How to Calculate Fuel Needs for Your Whole-House Generator?

Determining Your Generator’s Power Output

When calculating fuel needs for your whole-house generator, the first step is to determine the generator’s power output. This information is usually provided by the manufacturer and is expressed in watts (W) or kilowatts (kW). For example, a 20 kW whole-house generator can supply a 5 kW load continuously, while a 10 kW load intermittently. Consider the number of appliances you plan to power simultaneously and choose a generator with a suitable power output. For example, a 10 kW generator can power a refrigerator, lights, and TV, while a 20 kW generator can power these appliances plus a water heater and air conditioner.

Calculating Run Time and Fuel Efficiency

Next, you need to calculate the generator’s run time and fuel efficiency. Most whole-house generators have a fuel efficiency rating of 0.5-1.0 gallons per hour (gph) at half load and 1.5-3.0 gph at full load. For example, a 20 kW generator may have a fuel efficiency of 0.5 gph at half load and 2.5 gph at full load. Multiply the generator’s power output by the run time in hours to determine the total energy consumption in watt-hours (Wh). Divide the total energy consumption by the generator’s fuel efficiency to estimate fuel consumption in gallons.

Example Calculation

For example, let’s say you have a 20 kW whole-house generator with a fuel efficiency of 0.5 gph at half load. You plan to power a 5 kW load continuously for 8 hours. First, calculate the total energy consumption: 5 kW x 8 hours = 40 kWh. Next, divide the total energy consumption by the generator’s fuel efficiency: 40 kWh / 0.5 gph = 80 gallons. This means you will need 80 gallons of fuel to power the generator for 8 hours at half load.