How much propane does a whole house generator use?

A 22 kW Generac Guardian burns 9.57 litres an hour at half load and 14.77 at full load, per its own spec sheet. Smaller units use far less: a 10 kW unit is 3.66 litres an hour at half load. Half load is the realistic figure for backup duty, where the generator is carrying a fraction of what it could. At those rates a 500-gallon tank holding 1,514 usable litres runs a 22 kW unit for about 158 hours, or 6.6 days.

How long will a 500-gallon propane tank run a generator?

About 6.6 days on a 22 kW unit at half load, and about 4.3 days at full load. Superior Propane publishes a 500-gallon tank's LPG capacity as 1,514 litres, and 1,514 divided by 9.57 litres an hour is roughly 158 hours. The load question moves that answer by more than two days on the same tank and the same machine, which is why it is a control on the calculator rather than an assumption.

Why is a 500-gallon tank only 1,514 litres and not 1,893?

Because propane tanks are filled to 80 percent. Superior Propane puts it plainly: LPG tanks are filled to a maximum of 80 percent of their capacity to allow for the natural expansion of liquid propane that occurs with a change in temperature. A 500 US gallon tank is 1,893 litres of steel and 80 percent of that is 1,514, which is the figure Superior publishes. This calculator uses that published figure as-is and does not apply the 80 percent again, which would understate your runtime by a day and a half.

Is propane or natural gas cheaper to run a generator on?

Natural gas, by roughly four to one. The same 22 kW machine over 24 hours at half load burns about $43 to $46 of natural gas at Enbridge's Rate 1 marginal rate, against about $161 to $218 of propane at Ontario's $0.70 to $0.95 a litre. Propane's advantage is that it needs no gas main, which matters in rural parts of the GTA and beyond it where there is no Enbridge service to connect to.

Should I get a bigger tank or a smaller generator?

Look at load before tank size. Moving from full load to half load on the same 22 kW unit stretches a 500-gallon tank from 4.3 days to 6.6, which is a bigger gain than most tank upgrades and costs nothing. That means being honest about what actually has to run: leaving central air off the generator is the single biggest lever, since a 3-ton unit adds 5,000 running watts. Our sizing calculator works out what your real load is.

Can I run out of propane during a long outage?

Yes, and it is the main practical difference between propane and a natural gas main, which does not run out. A tank has a fixed number of litres in it and a delivery truck during a regional ice storm is exactly what you cannot count on. Plan the tank around the longest outage you actually expect rather than the average one, and top up before winter rather than during it.

Propane Consumption Calculator for Generators

How long does a tank of propane last?

Generator sizeOnly sizes with a published Generac propane consumption figure.How hard is it working?This swings the answer by days, not hours. Half load is normal backup duty.Tank sizeSuperior's published LPG Capacity. This is the size RenoHouse prices for a standby generator install at $2,500 to $3,500 bought, or $200 to $400 a year rented.Outage you want to coverhours72 is a three-day ice storm.Your propane price$/LOntario residential propane runs $0.70 to $0.95 a litre per Avenir Energy, but bulk delivery is contract-priced, so your own invoice is the real figure.

A full 500-gallon tank runs it for

6.6 days

158 hours of continuous running at half load, burning 9.57 litres an hour from Generac's published spec sheet. One fill covers the outage you asked about.

Consumption at half load (Generac spec sheet): 9.57 L/h
Usable propane in the tank (Superior Propane): 1,514 L
Propane burned over the outage: 689 L
Propane for that outage: $586
A full tank at your price: $1,287

The tank figure is Superior Propane's published capacity in litres, used exactly as published. It already has the 80 percent fill rule in it: a 500-gallon tank is 1,893 litres of steel and Superior publishes its capacity as 1,514, which is that 80 percent. Taking another fifth off here would tell you the tank runs dry a day and a half early.

The 80 percent rule, and the mistake it causes

A propane tank is never filled to the top. Superior Propane states the rule directly: LPG tanks are filled to a maximum of 80 percent of their capacity, to allow for the natural expansion of liquid propane as the temperature changes. So a 500 US gallon tank, which is 1,893 litres of steel, is published by Superior with an LPG capacity of 1,514 litres. That figure is the 80 percent.

