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How Long Can You Run a Generator Continuously?


What’s the one electrical item that you dread the thought of not being able to use?

For us, it’s probably the cell phones we rely on so heavily day-to-day (hence why they’re nearly always paired up to the mains if we aren’t out and about). For others, it could be their televisions or laptop computers.

Whatever your answer, they say that absence makes the heart grow fonder…but we’re calling BS on that.

After all, if like us, you’ve ever experienced the misfortune of being unable to use your tech over a prolonged period, aside from the relentless boredom that ensues, it can feel like society has temporarily returned to the dark ages.

Thankfully, from letting you charge your phone at the campsite to providing backup power in the event of a power outage, generators are a great source of temporary power that can effectively bridge the gap until normal electrical service resumes.

an image showing a generator charging a phone

Even if you aren’t the camping type, a generator is still a worthy addition to your emergency planning provisions.

Don’t believe us?

Well, consider the fact that there were 3,526 reported power outages in the United States in 2017 alone. While this might have been fewer than were reported in 2016, the number of people affected doubled from 17.9 million to 36.7 million, showing that it’s an issue that continues to affect more and more people.

With increasingly erratic weather patterns becoming normal throughout the world, too, the threat of a power outage is never far away.

While the average power outage in 2017 lasted only 81 minutes, the risk is that you could be relying on a generator for several hours, days, or even weeks,

Because of this, we thought it would be worthwhile to address the question – how long can you run a generator continuously?

Regardless if you already have a generator, or you’re deciding which model to purchase, it’s an important question to answer.

So, without further ado, let’s do precisely that…


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Important Points to Consider

Before we begin, it’s probably a good idea to cover how you should and shouldn’t use generators.

Firstly, it’s worth mentioning that generators are ideal for situations where power is needed short term.

In other words, you should use a generator as a backup power source only.

It’s also worth mentioning that you shouldn’t use a generator continually, for example, over weeks or months, without periodically switching it off (something we’ll discuss in more detail shortly).

Finally, while you could, in theory, use a generator as a primary power source, in other words, as a permanent substitute to your mains electric, there are a few reasons why this isn’t a good idea:

  • Generators Have a Finite Lifespan
  • Unsurprisingly, generators won’t last forever. The exact lifespan will between models, and will depend on factors like how well it has been maintained, and how much it has been used, for example.

    Regardless, swapping out a generator every few years will likely be far more expensive than installing and maintaining a permanent power supply.

  • They’re More Expensive to Run (Than Grid Power)
  • From a financial standpoint, fueling a generator with the most commonly used fuels (petroleum, diesel, and liquid petroleum gas, or LPG) will cost considerably more than the average permanent power supply.

    For context, Mr Electric found that generators can cost anywhere from $52-$200 per day to run depending on fuel type, compared to an average daily grid power cost of just $3.72. Quite the difference!

  • Generators Can’t Be Used Non-Stop Over Long Periods
  • First and foremost, there’s the fact that whichever fuel you’re using will eventually run out, and because you should never refuel a generator that is still running, you’ll need to stop it to refuel it once it has cooled down.

    Secondly, just like a car engine, a generator will require on-going maintenance, for example, checking and topping-up the oil periodically; otherwise, it’ll be prone to failure. As with refuelling, this will entail stopping the generator.

So, you now know that you shouldn’t use a generator as a permanent power source and that using one in this manner could become very expensive.

We still haven’t answered the burning question, though…

Just how long can you run a generator continuously?

As always, the answer isn’t a simple one, and it’ll largely depend on which type of generator you have or intend to buy; a portable generator or a standby generator.

Let’s answer the question for each type.


How Long Can a Portable Generator Run?

Owing to their smaller size (portable by name, portable by nature, after all) portable generators such as the WEN 56200i (shown below) are usually capable of running for the least amount of time.

When it comes to answering the question - how long can you run a generator continuously - a portable generator will generally have the shortest possible usage time. This image shows one such generator, the WEN 56200i portable generator

While there are portable generators that are fueled by diesel and propane, the vast majority use unleaded gasoline.

You’ll need to stop a generator when conducting maintenance, for example, topping up oil, so this automatically limits the potential of using a portable generator non-stop.

Fuel efficiency is another factor that plays a big part in how long you can use a portable generator (with diesel being the most efficient and capable of running for longer under the same load as similarly-sized gasoline engines, and propane being the least efficient), but the main limiting factor is the size of the fuel tank.

Portable generators fuel tanks can hold anywhere from 1-gallon in the case of models designed for carrying, all the way up to fifteen gallons or more in models with wheeled frames.

A standard 5-kilowatt gasoline generator typically consumes about 0.75 gallons of fuel per hour, giving anywhere from 1 hour 20 minutes all the way up to 20 hours runtime based on the examples above.

