So, How Long Can You Run a Generator For?

A generator is one of the single best preps you can have, for virtually any disaster situation.

a gas generator
a gas generator

Whether you have a small, portable generator capable of running an appliance or two or a large, built-in standby generator that can power your entire house, you’ll be able to keep the lights on when no one else can.

However, a generator is only helpful so long as it is running. How long can you continuously run a generator for?

A small, portable generator might only run for 24 to 72 hours with constant refueling while larger standby generators can run for 200-300 hours so long as their fuel supply holds.

The type of fuel that a generator uses along with the quantity of the connected fuel supply, rating of the generator, general state of repair, and other factors all play a part in determining how long you can safely keep your genny running.

Overworking a generator is a great way to damage or destroy it, plunging you back into the darkness and back to square one as far as your personal power infrastructure is concerned.

A more thorough understanding of the various factors associated with generator uptime will help you make an informed decision for both equipping yourself with a generator and making the best use of it. We will discuss these factors below.

Types of Generators

The two main types of generators are portable and standby and while they both provide power, they are very different in how they do it.

​Portable Generators

A portable generator is a great tool to take with you truck camping or in RVs; they will not power an entire home. You can find them as propane or portable gasoline generators.

They are not intended for long-term use as a fuel tank will only last up to 72 hours of use on a tank of gas. If the generator is running off of liquid propane tanks then you often have the option of attaching a hose to a larger 20lb tank.

Keep an eye on the oil levels as most manufacturers want you to top it up every 200 hours or so as proper maintenance. They have the smallest load capacity of the generator types and will power limited utilities.

Standby Generators

Standby generators are common for houses and facilities that can’t afford to lose power, such as factories or computer server rooms. How much power and the amount of time they can run are based on a few different factors, including:

  • How much fuel they can hold
  • Fuel consumption – Usually in liters per gallon (LPG)
  • Is it a single fuel tank or more?
  • How does it hold up in a storm?
  • What your usage requirements are

If you’re looking for backup power that can run for an extended period, then a standby generator is what you need.

There is a third type of generator that runs off natural gas. These generators are hooked up to natural gas lines giving them an unlimited fuel capacity. Natural gas generators will work during a power outage since the utility company substations usually have their own generators to keep the pumps working.

You’ll still need to change the oil every so often but the generator run times are incredibly long since there is no need to re-fuel. Since most people don’t have natural gas hookups, you don’t see these generators very often.

Warning: Most Generators Won’t Run Indefinitely!

Before we go any further, it is essential that all preppers understand most generators are incapable of running indefinitely, despite the fuel supply that you might have on hand.

Planning to simply kick on your generator after the lights go out and carry on living as usual for the duration, heedless of any hardware limitations.

Doing so is a great way to damage your generator. You definitely can’t afford that in the middle of a survival situation when you are depending on it.

It is imperative that you read and understand the manual and any other associated technical literature included with your generator to avoid this unhappy occurrence.

Fuel Supply and Type of Fuel

The type of fuel that your generator uses will play a part in determining it’s useful up time. Two of the most common and popular fuel types for generators today are gasoline and propane.

Both are highly energetic and both are generally efficient, but gasoline has a decided limitation and that the generator cannot be safely refueled once it has gotten hot should it run out of fuel.

Doing so might risk a calamitous fuel explosion at worst or an out-of-control fire at best. You can afford neither during a live event.

The nature of propane generators usually means they will be hooked up to a larger, on-site tank with a large capacity meaning that refueling is more of a logistical than a practical concern.

However, some smaller, portable propane generators can be fed from common barbecue cylinders.

For most models, these can be switched out even when the generator is hot so long as it has been shut down with little if any risk of mishap so long as correct procedures are followed.

Whichever kind of fuel you are using, the larger the attached fuel supply the longer the generator should be able to run theoretically before it needs to be shut down.

Diesel Generators

Diesel generators are some of the best generators you can buy as they provide maximum power with long-term use. Depending on the model a few gallons of fuel can last you several hours of continuous use. If you’re looking to conserve fuel then one of these might be your best option.

Propane Generators

Propane is easy to come by and relatively inexpensive for generator use. 20 lbs of propane can give you around 6.5 hours of runtime at 50% load. These generally come on wheels for easy transportation and can be purchased at your local hardware store.


The rating or size of the generator is another major determining factor in uptime, with larger generators almost invariably capable of running far longer than smaller, portable jobs. To a lesser extent, the nature of the generator also has a part to play in determining runtime.

A massive standby generator, or bank of generators, intended to operate a hospital or any other vital equipment in the event of a power outage made likely run for days or even weeks at a time depending on the requirements of the facility (assuming, of course, that the generators are in a good state of repair and have access to an adequate fuel).

A small, wheeled job site generator may only be good for several hours before it needs to be shut down.

Somewhere in the middle is a household standby generator, which might run anywhere from a day to a week at a time. This is where many people can go wrong by assuming that the generator can run indefinitely so long as it is fueled.

Heat Buildup

Heat buildup is a major enemy of generator performance, and is one of the chief limiting factors concerning runtime.

