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How Long can Generator Run? (Find Out Now!)

How Long can Generator Run? (Find Out Now!)

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Everyone in the whole wide world has, at some point in time, experienced a power failure. Some a few hours, some a few days or even weeks, depending on the situation at the power plant. Living without electricity for even a short period is a challenge, as we have grown so accustomed to having electricity all the time. Consider yourself lucky if you own a generator. Some generators can run for hours, others for days and even weeks on end, depending on the type of generator.

According to most manufacturers, standby generators can continuously run for 500-600 hours (21 days). Mostly due to their stronger engine designs and larger fuel tanks. Portable generators running time differs between 8-32 hours, depending on the size of the fuel tank, fuel type, and power output.

Generators can run for many hours on end, and if you make sure to supply them with fuel and oil, they will go on and on. That is until their engine seizes or stutters to a halt. Like most machines, they should not be overworked. Generators are there in case of emergency and require regular rest and maintenance. This article will discuss how long a standby generator can run, the portable generator’s running time, and what factors affect running times.

How Long Can your Generator Run?

Like all machines, generators are not designed to run continuously until the end of time. It is intended to be a source of backup power in times of need and to provide you with power when in an area where there is none. Some portable generators can run for 8-12 hours, others for 12-32 hours, while certain standalone generators can run for days or weeks, highly dependent on the size of their fuel storage.

The best and most effective way to calculate how long your generator can run is to follow the manufacturer’s recommendations. These companies build generators for a living; they have the most solid idea of how long their generators can run without damaging the engine. Like any machine ever made, generators require lubricants, fuel, and regular maintenance to help keep the engine going.

Generator manufacturers typically offer three to five-year warranties on their products. Some are marketed to give you between 3000-5000 hours of electricity, which indicates that it’s not built to last a lifetime, more likely somewhere between 10-20 years if well looked after. Running your generator all the time, with the necessary oil and fuel constantly supplied, doesn’t mean that your engine will not splutter and die at some point.

How Long Can A Standby Generator Run?

Standby generators can run for longer periods due to their robust engine design (especially the diesel models) and larger fuel capacity. A standby generator is a powerful soldier to have on your side when extended outages hit your area.

Standby generators typically run on:

  • Natural Gas
  • Liquid Propane
  • Diesel
  • Gasoline

Generators that run on liquid propane will usually be hooked up to 500–1000-gallon tanks, which helps them run for a long time without refueling. Natural gas generators have an endless supply of fuel; it’s just the lubricant part that needs to be monitored when running for longer periods. Diesel generators are your most powerful type due to the strong and fuel-efficient engine design, and it’s also the cheaper fuel option.

 Most standby generators, according to their manufacturers, can run continuously for:

  •  500-600 hours, or 21 days.

For these longer-running standby generators, regular maintenance is an absolute must to ensure longevity. Although they can probably run for more than the recommended time frame, you should consider the overall impact on the engine if this is a regular occurrence. After every long-running session as listed above, be sure to give the generator a bit of a rest and perform some maintenance (oil and filter changes).

How Long Can A Portable Generator Run?

Portable generators are designed to run for shorter periods as their fuel tanks are not as large as their standby counterparts. A portable generator is not intended to run for days, weeks, or months without stopping. It generally runs until the fuel runs out!

Most portable generators have a typical runtime of between 8-20 hours, depending on the power output, type of fuel, tank size of the unit, and engine oil levels. A common metric that you will often see and hear about is “run time at half-load.” This measurement indicates how long a portable generator can run on a single fuel tank at half of its power capacity.

Power Output

A common metric that you will often see and hear about is “run time at half-load.” This measurement indicates how long a portable generator can run on a single fuel tank at half of its power capacity. As a general rule, you would want a portable generator to be able to provide you with at least 10 hours of running time while operating at half-load.

It will give you the luxury of sleeping through the night without the hassle of refueling it until the morning. Let us look at the following example:

  • A 5000-watt generator that has a 12-hour run time at half load will provide 2500 watts for 12-hours.
  • Running this same generator on 5000-watts (full load) will reduce the running time to 6 hours.

Tank Size

The size of the portable generators fuel tank also plays a big role in how long it can run continuously. The bigger the tank, the more fuel there is to run on and generate the required power.

One of the longest-running portable generators on the market is the diesel-powered Generac 6864:

  • It has a tank that takes 12-gallons of fuel, and while running on half-load, can provide you with 32-hours of continuous running.

For safety reasons and to make sure that your portable generator will last as long as the manufacturers indicated, it’s recommended that you don’t run it for more than 48-72-hours at a time without resting the generator. Just like any piece of machinery, it will start to take a beating with regards to wear, tear, and over-excursion when you don’t switch it off and let it rest.

Engine Oil Levels

Engine oil levels play an essential part in the run time of a generator. The generator needs oil to lubricate and cool it down while switched on. Running your generator with a low oil level will dramatically decrease its running time.

Most modern generators have a switch that shuts the engine off when the oil goes below a certain level (normally between 150-200 hours of runtime). A good rule to follow is to change the oil after every 100 hours of use.

Type of Fuel

The types of fuel that generators use is the following:

  • Diesel
  • Gasoline
  • Propane
  • Natural Gas

Diesel is your heaviest fuel type, while natural gas is the lightest. Heavier fuel types allow for longer run times. A gallon of diesel will have a longer runtime than a gallon of gasoline, propane, or natural gas. A diesel generator is normally much bigger and stronger than another generator running on other fuel types.

Generators that run on the above-mentioned lighter fuels require less robust parts in their engine design, which in turn require that the machine needs to take more frequent breaks compared to heavier engines that run heavier fuels. The lighter model generators also require more maintenance than the diesel models.

Lighter-fueled generators also have a shorter runtime due to safety issues. When refueling a generator that runs on light fuels, you have to shut off the engine and let it cool down before refueling (it is not safe to refuel while the generator is running). However, you can refuel a diesel generator while it runs, prolonging the runtime. Most portable generators running on light fuels tend to produce excessive heat after 12-24 hours of running and may lead to engine damage if pushed further.


Standby generators are designed with more powerful capabilities and larger fuel tanks, so it’s a no-brainer that they outrun their portable counterparts with smaller engines and fuel tanks.

Most standby generators can easily complete a 21 day (500-600 hour) continuous run before needing some rest and maintenance. Standby generators generally run until their fuel has been depleted (8-12 hours) depending on the fuel tank size, the power output of the generator, as well as the oil level and fuel type it’s running on.

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