Here's the short answer, since that's probably what you need: A Generac standby generator burns somewhere between 0.5 and 2.5 gallons of natural gas or propane per hour, depending on the load. A 22kW unit at half load is gonna use about 1.5 gallons of propane per hour. On natural gas, it's roughly 200-250 cubic feet per hour under the same conditions. The real question isn't just how much it burns—it's how you make sure you have enough when you need it.
When I took over purchasing for my company back in 2021, I spent about 6 months trying to figure out fuel consumption for our backup generators. We had a mix of Generac units across three facilities—in case you're wondering, that's for about 400 employees in total. I ordered fuel supply contracts, tracked usage logs, and even did a side-by-side test with a 12kW and a 24kW unit to see if the larger one was really that much thirstier. I'm not a mechanic or an engineer. I'm just the person who has to sign the purchase orders and explain the budget variance to finance.
The Numbers You Actually Need
Here's a rough guide based on what I've seen from our logs and from specs. Take the figures with a grain of salt—actual consumption depends on the ambient temperature, the specific load, and how well the unit is maintained.
Generac Fuel Consumption at 50% Load (Typical Usage)
I'm giving you the 50% load numbers because that's what most people actually run. A 22kW unit powering your essential circuits—fridge, furnace, some lights, internet—is probably pulling around 10-12kW of load. The max load is usually for a few minutes during startup, not sustained.
- 12kW unit: ~0.9 gallons of propane per hour (~125 cubic feet of natural gas)
- 22kW unit: ~1.5 gallons of propane per hour (~200 cubic feet of natural gas)
- 24kW unit: ~1.6 gallons of propane per hour (~215 cubic feet of natural gas)
- 36kW unit: ~2.4 gallons of propane per hour (~325 cubic feet of natural gas)
- 48kW unit: ~3.2 gallons of propane per hour (~425 cubic feet of natural gas)
These are not the marketing numbers. Marketing numbers are usually at 25% load, where efficiency looks better. I found that out the hard way.
The Thing Most Buyers Miss
Most buyers focus on the per-gallon or per-hour fuel cost and completely miss the logistics of fuel supply during an extended outage. I made this mistake myself. I remember in 2022, we had a 3-day outage from a winter storm, and our 22kW unit ran for about 55 hours. The fuel consumption was fine on paper—about 80 gallons of propane. The problem wasn't the consumption. It was the fact that our 120-gallon tank ran low on day two, and the propane delivery trucks couldn't get through the snow. We had to manually switch to a backup tank from a different vendor.
The question everyone asks is, "How much fuel per hour?" The question they should ask is, "How do I guarantee fuel delivery during an emergency?"
If you're on propane, your tank size matters more than the hourly consumption. A 500-gallon tank for a 22kW unit running at half load gives you about 13 days of continuous operation (500 gallons minus the 20% you can't use at the bottom). Sounds great until you realize the delivery trucks might not run for a week. For natural gas, the question is about the capacity of your gas line and whether your utility can sustain supply during a regional event.
Testing for Voltage with a Multimeter: A Quick Tip
Since we're talking about practical stuff, here's something I learned the hard way when we were testing fuel pump outputs on an older Generac. If you need to test for voltage with a multimeter, always set it to AC if you're testing the generator's output (the 240V line) and DC if you're testing control circuits or battery voltage. I once fried a meter because I switched them. Use the proper setting.
How to Test
- Turn the generator off and disconnect it from the load.
- Set your multimeter to AC voltage, range 600V or auto-ranging.
- Probe the output terminals (L1 and L2 for 240V, L1 to neutral for 120V).
- Start the generator and check the reading. A healthy unit produces within 5% of rated voltage.
- For the fuel pump, you'd use a DC voltage setting (12V or 24V) and probe the pump's supply wires.
Tool for Fuel Pump Removal
If you need to replace a fuel pump on a Generac, the specific tool for fuel pump removal is often a snap ring pliers set and a small pick tool. The pump is usually held in by a retaining ring, not a threaded connection. I watched a technician struggle for 20 minutes with a regular pliers before grabbing the right one. You can also use a radiator hose pick to disconnect the fuel lines without damaging them.
The Dual Function Circuit Breaker
This is another detail that trips people up. A dual function circuit breaker (which combines GFCI and AFCI protection) is commonly required in newer electrical codes for certain circuits in a home—like bedrooms and living areas. When you're installing a Generac transfer switch, you need to make sure the transfer switch's circuits are compatible with the breakers in your main panel. Some older transfer switches don't handle the neutral current of shared neutrals found in multi-wire branch circuits. Generac's newer switches are fine, but you should ask your installer to check.
Why You Should Buy from a Generac Generator Authorized Dealer
I've seen people try to save a few hundred dollars by buying from a non-authorized seller online. The result: they end up with a unit that's missing parts, has an incorrect warranty, or they can't find a local installer who will touch it. An authorized dealer doesn't just sell you the machine—they handle the installation, the fuel line connection, and any warranty claims that come up. When we had a controller board failure on a 2-year-old unit, the authorized dealer replaced it under warranty in three days. A non-authorized seller would have made me ship the entire unit back.
In our 2024 vendor consolidation project, we cut back on eight different suppliers for various office needs, but I intentionally kept two authorized Generac dealers on the list—one primary and one backup. That redundancy cost us a little in administrative overhead but saved us during the 2022 storm when our primary couldn't get to us.
Don't Forget the Specifics
I'll be straight with you: I'm not 100% sure about every single model's consumption numbers, because Generac updates their engines and controller firmware. The figures I gave above are for the air-cooled models (Guardian series) from 2020-2024. Liquid-cooled units (Protector series) tend to be a bit more efficient per kW, but they also cost more upfront. Always check the spec sheet for your specific model number.
And take any online fuel consumption calculator with a grain of salt. The best way to know is to run your unit under a realistic load for an hour and check your propane tank gauge or gas meter. That's what we did for our annual load bank test. The numbers I got off the meter were within 5% of the spec sheet, which was reassuring.
“An informed customer asks better questions and makes faster decisions.” — I'd rather spend 10 minutes explaining consumption rates than deal with a fuel shortage at 2 AM during a power outage.
If you're serious about backup power, get your unit from a Generac generator authorized dealer, size your propane tank for at least 7-10 days of continuous operation (not just a weekend), and learn how to test for voltage with a multimeter and safely use a tool for fuel pump removal. And don't forget about the dual function circuit breaker requirements. Build in some buffer—trust me, you'll sleep better.
