HVAC CFM Calculator for Airflow Design
| Parameter | Value | Unit | Status | Notes |
|---|
- Manual J simplified: use 0.75 CFM/ftยฒ for standard residential homes.
- ACPH method is ideal for ventilation-critical spaces (kitchens, baths).
- BTUH method is the most accurate โ use post-load calc data when possible.
- Minimum supply air: 50 CFM per room per ASHRAE 62.2.
| Parameter | Calculated | Unit | Spec | Status | Notes |
|---|
- Flex duct: derate velocity by ~15% vs. rigid sheet metal.
- Target face velocity: 500โ750 FPM for supply, 400โ600 FPM for return.
- Rule of thumb: 400 CFM per ton โ 1-ton system needs ~400 CFM total.
| Parameter | Measured | Unit | Spec | Status | Notes |
|---|
400 CFM/ton is the residential baseline per ACCA Manual D.
ECM blowers maintain target CFM even as static pressure rises.
How to Calculate CFM Per Room and Per Square Foot
The HVAC CFM Calculator is designed for technicians and system designers who need to determine the required airflow for a space. Knowing the essential Cubic Feet per Minute (CFM) allows you to properly size a roomโs ductwork and ensure sufficient heating and cooling capacity.
Once you determine the room's CFM requirement, use our duct sizing calculator. By inputting the required CFM and a target friction rate (commonly 0.08 in. w.g./100 ft), the calculator outputs the recommended duct dimension.
Frequently Asked Questions
How much CFM do I need per ton?
The industry standard is 400 CFM per ton of cooling. In humid climates, this may be reduced to 350 CFM to improve dehumidification.
How do I calculate CFM per room?
The most accurate way is to divide the room's sensible heat load by the total system sensible heat load, then multiply by the total system CFM.