The cubic foot per hour is a unit of volumetric flow rate equal to one cubic foot passing a point every hour. Its symbol is ft³/h, and in the gas trades it is abbreviated CFH. It is the unit of fuel gas supply throughout North America, where every appliance and every pipe is sized by it.
Natural gas is billed and metered in cubic feet, so the hourly rate is what a gas fitter works with. A domestic furnace consumes 80 to 150 cubic feet per hour, a water heater 40, a cooking range 65, and a whole house at design conditions perhaps 250. A residential meter is rated at 250 CFH and the service pipe at rather more.
Pipe sizing tables are built entirely around this unit. Given a length of pipe, a diameter and an allowable pressure drop, the table returns a capacity in cubic feet per hour, and the fitter compares it against the sum of the appliance ratings on that branch. Undersize the pipe and the burners starve when everything runs at once; oversize it and the material cost rises for no benefit.
The unit converts easily into heat. Natural gas carries roughly 1,000 British thermal units per cubic foot, so a rate in cubic feet per hour is very nearly the same number in thousands of British thermal units per hour. An appliance rated 100,000 British thermal units per hour therefore burns about 100 cubic feet per hour, which is why the two figures appear together on every rating plate.
Propane behaves differently and is worth stating separately. It carries about 2,500 British thermal units per cubic foot, so the same appliance needs less than half the volumetric flow, and a pipe sized for natural gas is generously large for propane. Confusing the two is a classic and dangerous error in the trade.
Beyond fuel gas, the unit describes slow air and gas flows in imperial practice: purge lines, instrument air, small blowers and laboratory gas supplies. Sixty cubic feet per hour is one cubic foot per minute, and 35.31 cubic feet per hour is one cubic metre per hour.
One cubic foot per hour equals about 0.02832 cubic metres per hour, about 28.32 litres per hour, or about 0.01667 cubic feet per minute.
| Unit | Symbol | 1 Cubic foot per hour equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Milliliter per second | mL/s | 7.86579071944 mL/s | 0.127132800206 ft³/h | Cubic feet per hour to Milliliters per second |
| Milliliter per minute | mL/min | 471.947443167 mL/min | 0.00211888000344 ft³/h | Cubic feet per hour to Milliliters per minute |
| Milliliter per hour | mL/h | 28316.84659 mL/h | 0.000035314666724 ft³/h | Cubic feet per hour to Milliliters per hour |
| Liter per second | L/s | 0.00786579071944 L/s | 127.132800206 ft³/h | Cubic feet per hour to Liters per second |
| Liter per minute | L/min | 0.471947443167 L/min | 2.11888000344 ft³/h | Cubic feet per hour to Liters per minute |
| Liter per hour | L/hour | 28.31684659 L/hour | 0.035314666724 ft³/h | Cubic feet per hour to Liters per hour |
| Cubic millimeter per second | mm³/s | 7865.79071944 mm³/s | 0.000127132800206 ft³/h | Cubic feet per hour to Cubic millimeters per second |
| Cubic millimeter per minute | mm³/min | 471947.443167 mm³/min | 0.00000211888000344 ft³/h | Cubic feet per hour to Cubic millimeters per minute |
| Cubic millimeter per hour | mm³/hour | 28316846.59 mm³/hour | 0.000000035314666724 ft³/h | Cubic feet per hour to Cubic millimeters per hour |
| Cubic centimeter per second | cm³/s | 7.86579071944 cm³/s | 0.127132800206 ft³/h | Cubic feet per hour to Cubic centimeters per second |
| Cubic centimeter per minute | cm³/min | 471.947443167 cm³/min | 0.00211888000344 ft³/h | Cubic feet per hour to Cubic centimeters per minute |
| Cubic centimeter per hour | cm³/h | 28316.84659 cm³/h | 0.000035314666724 ft³/h | Cubic feet per hour to Cubic centimeters per hour |
| Cubic meter per second | m³/s | 0.00000786579071944 m³/s | 127132.800206 ft³/h | Cubic feet per hour to Cubic meters per second |
| Cubic meter per minute | m³/min | 0.000471947443167 m³/min | 2118.88000344 ft³/h | Cubic feet per hour to Cubic meters per minute |
| Cubic meter per hour | m³/h | 0.02831684659 m³/h | 35.314666724 ft³/h | Cubic feet per hour to Cubic meters per hour |
| Cubic inch per second | in³/s | 0.479999999966 in³/s | 2.08333333348 ft³/h | Cubic feet per hour to Cubic inches per second |
| Cubic inch per minute | in³/min | 28.799999998 in³/min | 0.0347222222247 ft³/h | Cubic feet per hour to Cubic inches per minute |
| Cubic inch per hour | in³/h | 1727.99999988 in³/h | 0.000578703703745 ft³/h | Cubic feet per hour to Cubic inches per hour |
| Cubic foot per second | ft³/s | 0.000277777777778 ft³/s | 3600 ft³/h | Cubic feet per hour to Cubic feet per second |
| Cubic foot per minute | ft³/min | 0.0166666666667 ft³/min | 60 ft³/h | Cubic feet per hour to Cubic feet per minute |
| Fluid ounce per second | fl oz/s | 0.276837131493 fl oz/s | 3.61223219806 ft³/h | Cubic feet per hour to Fluid ounces per second |
| Fluid ounce per minute | fl oz/min | 16.6102278896 fl oz/min | 0.0602038699677 ft³/h | Cubic feet per hour to Fluid ounces per minute |
| Fluid ounce per hour | fl oz/h | 996.613673376 fl oz/h | 0.0010033978328 ft³/h | Cubic feet per hour to Fluid ounces per hour |
| Gallon per second | gal/s | 0.00173023207183 gal/s | 577.95715169 ft³/h | Cubic feet per hour to Gallons per second |
| Gallon per minute | gal/min | 0.10381392431 gal/min | 9.63261919483 ft³/h | Cubic feet per hour to Gallons per minute |
| Gallon per hour | gal/h | 6.2288354586 gal/h | 0.160543653247 ft³/h | Cubic feet per hour to Gallons per hour |
| US Gallon per second | gal US/s | 0.00207792207778 gal US/s | 481.250000034 ft³/h | Cubic feet per hour to US Gallons per second |
| US Gallon per minute | gal US/min | 0.124675324667 gal US/min | 8.0208333339 ft³/h | Cubic feet per hour to US Gallons per minute |
| US Gallon per hour | gal US/h | 7.48051947999 gal US/h | 0.133680555565 ft³/h | Cubic feet per hour to US Gallons per hour |