All generators build up plenty of waste heat as they operate, and depending on ambient conditions, the efficiency of the generator and other factors this waste heat could continually climb, and climb past safe operating limits.

When the temperature rises too high, a decision must be made. Some generators feature a built-in automatic shutdown switch activated when temperatures climb too high, whereas other generators must be manually shut down.

Many generators can continue to operate outside of their nominal heat range, but this usually comes at the cost of accelerated wear and the potential for catastrophic breakdown.

It must be noted that ambient temperature greatly determines how much excess heat will build up and how quickly.

Running a generator in a frigid climate will go a long way towards mitigating this excess heat, whereas running one in a steamy, arid environment will exacerbate the problem. Don’t forget to factor local conditions into your calculations!

State of Repair

The state of repair a generator is in also greatly determines its run time, and a generator that is kept in tip top shape will run longer, easier and more reliably than one that is in a rough and ramshackle condition.

Generators in a poor state of repair might have a decidedly reduced operational time that could come back to bite you in the butt when you can least afford such a setback.

Additionally, the vintage of the generator plays a part in this calculation, with newer, state-of-the-art generators benefiting greatly from enhancements in materials, design and management systems whereas older generators are usually simpler but far less refined and more likely to have limited operational capacity.

Both might be entirely adequate to your needs, even far more than adequate, but you must know what you are dealing with.

Maintenance Issues

It should go without saying that regular maintenance checks should be performed on your generator, and many manufacturers prescribe simple inspection or other maintenance protocols after running the generator for so many hours or so many tanks worth of fuel.

Don’t ignore these recommendations! The corporations that produce these devices have high-dollar teams of engineers that design and refine them, and they have put in the work to determine what a generator is capable of and, just as importantly, what it requires in terms of maintenance for long life and consistent operation.

So There You have It!

Most generators can run for quite a long time, but they cannot run forever, and operational time can be measured in as little as a handful of hours to as long as weeks on end without shutting down.

Uptime is affected by many factors, including the rating and fuel type of the generator along with its state of repair, overall condition, and accessible fuel supply.

A thorough understanding of what your generator is capable of under various conditions is essential for getting the most out of it when the chips are down.

3 thoughts on “So, How Long Can You Run a Generator For?”

  1. As an electrician and trained in electronics in the navy I understand the need for maintenance . having parts available that will predictably fail in a small generator many things will fail if like your car are not maintained. the simplest is oil oil degrades like gasoline changing it every year using it or not is a must. wait don’t toss that old oil out. put it in a sealed glass container that has little or no exposure to air. if your generator becomes low on oil adding this to it is a good option and will save an engine the whole idea for oil is to reduce friction and carry away heat even oil that is compromised by age will offer protection until regular oil can be obtained. oil additives is what degrades the fastest. additives can be purchased and stored to add life to old oil. take care not to buy the “magical mouse milk” that will cure all. they are worthless. look for the brand name item made by the large oil companies. bearings !!! present in both engine and generator. purchasing a generator with roller bearings will give you the longest life of your unit the generator also has “sealed ” bearings they also have limited lifespan. purchasing a set when your unit is new insures you get the correct ones when the others fail. parts for the engine that consist of a carbonator rebuilding kit or an entire carbonator which is what I recommend because they are relatively inexpensive is a must. leaving gas in it all summer can gum it up making your unit an expensive paper weight. such simple things like hoses for your gas flow to the carb. a simple item that also renders a generator useless. using tubing unrated for gasoline can leak and cause a fire. while many items are needed, many can be substituted without danger, one that must be an exact replacement are the brushes for the generator. this item can be purchased at the time of sale because it is made of carbon and wont deteriorate over time. while using a stone to “dress ” the commutator insuring the brushes are seated giving the best connection and insuring the longest life for your brushes. Note, getting instruction on replacing and dressing with a stone ( do not use a stone to sharpen tools. many contain metal that will short out the connections and ruin your unit. Remember safety first. maintenance on your unit must be done disconnected from all sources of power and fuel sources !!! disconnected not just turned off !!! a practice that can save your life. it takes four milliamps of current to kill you. don’t be fooled because it is connected to low voltages. you must live to tell the tail of your power outage to your grandkids teaching them about safety. be safe! ——-Grampa

  2. I have a brand new, whole house Generac, 22kw rated… clearly states in the manual that the unit should have the oil checked “Daily if ran continuously”…I asked my installer what that meant, he stated somewhere from 24-30 hours, tops. He said that these units can go 2000 to 4000 hours before a large failure if you follow the owners manual and check/change the oil on time.
    (So no running it forever even if your gen runs on LNG).
    During the Feb 2021 ice storm I shut it down every 25 hours, checked the oil, topped it off if it needed it, and then restarted. I keep plenty of oil and two extra filters just in case.

  3. I think the important phrase here is “as long as fuel stocks last”.
    the chances are you will only be using a generator when the power grid has shut down or collapsed and if that has happened so have fuel deliveries to filling stations, which cannot pump fuel anyway without mains power.
    therefore any fuel stocks you have personally are finite, they only last as long as they do, after that you are in the dark same as everyone else.

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