| Gallons per hour (gal/h) | Cubic feet per hour (ft³/h) |
|---|---|
| 1 Gallon per hour | 0.160543653247 ft³/h |
| 2 Gallons per hour | 0.321087306494 ft³/h |
| 3 Gallons per hour | 0.481630959742 ft³/h |
| 4 Gallons per hour | 0.642174612989 ft³/h |
| 5 Gallons per hour | 0.802718266236 ft³/h |
| 10 Gallons per hour | 1.60543653247 ft³/h |
| 20 Gallons per hour | 3.21087306494 ft³/h |
| 25 Gallons per hour | 4.01359133118 ft³/h |
| 50 Gallons per hour | 8.02718266236 ft³/h |
| 100 Gallons per hour | 16.0543653247 ft³/h |
| Reference | Gallons per hour (gal/h) | Cubic feet per hour (ft³/h) |
|---|---|---|
| A domestic shower | 118.783 gal/h | 19.0699 ft³/h |
| A kitchen tap | 131.982 gal/h | 21.1888 ft³/h |
| A garden hose | 197.972 gal/h | 31.7832 ft³/h |
| The Amazon river | 1.65505 × 1011 gal/h | 2.65708 × 1010 ft³/h |
The gallon per hour is a unit of volumetric flow rate equal to one imperial gallon passing a point every hour. Its symbol is gal/h, often abbreviated GPH. One imperial gallon is 4.54609 litres, so this unit describes the slow, sustained flows that matter over the length of a working day rather than a minute.
Fuel consumption is its most durable use. A boat's diesel engine burns 1 to 5 gallons per hour at cruising speed, a generator 0.5 to 2, and an agricultural tractor 2 to 4. Because such engines run at steady load for hours, the hourly figure multiplied by the hours of running gives the fuel bill directly, which is why boat and plant operators still think in these terms.
Oil-fired heating uses the unit for burner nozzles. A domestic oil boiler is fitted with a nozzle rated in gallons per hour — 0.5, 0.65 or 0.85 for a house — and that rating, multiplied by the calorific value of the oil, gives the heat output. Changing the nozzle changes the output, so the nozzle size on the burner label is effectively the rating of the appliance.
Water treatment and dosing are described the same way. A softener's regeneration flow, a chlorinator's feed rate and a chemical dosing pump on a cooling system are all set in gallons per hour, chosen so that the treated water leaves the plant with the concentration the process requires over a whole shift.
Older domestic water fittings carried the unit too. A header tank's fill rate, a cistern's refill and a slow-running standpipe were measured in gallons per hour in British practice, and the same figure told a householder how long a tank would take to recover after a bath had emptied it.
For scale, one gallon per hour is about 4.5 litres per hour, and 220 gallons per hour is about a cubic metre per hour. A rate of one gallon per hour would fill a domestic bath in about eighty hours, which is a fair reminder that this unit measures processes, not deliveries.
One gallon per hour equals about 4.546 litres per hour, about 0.004546 cubic metres per hour, or about 1.201 US gallons per hour.
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.