms → 4 people).
Design occupancy for the space — from 62.1 Table 6-1.
Default 17.5 for open office — check your space type.
Default 0.06 for office — from ASHRAE 62.1 Table 6-1.
Required ventilation CFM
Area component
60 CFM
People component
30 CFM
What this means
Typical small home — Falls in the common ASHRAE 62.2 range for a 1,500–2,500 sq ft home with 2–4 bedrooms — confirm with local mechanical code and balanced supply/exhaust design.
See the breakdown
Results are simplified whole-building rates. Local codes may add kitchen/bath exhaust, infiltration credit, or balanced-ventilation requirements — verify before specifying equipment.
Ventilation CFM at common building sizes
Residential rows use ASHRAE 62.2 (0.03 CFM/sq ft + 7.5 CFM per bedroom + 1). Commercial row uses a typical open-office rate from ASHRAE 62.1 (17.5 CFM/person + 0.06 CFM/sq ft).
| Building type | Floor area | Bedrooms / occupants | Area CFM | People CFM | Total CFM |
|---|---|---|---|---|---|
| Residential (62.2) | 1,500 sq ft | 2 bedrooms | 45 CFM | 23 CFM | 68 CFM |
| Residential (62.2) | 2,000 sq ft | 3 bedrooms | 60 CFM | 30 CFM | 90 CFM |
| Residential (62.2) | 2,500 sq ft | 4 bedrooms | 75 CFM | 38 CFM | 113 CFM |
| Commercial office (62.1) | 2,000 sq ft | 10 occupants | 120 CFM | 175 CFM | 295 CFM |
Sources & standards: ASHRAE Standard 62.2 (Ventilation and Acceptable Indoor Air Quality in Residential Buildings) · ASHRAE Standard 62.1 (Ventilation and Acceptable Indoor Air Quality).
The formula, explained in plain English
Whole-building ventilation CFM is the continuous outdoor air rate needed to dilute indoor contaminants — not the same as heating or cooling airflow. Residential and commercial standards use different formulas, but both split the rate into an area-based component and a people-based component.
62.2 is for homes
The residential whole-building rate scales with floor area and estimated occupancy (bedrooms + 1). Typical results are 60–120 CFM for single-family homes — much lower than cooling system airflow.
62.1 is for commercial
Commercial rates come from Table 6-1 by space type. Open offices often use ~17.5 CFM/person plus 0.06 CFM/sq ft — people ventilation usually dominates in occupied spaces.
Not the same as CFM/ton
A 3-ton AC moving 1,200 CFM is conditioned air through the coil. Ventilation CFM is fresh outdoor air for IAQ — sized with this calculator, not the CFM per ton rule of thumb.
Size ERV/HRV to this rate
Pick a balanced ventilation unit rated at or above the calculated CFM. Then size the dedicated ventilation duct with the duct calculator — typically smaller than main supply trunks.
Worked examples
Three common sizing scenarios — two residential homes per ASHRAE 62.2 and one commercial open office per ASHRAE 62.1.
2,000 sq ft home — 3 bedrooms (defaults)
people = 7.5 × (3 + 1) = 30 CFM
total = 60 + 30 = 90 CFM
Result: a typical mid-size home needs 90 CFM continuous ventilation — size a 90–100 CFM ERV/HRV and verify balanced supply/exhaust per local code.
2,500 sq ft home — 4 bedrooms
people = 7.5 × (4 + 1) = 37.5 CFM
total = 75 + 37.5 = 113 CFM
Result: larger floor area and an extra bedroom push ventilation to 113 CFM — common for 4-bedroom homes; confirm duct sizing for the longer fresh-air run.
2,000 sq ft open office — 10 occupants
people = 10 × 17.5 = 175 CFM
total = 120 + 175 = 295 CFM
Result: people ventilation dominates in an occupied office — 295 CFM total outdoor air. Verify space type in ASHRAE 62.1 Table 6-1 before specifying DOAS or AHU outdoor air.
Frequently asked questions
Common questions about ASHRAE 62.2, 62.1, ERV/HRV sizing, and ventilation vs. cooling CFM.
What is ASHRAE 62.2 and when do I use it?
ASHRAE Standard 62.2 is the residential ventilation and acceptable indoor air quality standard. Use it for single-family homes, townhouses, and similar dwellings. The whole-building rate combines a floor-area component (0.03 CFM per sq ft) plus an occupancy component (7.5 CFM per person, estimated as bedrooms + 1). This calculator applies that simplified whole-building formula — confirm local code adoption and any amendments.
What is ASHRAE 62.1 and how is it different from 62.2?
ASHRAE Standard 62.1 covers commercial and institutional buildings. Ventilation rates come from Table 6-1 by space type — typically a people rate (CFM per occupant) plus an area rate (CFM per sq ft). ASHRAE 62.2 is residential-only. Switch the calculator to commercial mode and enter occupancy and rates from your space category in 62.1.
How do I size an ERV or HRV from this CFM number?
The calculated CFM is your continuous whole-building ventilation target. Size the ERV or HRV to deliver at least that rate at balanced supply and exhaust. Most manufacturers list nominal CFM at a specific static pressure — pick a unit rated at or above your result and verify duct runs, filters, and defrost performance for your climate. Pair with the Duct Size Calculator for the ventilation trunk and branches.
What's the difference between this and the CFM calculator?
They answer different questions. The CFM Calculator sizes heating and cooling airflow — room air changes, CFM per ton, and equipment delivery. This ventilation calculator sizes outdoor air for indoor air quality per ASHRAE 62.2 or 62.1. A 3-ton system might move 1,200 CFM of conditioned air while the whole-building ventilation requirement is only 60–120 CFM of fresh outdoor air.
Does ASHRAE 62.2 include kitchen and bathroom exhaust?
The whole-building rate in 62.2 is the continuous baseline ventilation — it does not replace intermittent local exhaust for kitchens and bathrooms. Those are separate requirements (typically 25–100 CFM intermittent for kitchens, 50 CFM for bathrooms). An ERV/HRV handles the continuous portion; range hoods and bath fans handle peak moisture and contaminant loads.
What CFM does a typical 2,000 sq ft home need?
Using ASHRAE 62.2 defaults — 2,000 sq ft and 3 bedrooms — the whole-building rate is 90 CFM: 60 CFM from floor area (0.03 × 2,000) plus 30 CFM from occupancy (7.5 × 4 people). A 1,500 sq ft, 2-bedroom home is about 68 CFM; a 2,500 sq ft, 4-bedroom home is about 113 CFM.
Can I use this for a small office or retail space?
Yes — switch to commercial mode and enter occupancy plus people and area rates from ASHRAE 62.1 Table 6-1 for your space type. The default office example (10 people, 17.5 CFM/person, 0.06 CFM/sq ft on 2,000 sq ft) yields 295 CFM. Large or complex buildings still need engineering-grade load calculations; treat results here as a first-pass sizing check.
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