Information & Advice

How Long Can A Generator Last If Run Continuously?

There are two main types of generators – standby and portable. Let’s have a look at both types and the considerations for each one.

Standby Generators

Many people in the colder states opt for a standby whole-house generator as a backup

Standby (or backup) generators are usually permanently installed and will be used in the case of a power outage. These are usually connected up to natural gas lines which means that they do not have a fuel tank, and instead have a constant supply of fuel and thus can run indefinitely.

Fuel Tank Size

Some standby generators are run on liquid propane or diesel and in this case the size of the tank becomes important. If this kind of generator is used to power a home, it will typically burn 2-3 gallons per hour. Therefore, a 500 gallon tank should be able to power an average home for around a week.

However one thing to bear in mind is that the size of the tank can actually be somewhat misleading, as they tend to hold a maximum of only 80% of the stated capacity. This means that a 500 gallon tank will only hold a maximum of 400 gallons at one time.

Even if your standby generator is capable of running for many days at a time continuously, you may wish to find an opportunity to switch it off periodically (such as some time during the night) so that it can cool down as a lot of heat will be created. The faster the engine, the hotter the generator will run.


As well as burning fuel, the engine of the generator needs oil to run. It is needed both to lubricate the engine and it also acts as a coolant to minimize wear and tear.

Oil is constantly being broken down as the engine runs and it needs to be changed on a regular basis – typically for every 50 hours of operation. However this also depends on how much oil your generator holds. The smaller the oil capacity, the more often it needs to be replaced.

Portable Generators

A portable generator will need frequent re-fuelling if used for long periods at a time.

A portable generator will run until it runs out of fuel. Like with standby generators, they can generate a lot of heat and it is good practise to shut them down periodically to cool off.

You can also use this time to check the oil, the air filter, the belts and anything else that needs to be maintained. By allowing it to cool off for around 30-60 minutes after every 6 hours of running you can ensure a healthy generator which should not overheat.

Unlike whole house generators, portable units are not really designed to be used continuously. They are more for short term or emergency situations. Please make sure you check the advise given for the particular make and model that you have!


The load that the generator is running will greatly affect how long it can run for. If you are frugal and can cut your consumption by half, then you will double how long the generator will operate for. This is also true for standby generators that use a fuel tank though it is less of an issue.

However, with portable generators in particular you must be careful not to run it under too high a load as this could damage it. When you calculate what size generator you need, you should always aim to buy one with a capacity that is around twice as much as the load that you tend to run most of the time. This means it will run at around 50% load which is ideal.

If you need to run a heavy load, it will vary from one manufacturer to another, but most will suggest that you limit operation at high loads to no more than 2 hours.


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