How Long Can a Generator Last? Factors that Influence Runtime

Ah, the ultimate question, “How long can my generator run?”

The truth is: there’s no simple answer to this inquiry. There are a number of factors that will influence how long your generator will continuously run after its fired up as well as its lifetime before ultimately calling it quits.

Let’s look at the factors affect your geneator’s runtime:

Portable vs. Standby Generators

The first follow-up question we have for you is: are you wondering how long a portable generator can last, or how long a standby will run— because these are two completely different beasts.

If you are unclear on the difference between a portable generator and a backup unit, read our other post on how standby generators work. We address how standby/backup generators are permanent features, attached to your home and  ready to fire up the instant your power is lost, while portable generators must be manually pulled out and fired up during an outage.

Standby units are generally larger than portable units, with drastically varying wattages and fuel feeding methods. Backup generators are at a huge advantage, as they are designed to power your home for days on end, while portable generators are engineered to get you by for a few hours and not a realistic solution for long-term electricity. Check out our Backup Generator Guide’s “When to Choose a Standby vs. Portable Generator” section to understand why.

Liquid Propane vs. Natural Gas

The next follow-up question we have is: are you asking about a liquid propane (LP) or natural gas-powered (NG) generator?

If you’re talking about a standby NG-powered generator, you’ll be tapped into an underground fuel line with unlimited access to your natural gas. Since these underground lines are controlled by the township, you don’t have to worry about filling up a tank like you would with a LP-powered unit and these generators can typically run up to 200 hours continuously without problem. (Keep in mind, if your natural gas line is damaged during a natural disaster, your access to fuel may be limited or restricted).

With a liquid propane unit, you’re at the mercy of your fuel tank size and the availability the propane company’s delivery availability. Meaning, while your generator might be willing and able to run continuously for a few days, if it sucks up all its juice, it’ll have no fuel to power itself until you refill the tank. Typically, a 1-2 gallon fuel tank can last from 8 to 10 hours (though wattage influences this as well), so if you want a few days worth of backup power, you’ll need a lot larger of a tank.

Keep in mind too that filled propane tanks only hold 80% of their rated capacities, so a 500-gallon tank stores only 400 gallons of fuel. Read all about the pros and cons of propane vs. gas generators here.

Wattage Requirements

This point seems pretty straight-foward: larger generators require more fuel than smaller generators. If you purchase an 11 kilowatt (kW) generator and use it to full capacity, it’s going to use less fuel than a 20 kW unit running at full capacity.

Powering higher-wattage household items and a higher quantity of items also requires more fuel. For instance, your electric water heater might need 4,000 watts, while your WiFi and cable modem only 40; the water heater is going to eat up more fuel. And the more items want to run, the higher your wattage needs grow.

In our other article, “What Size Generator Do You Need? Whole House Generator Sizing Made Easy,” we outline examples of household appliances by wattage to help you to determine your home’s wattage requirements.

Generally speaking, your generator operator’s manual should tell you how much fuel your unit will drain per hour when operating at full capacity. Use this data to help calculate how quickly you’ll deplete your supply.

Durability & Warranty

Then there’s the other side of the big question: when you say how long will a generator run, do you mean over its lifetime?

While some generator manufacturers offer lifetime warranties on certain parts of or your entire generator, this generosity isn’t common. Most reliable and reputable brands offer anywhere from 5-10 year warranties or promise to provide 3,000 to 5,000 hours of power.

With proper care, your machine can last for many years no matter your level of use.


Even generators with great warranties can fail to start with lack of routine maintenance. Your generator may fail to run if you don’t fire it up every few months; this keeps the electric starter’s battery fresh and charged.

We also recommend checking for rust, oil changes every 50 hours, filter replacement and other handy generator maintenance tips found in our other post. While paying for a yearly check-up on your generator will cost you, it could cost you more down the road to neglect your investment.

Get the Long-Lasting Power You Need

Now that you understand a few of the factors that influence generators’ continuous runtime and overall warranty, it’s time to start hunting for the right unit.

Here at SWFL Electric, we’re proud to be Kohler, Generac and Cummins dealers. Ask us to help you pick the best generator for your wattage. We’ll set you up with a lasting power unit to rely on for many years to come.

Explore our generators here.