Propane tank for a generator

At half load, you can expect about 158 hours from a 22 kW generator using a 500 gallon propane tank, close to 6.6 days before a refill. That same generator can run about 79 hours on a 250 gallon tank.

158 h500 gal, 22 kW, half load

103 h500 gal, 22 kW, full load

79 h250 gal, 22 kW, half load

Tank life by size and load

Generac puts out a fuel table for every model. The models at 18 kW and 24 kW, plus those at 26 kW and at 38 kW, are rated so each burns no more fuel in an hour than the next size down. So the fuel burned per hour doesn't climb in step with kW.

Half load running time

Generator	Model	Propane an hour	120 gal	250 gal	500 gal	1,000 gal
10 kW	Guardian 10 kW	0.97 gal	99 h	206 h	412 h	825 h
14 kW	Guardian 14 kW	1.81 gal	53 h	110 h	221 h	442 h
18 kW	Guardian 18 kW	1.70 gal	56 h	118 h	235 h	471 h
22 kW	Guardian 22 kW	2.53 gal	38 h	79 h	158 h	316 h
24 kW	Guardian 24 kW	2.53 gal	38 h	79 h	158 h	316 h
26 kW	Guardian 26 kW	2.06 gal	47 h	97 h	194 h	388 h
32 kW	XG03245	3.40 gal	28 h	59 h	118 h	235 h
38 kW	RG03824	2.90 gal	33 h	69 h	138 h	276 h
48 kW	RG04845	4.20 gal	23 h	48 h	95 h	190 h

Full load running time

Generator	Model	Propane an hour	120 gal	250 gal	500 gal	1,000 gal
10 kW	Guardian 10 kW	1.48 gal	65 h	135 h	270 h	541 h
14 kW	Guardian 14 kW	3.07 gal	31 h	65 h	130 h	261 h
18 kW	Guardian 18 kW	3.02 gal	32 h	66 h	132 h	265 h
22 kW	Guardian 22 kW	3.90 gal	25 h	51 h	103 h	205 h
24 kW	Guardian 24 kW	3.90 gal	25 h	51 h	103 h	205 h
26 kW	Guardian 26 kW	3.63 gal	26 h	55 h	110 h	220 h
32 kW	XG03245	5.00 gal	19 h	40 h	80 h	160 h
38 kW	RG03824	5.20 gal	18 h	38 h	77 h	154 h
48 kW	RG04845	6.60 gal	15 h	30 h	61 h	121 h

Tanks have an 80% fill level. Each row uses Generac's fuel table for that model at half load and full load.

Propane tank runtime chart for a 22 kW generator by tank size — Running time by tank size for the 22 kW unit at each load.

Sizing a propane tank for generator use

A 22 kW unit can run for about 38 hours at half load with a 120 gallon tank, or 25 hours at full load. A 250 gallon tank gives you 2.1 to 3.3 days of operation. For a whole house generator, the usual 500 gallon choice provides 4.3 to 6.6 days. A 1,000 gallon tank works well for a house heated with propane and can also handle a long rural outage. Your propane supplier decides where the tank is placed. Most codes place it 10 ft from both the house and the generator.

Natural gas or propane

Piped natural gas requires no refills, although a disaster may cut the service. At the US average price, a 22 kW unit at half load uses natural gas for about $4.47 each hour. At the same load, propane costs about $6.91 per hour and provides 11% more power from the same unit. It also works where there's no gas main. Generator fuel consumption includes hourly figures for every size.