Add multiple spaces when sizing a system that serves more than one room.
Room dimensions
Airflow — enter either value
CFM
cubic feet per minute
⇄
ACH
air changes per hour
Enter a CFM or ACH value above — the other will calculate automatically from your room volume.
Recommended range for this space
0—
—
CFM required
—
Air changes / hr
—
Total cu ft
System sizing details
Volume per change—
Time to fully exchange air—
Min. duct diameter (round)—
ASHRAE / code basis—
Equipment guide — by CFM range
Highlighted options are appropriate for your calculated CFM. Ratings shown are nominal — actual performance depends on static pressure and duct length.
Duct sizing reference
Based on 0.1" wg friction loss at 800 FPM velocity. Use next size up for runs longer than 25 ft or with more than two elbows.
ACH recommendations based on ASHRAE 62.1 / 62.2 and IRC mechanical code · CFM = (volume × ACH) ÷ 60 · Duct sizing at 800 FPM design velocity