Generator Fuel Consumption: How to Estimate Runtime

Reading fuel consumption on a listing

Generator fuel consumption is the rate at which a running engine uses fuel. On a product listing it usually appears as a runtime figure, such as hours per tank, rather than a per-hour amount. Listings on this site name the fuel, the type, the watts group, the start method and the features, but they do not state runtime or fuel use per hour. A watts figure describes what the generator can deliver, not what the engine will consume while delivering it. For a broad view of the types available, see the best portable generators guide.

Runtime figures belong on the maker's product page. A maker typically states runtime in hours at a stated load, and for a dual fuel or tri fuel unit the maker states a figure for each fuel. The first step in estimating runtime for a model is to find that maker's page rather than reading the listing. The best generator guide can help you shortlist models by stated details.

How load shapes fuel use

The link between load and fuel use is simple in principle. The engine burns fuel to turn the alternator, and the alternator delivers power to whatever is connected. The heavier the load, the more torque the engine must produce, and producing torque costs fuel. At a light load the engine turns easily; at a load close to the running watts figure it works much harder.

This is why a maker states runtime at a stated load rather than as one number. The same generator uses fuel at different rates at a light load, a half load and a full load. See the running watts vs starting watts article for how those figures relate to load.

• Running watts: the level the generator can sustain; compare your load against this figure.
• Starting watts: the brief extra effort a motor needs at start; it lasts moments and matters mainly for motors.
• Half load: a common reference load on maker pages.
• Full load: the heaviest the unit is built to sustain; fuel use is highest here.

Engine size as a signal

Some listings and maker pages state engine displacement. Displacement is a plain description of engine size, and a larger engine can deliver more power. At full load a larger engine generally consumes fuel at a higher rate than a smaller one, while at a light load the difference is smaller. The catalogue here does not state displacement, so an engine-size figure on a listing is a signal to read the maker's page, not a number to calculate from. Learn more about engine displacement as a listed term.

Reading runtime on the maker's page

The maker's product page is where runtime figures live. The page usually lists runtime in hours at a stated load, and for a dual fuel or tri fuel unit it lists a separate figure for each fuel. The page also states the tank capacity the runtime figure is based on and the fuel the unit takes. When you compare dual fuel models, see the best dual fuel generators guide for a starting point.

When you compare two listings, compare the fuel you plan to use. A gasoline-only unit has one runtime figure; a dual fuel unit has a gasoline figure and a propane figure; a tri fuel unit adds a natural gas figure. Read the maker's figures for the fuel you plan to run. The best tri fuel generators guide lists models that state three fuels on the listing.

Estimating for your own situation

To estimate runtime for your own use, start with the load you expect to draw and compare it with the running watts figure on the listing. Then find the maker's page for the exact model and read the runtime figure at a load near yours, per fuel. That figure is your estimate.

Home loads vary too much for a listing to carry a runtime promise. The U.S. Energy Information Administration reports that the average U.S. household uses about 10,500 kilowatthours of electricity per year, and actual use varies widely by region and type of home. For anything wired into a home, a licensed electrician and the maker decide the load question, and standby makers route installation through authorized dealers. See the home backup sizing guide for the questions to ask.

This site does not size a home or say which appliances a watts figure can carry. The guides compare stated details such as type, fuel, watts group, start method and CO sensor; runtime is a maker's figure. For whole-house wiring, the best whole house generators guide explains the standby category in listing terms.

• Note the running watts figure on the listing.
• Decide the load you expect to draw; for a home connection, ask a licensed electrician.
• Read the maker's runtime figure at a load near yours, per fuel.
• Use that figure as the estimate and check it against the maker's stated tank capacity.

Comparing fuel types by runtime

Fuel type shapes which runtime figure you read. The U.S. Energy Information Administration describes gasoline as a fuel made from crude oil and other petroleum liquids, and a gasoline listing carries a gasoline runtime figure on the maker's page. A dual fuel listing carries gasoline and propane figures; a tri fuel listing adds natural gas. The fuels differ in energy content, which is why the maker states a figure per fuel.

Fuel choice is also a question of availability in your area, which is a question for your fuel supplier. The catalogue cannot tell you which fuel to buy; it can tell you which listings name a fuel you can get. Makers such as Champion and Generac publish product pages and sizing tools for their portable and standby lines. The best gas generators guide focuses on gasoline-only units.

Why the catalogue stays quiet on runtime

The listings on this site are compared on stated details: type, fuel, watts group, electric start, RV ready outlet and CO sensor. Runtime and fuel use per hour are not among those details, so this site cannot publish a runtime estimate for any listing. A runtime figure requires the maker's own measurement at a stated load, on a stated fuel, with a stated tank capacity.

When you shop, use the watts group to shortlist listings and the fuel to narrow the choice, then read the maker's page for the runtime figure. That division of labor is why the guides compare stated details and why the maker's page is the source for runtime. For camping use, the best camping generators guide offers inverter sets in a size that suits a light load.

What to pick for your situation

Questions

Does the catalogue state runtime?

No. Runtime and fuel use per hour are not stated details on this site's listings. They appear on the maker's product page, usually in hours at a stated load, and per fuel for dual fuel and tri fuel units.

How does load change fuel use?

In general terms, the heavier the electrical load, the harder the engine works and the more fuel it burns. A maker states runtime at a stated load for this reason. At a light load the same unit uses fuel more slowly than at a half load or a full load.

Can this site calculate fuel consumption for me?

No. The site compares stated details such as type, fuel, watts group, start method and features. A fuel consumption calculation needs the maker's runtime and tank capacity figures, which are not in the catalogue. Read them on the maker's page.

Where do I find runtime for a dual fuel unit?

On the maker's page for that model. Dual fuel and tri fuel pages list a figure per fuel rather than one number. Read the figure for the fuel you plan to use, and compare listings on that basis.

Which watt figure should I compare against my load?

The running watts figure, which is the level the generator can sustain. The starting watts figure is for the brief extra effort a motor draws at start; it matters mainly when a motor starts, not for steady runtime.