The mistake worth avoiding is applying the rule twice. It is easy to read 500 gallons, convert to 1,893 litres, remember the 80 percent rule and arrive at 1,514, which is correct. It is equally easy to take Superior's already-adjusted 1,514 and knock another fifth off it, arriving at 1,211 and telling yourself the tank runs dry a day and a half before it does. This calculator uses the published litre figure exactly as published, and there is a test in the repository asserting that it does.

Load matters more than tank size

The same 22 kW generator on the same 500-gallon tank lasts 6.6 days at half load and 4.3 at full. That is a swing of more than two days from one decision, and it costs nothing to make: it is a question of what you actually put on the generator. Central air conditioning is the usual culprit, since a 3-ton unit adds 5,000 running watts on its own, and an electric dryer or an electric water heater are close behind.

Which is why the honest order of operations is load first, then generator size, then tank. Our sizing calculator works out the load from your appliances, and the running-cost calculator compares what the same machine costs on propane against natural gas, which is about four to one in gas's favour. If a gas main is available at your address, our natural gas versus propane comparison sets out the whole trade-off, and the gas line cost guide prices the connection.

Frequently asked questions

How much propane does a whole house generator use?: A 22 kW Generac Guardian burns 9.57 litres an hour at half load and 14.77 at full load, per its own spec sheet. Smaller units use far less: a 10 kW unit is 3.66 litres an hour at half load. Half load is the realistic figure for backup duty, where the generator is carrying a fraction of what it could. At those rates a 500-gallon tank holding 1,514 usable litres runs a 22 kW unit for about 158 hours, or 6.6 days.
How long will a 500-gallon propane tank run a generator?: About 6.6 days on a 22 kW unit at half load, and about 4.3 days at full load. Superior Propane publishes a 500-gallon tank's LPG capacity as 1,514 litres, and 1,514 divided by 9.57 litres an hour is roughly 158 hours. The load question moves that answer by more than two days on the same tank and the same machine, which is why it is a control on the calculator rather than an assumption.
Why is a 500-gallon tank only 1,514 litres and not 1,893?: Because propane tanks are filled to 80 percent. Superior Propane puts it plainly: LPG tanks are filled to a maximum of 80 percent of their capacity to allow for the natural expansion of liquid propane that occurs with a change in temperature. A 500 US gallon tank is 1,893 litres of steel and 80 percent of that is 1,514, which is the figure Superior publishes. This calculator uses that published figure as-is and does not apply the 80 percent again, which would understate your runtime by a day and a half.
Is propane or natural gas cheaper to run a generator on?: Natural gas, by roughly four to one. The same 22 kW machine over 24 hours at half load burns about $43 to $46 of natural gas at Enbridge's Rate 1 marginal rate, against about $161 to $218 of propane at Ontario's $0.70 to $0.95 a litre. Propane's advantage is that it needs no gas main, which matters in rural parts of the GTA and beyond it where there is no Enbridge service to connect to.
Should I get a bigger tank or a smaller generator?: Look at load before tank size. Moving from full load to half load on the same 22 kW unit stretches a 500-gallon tank from 4.3 days to 6.6, which is a bigger gain than most tank upgrades and costs nothing. That means being honest about what actually has to run: leaving central air off the generator is the single biggest lever, since a 3-ton unit adds 5,000 running watts. Our sizing calculator works out what your real load is.
Can I run out of propane during a long outage?: Yes, and it is the main practical difference between propane and a natural gas main, which does not run out. A tank has a fixed number of litres in it and a delivery truck during a regional ice storm is exactly what you cannot count on. Plan the tank around the longest outage you actually expect rather than the average one, and top up before winter rather than during it.

Where these figures come from

Consumption rates from Generac's own published spec sheets, read in metric and column-matched to each model on the sheet itself. Tank capacities in litres from Superior Propane, Canada's largest propane supplier, used exactly as published. The propane price is yours to enter, because bulk delivery in Ontario is priced by contract and no government or utility source publishes a residential rate; Home Generator Index defaults it to a named Ontario supplier's published band and says so.