| Space Type | Typical Target | Basis |
|---|---|---|
| Office | 4–6 ACH total supply | Rule of thumb. ASHRAE 62.1 OA ≈ 0.6 ACH* |
| Conference Room | 6–10 ACH total supply | Rule of thumb. ASHRAE 62.1 OA ≈ 2.1 ACH* |
| Classroom (age 9+) | 6–8 ACH total supply | Rule of thumb. ASHRAE 62.1 OA ≈ 3.1 ACH* |
| Corridor | 2–4 ACH total supply | Rule of thumb. ASHRAE 62.1 OA ≈ 0.4 ACH* |
| Exam Room (Medical) | 4–6 ACH total, 2 ACH OA | ASHRAE 170 (total depends on edition — check the adopted one) |
| Patient Room | 4–6 ACH total, 2 ACH OA | ASHRAE 170 (total depends on edition / supplemental heating-cooling) |
| Operating Room | 20 ACH total, 4 ACH OA | ASHRAE 170 |
| Laboratory | 6–10 ACH occupied | Lab design practice; fume-hood exhaust often governs |
| Commercial Kitchen | 15–60 ACH | Rule of thumb; hood exhaust governs. IMC Table 403.3.1.1 minimum exhaust 0.7 CFM/ft² |
| Restroom (public) | Exhaust 50 CFM per WC/urinal (70 intermittent) | IMC Table 403.3.1.1 |
| Parking Garage (enclosed) | Exhaust 0.75 CFM/ft² | IMC Table 403.3.1.1 |
| Warehouse | OA 10 CFM/person + 0.06 CFM/ft² | ASHRAE 62.1 (≈ 0.2 ACH at 20 ft) |
* ASHRAE 62.1 does not set ACH for these spaces. It sets outdoor air per person plus per square foot (Vbz = Rp·Pz + Ra·Az); the OA ACH shown is that rate at the Table 6-1 default occupant density and a 9 ft ceiling. Total-supply ACH for ordinary spaces is set by the cooling load, not by code.
Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.
Book a Demo →This air changes per hour calculator relates supply airflow, room volume, and ventilation rate. Choose what to solve for — ACH, CFM, or room volume — enter the other two values, and the tool returns the result plus the minutes required for one complete air change. A space-type selector shows a typical target and its basis alongside your number.
Engineers use ACH to size or check ventilation against codes that specify air changes rather than CFM, and to translate between the two. The reference targets show their basis — ASHRAE 170 for healthcare air changes, IMC exhaust rates, or a rule of thumb for total supply air — so you can tell a code minimum from a design habit. ASHRAE 62.1 sets outdoor air per person and per square foot, not air changes.
| Air changes/hr | ACH = (CFM × 60) ÷ Volume (ft³) |
| Required airflow | CFM = (ACH × Volume) ÷ 60 |
| Room volume | Volume = (CFM × 60) ÷ ACH |
| Minutes per change | min/change = 60 ÷ ACH |
The factor 60 converts CFM (cubic feet per minute) to cubic feet per hour so it can be divided by the room volume. Healthcare air changes follow ASHRAE 170 and exhaust rates follow IMC Table 403.3.1.1; restrooms, kitchens, and garages are specified as CFM per fixture or per square foot rather than ACH. Total-supply ACH ranges for offices, classrooms, and similar spaces are rules of thumb — ASHRAE 62.1 sets outdoor air per person and per square foot, not air changes. Confirm the governing rate against the code adopted in your jurisdiction.