Cubic feet per minute. Systems are designed around cfm: about 400 per ton across a cooling coil, a set amount to each room's supply outlets, and minimum outdoor cfm for ventilation. Techs estimate it from external static pressure and fan tables, measure it with a flow hood at each outlet or a pitot traverse in the duct, or back it out of a temperature rise and known heat input.
Fan table says we're moving 950 cfm at 0.8 inches, on a 3 ton coil we should be up near 1,200.
Also heard as
- cubic feet per minute
Related terms
Static pressure
The pressure air exerts outward on duct walls, the resistance a fan works against, measured in inches of water column.
Ton
A unit of cooling capacity equal to 12,000 Btu per hour, the heat needed to melt a ton of ice in a day.
Test and balance
Measuring and adjusting a building's air and water flows so every outlet, coil and zone gets its design amount.
Diffuser
A supply air outlet, usually in the ceiling, that spreads air into the room in a set pattern and mixes it with room air.