Here are a few more examples:

Table – How Long Can You Run a Generator Continuously?
Fuel TypeExample Generator SizeTypical Fuel Consumption (source)Example Fuel CapacityApprox. Estimated Runtime
Gasoline5-kilowatt0.75 gallons per hour1-gallon1 hour 20 minutes
15-gallons20 hours
Diesel20-kilowatt1.6 gallons per hour1-gallon38 minutes
15-gallons9 hours 23 minutes
Propane20-kilowatt3.45 gallons per hour20lb tank containing approx. 5-gallons1 hour 27 minutes
100lb tank containing approx 25-gallons7 hours 15 minutes

As discussed, you should always stop a generator to refuel it, and so the maximum this tells us how long you can run a portable gas-powered generator, on average.

You can complete a quick and easy calculation for your generator by simply dividing the fuel tank capacity by the typical fuel consumption figure, both of which should be provided by the manufacturer.


How Long Can a Standby Generator Run?

As mentioned, a portable generator generally can’t be used for longer than a couple of days.

In situations where you require backup power for longer periods, for example, over a couple of days in length, a standby generator is probably the best option.

Standby generators, such as the Generac 70361 model shown below, work as a backup electrical system, and they automatically kick in should the supply from the power grid fail. Once the power grid supply resumes, the standby generator automatically swaps back, and the generator then enters standby mode.

When it comes to answering the question - how long can you run a generator continuously - a standby generator will have the longest possible usage time. This image shows one such generator, the Generac 70361 home standby generator

Standby generators typically have much larger fuel tanks for starters (mostly diesel, natural gas, or LPG), meaning they don’t need to be switched off and refueled as often.

Some standby generators are even connected to piped natural gas, removing the need for refueling altogether.

They still won’t be able to be used non-stop permanently, though, as switching off to meet regular maintenance requirements, and the manufacturer’s guidance for maximum usage times will still apply.

The maximum run time will depend on the manufacturer; for example, CK Power recommends that standby generators run no more than 200 hours per year at an average load of 80% of their maximum-rated output.


Tips for Finding a Long Running Generator

While standby generators may be the best choice for backup power over extended periods, their costs (anywhere from between $2000 to $20,000, on average) can place them firmly outside the budget of the average homeowner.

Because of this, we thought it would be a good idea to provide some tips when it comes to sourcing a long-running, portable generator instead:

  • Choose a Diesel Generator
  • As mentioned above, diesel generators are the most efficient type available, meaning they’re capable of running for longer under the same load as similarly-sized gasoline engines.

    Propane-fueled generators are less efficient still than those fueled by gasoline.

  • Choose a Generator With as Large a Fuel Tank as Possible
  • Because you shouldn’t refuel a generator while it is running, one way to ensure that you maximize runtime is by choosing a generator with the largest possible fuel tank.
  • Check the Manufacturer’s Recommendations
  • Different manufacturers will stipulate different recommended runtimes. Check the specs and stats of each model before purchase to choose the one that allows the longest continuous usage.
  • Consider Using a Propane Generator With Multiple Fuel Tanks
  • Although, as we’ve mentioned, propane isn’t the most efficient fuel type for use in generators, if runtime is your primary concern, you can maximize it by hooking up two tanks to a single propane generator.

    The process works by fitting a changeover regulator to the gas line feeding the generator, off of which two propane tanks can be connected.

    The changeover regulator can direct propane from the first tank for starters, and then once empty, it can direct propane from the second tank at the turn of a dial. You could then replace the first tank to provide a continual supply of propane for longer running.


Frequently Asked Questions

  1. How much fuel does a generator use?
Click here to check out the typical fuel consumption rates for gasoline, diesel, and propane generators.
  1. How long will a generator run on 5 gallons of gas?
Click here to see typical generator runtimes.
  1. Can I run my generator all night? / Is it safe to leave a generator on all night?
Provided your generator is capable of running for eight hours, then yes, it should be able to run all night.

For example, it will need to be able to hold enough fuel to handle the level of fuel consumption to power whatever load you will be applying to the generator. It will also need to be rated by the manufacturer to run for that length of time continuously without being switched off.

In terms of safety, follow the manufacturer’s safety guidelines fully, making sure that the generator vents away from the house in an area with proper ventilation, and is used clear of any combustibles as an absolute minimum.

  1. What is the lifespan of a portable generator?
The average lifespan for a portable generator, measured in runtime, is anywhere between 10,000 and 20,000 hours.

Therefore, if you’re using it for 100 hours a week, you can expect it to last anywhere from two to four years.

Of course, these are ballpark figures, with the actual number depending on how heavy a load you regularly place on the generator, and how well-maintained you keep it.

  1. Can you refuel a generator while it is in use?
No. You should never refuel a generator while it is in use.

Generators can run hot even on a lighter load, and the combination of heat and fuel poses a significant fire risk.

Always switch off the generator and wait for it to cool down before adding fuel.


Final Remarks

If you take away one thing from this article, let it be that you can’t view a generator as a continual power source.

Yes, as we’ve shown, some generators can run for days at a time. Like any other mechanical item, though, and particularly ones with engines, they need on-going maintenance and the chance to cool-off after particularly lengthy usage periods.

Always remember to follow the manufacturer’s guidelines, and read the instruction manual thoroughly to avoid any safety or maintenance issues down the line.

If you have any additional questions or queries, leave us a comment below, and we’ll get back to you as quickly as possible.

Good luck!


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