Generator Fuel Supply and Storage Guide

Fuel is the part of a standby generator plan that decides how long the home stays powered. Natural gas and propane behave differently at the supply level: one draws from a utility line with no tank to refill, the other draws from an on-site tank the owner has to monitor. The cited sources here separate the two supply models, the consumption figures that drive tank sizing, and the reason real outages rarely run at full load.

Two fuel supply models, two failure modes

Natural gas and propane are not just two prices for the same job. They are two different supply chains. Grounded Electric describes the natural gas model directly: the generator pulls from the home's existing gas lines, so there is no tank to refill, but the fuel source depends on utility service staying up. Propane is the mirror image. The same source notes propane needs an on-site tank the owner has to monitor and refill, but it keeps running even if the gas utility goes down.

That contrast is the real decision. A natural gas connection removes the refueling problem but ties the generator to the utility that may be affected by the same event causing the outage. A propane tank keeps the generator independent of the utility but reintroduces the refill and monitoring problem. M.T. Ruhl frames the upside of the utility line plainly: a Generac running on natural gas can operate indefinitely, for as long as the power is out, with no fuel delivery to schedule. The right answer depends on which failure mode the household can tolerate.

Natural gas consumption sets the meter draw

Natural gas consumption is measured in cubic feet per hour, and it climbs with load. Grounded Electric lists a 22 kW unit at about 203 cubic feet per hour at half load and about 306 cubic feet per hour at full load. Its natural gas per-hour breakdown gives a range view across sizes: a 20 kW unit at 180 to 250 cubic feet per hour half load and 250 to 290 at full load, and a 22 kW unit at 220 to 260 half load and 260 to 300 at full load.

Those figures matter because a natural gas meter and regulator have to deliver that flow. A unit that is correctly sized on electrical output can still starve if the gas supply cannot meet the cubic-feet-per-hour demand, which is why the consumption figure belongs in the install conversation and not just on a spec sheet. Grounded Electric also puts an operating cost on that draw: roughly $2 to $5 per hour on natural gas.

Propane consumption drives tank sizing

With propane, the consumption figure translates directly into how many days a tank lasts. Portlandia Electric Supply lists a 22 kW air-cooled unit at about 1.7 gallons per hour at 50 percent load and about 3.2 gallons per hour at full load, and a 26 kW unit at about 2.1 gallons per hour at 50 percent and about 3.9 at full load. Assurance Power Systems lists a comparable 22 kW figure of 2.1 gallons per hour at half load and 3.6 gallons per hour at full load.

Tank capacity turns those rates into runtime. M.T. Ruhl notes most residential standby generators connect to a 500 gallon propane tank filled to 80 percent, giving about 400 usable gallons. Grounded Electric puts a duration on that tank: at 3 to 4 gallons per hour, a 500 gallon tank may provide roughly 100 to 133 hours of continuous operation, or about 4 to 6 days. Portlandia's worked example scales down for a smaller tank, showing a 22 kW unit at half load using about 143 gallons over seven days at 12 hours per day, which a 250 gallon tank with 200 usable gallons covers with margin.

Plan around partial load, not the nameplate

The single most useful planning correction is that a home rarely runs its generator at full rated output. Portlandia Electric Supply notes most homes operate generators at 30 to 50 percent of capacity, which makes the half-load figure the appropriate planning baseline rather than the full-load number on the spec sheet. M.T. Ruhl shows the size of that gap in the field: a 22 kW unit rated to use about 3.5 gallons of propane per hour at full power was found using only around 1.2 gallons per hour during an actual outage.

That difference changes the tank math. Sizing a propane tank on the full-load rate overstates consumption and can push the owner toward a larger tank than the outage pattern requires, while sizing on the half-load rate reflects how the unit actually runs. The same logic caps the natural gas worry: the meter has to handle peak demand, but the fuel cost over an outage tracks the partial-load draw. Use the half-load figure to plan duration and cost, and reserve the full-load figure for confirming that the supply line or tank valve can meet peak demand.

What the fuel plan should show

A useful fuel plan makes both the supply model and the consumption math visible. It should state whether the unit runs on natural gas, drawing from the home's existing gas lines with no tank to refill but dependent on utility service, or on propane, drawing from an on-site tank that keeps running even if the utility goes down. Grounded Electric frames that as the core infrastructure difference, with natural gas suited to longer outages when utility service remains available.

The plan should also show the consumption figure at partial load, since Portlandia Electric Supply notes homes typically run at 30 to 50 percent of capacity. For propane, it should convert that rate into tank runtime, using the cited reference that a 500 gallon tank at 80 percent gives about 400 usable gallons and that 3 to 4 gallons per hour yields roughly 4 to 6 days. For natural gas, it should confirm the meter and regulator can deliver peak flow, since a 22 kW unit can draw about 306 cubic feet per hour at full load. That way the fuel plan connects the supply model, the consumption rate, and the duration the household actually needs.