Question Marks

How Long Can Standby Whole Home Generators Run?

No one is a fan of the power going out in their home. It is never expected and when it does occur you are left without so many things. In today’s world it seems that everything takes power rather it be your phone, computers, television, refrigerator, furnace, and air conditioner. If you live in an area that is prone to power outages rather it be due to blizzards, high winds, or hurricanes then it may be worth looking at purchasing a standby generator whole home system.

These standby systems can power your entire home automatically at the first sign of your power going out. In most cases when the power does go out you will see a flicker of the lights for a second or two and then presto, your standby system is now on and providing power to your home. There are other options out there to provide your home with emergency power, but standby systems are going to be your most reliable and most efficient.

How Long Can They Run?

A common question on these standby systems though is how long can they run? Lets say that you live up north around one of the Great Lakes. While I live in Kansas now I grew up around Port Huron and know exactly how much snow that can happen in just a days time. In many cases this extreme snowfall can lead to power outages… sometimes for days at a time depending on how remote you are.

My grandfather has a home up by Bad Axe, Michigan and every year he loses power during the winter. Luckily, he has a wood furnace to warm his home, but what about his other appliances? He did not want to sit around and wait for the power company to make their way out so he opted for purchasing a standby generator system from Generac. One of the questions that he had before purchasing a standby system was how long it could run during these longer power outage events?

In theory a standby whole home generator can run indefinitely. To answer my grandfather’s question though we first need to understand what fuel type your standby system is. The length of a time a unit can run all depends on the fuel that the generator takes. Most standby systems have three different fuel choices to choose from. Diesel, Liquid Propane, and Natural Gas. I listed these from shortest lasting to longest.

Diesel standby units are typically the shortest lasting units due to the limitation of their fuel tank. You can only store so much diesel in your fuel tank before you run out. In most cases a diesel standby generator can last between twenty-four hours to seventy-two hours of constant running before your fuel supply runs out.

The next option, our middle of the road selection, is liquid propane or LP. Now an LP generator is again limited by its fuel tank BUT an LP fuel tank is typically much larger then a diesel tank. As an example, lets say you have a five-hundred gallon LP tank filled up to capacity at four-hundred gallons. With that amount of fuel on hand you can expect your generator to run for a solid week, or seven days. You may even go slightly over that amount. If you are in a situation with an extended power loss be sure to reach out to your local fuel supply company to arrange top-offs or refuels during the power outage.

For many of us out in the country diesel or LP are the only options that we have to choose from. Being rural is nice but often times you are limited. As an example, the third option to fuel your standby generator is natural gas. The only real downside here is that you have to have a natural gas line routed to your home. The good news is that if you do then your standby system can run indefinitely as the fuel is constantly being fed in from the city’s utility company. As long as you are willing to pay for the natural gas then you will never run out.


If you are going to be running your generator for an extended period of time then I need to mention to you the importance of oil. Just like with any engine oil is the lifeblood of your generator. Without oil your generator can overheat and even catch on fire. Oil cools the engine. Oil provides lubrication. Oil promotes a healthy life of your generator. Through extended use the engine will burn oil. It will happen.

If your generator is running for an extended period of time then the engine can overheat. When the engine overheats more oil is burnt. Most professionals recommend turning off the generator periodically to let it cool down. This should be done once every twenty-four hours. During this cool off period you can also check the oil level of your generator’s engine. This is vitally important. Without adequate oil you could seriously harm your standby system.

Do NOT put oil in the engine while the engine is still running… or even while the engine is still hot. It is always best to wait for it to cool down before adding oil. Also, when adding oil to the generator be sure not to overfill the system. This can cause a whole other host of problems. It is best to have just the right amounts of oil. Depending on how long the generator has ran you may also need to do a complete oil change. Manufacturers typically recommend oil changes after about two-hundred hours of operation.

Generator engines come in two different categories. There are the thirty-six-hundred rotations per minute and then the eighteen-hundred rotations per minute. The eighteen-hundred models run cooler and use less oil then their counterparts. If you are expecting long term power outages then it is recommended to go with the eighteen-hundred RPM unit over the thirty-six-hundred. Note though that the eighteen-hundred models are going to be more expensive.


As I stated previously in this article folks it is all going to depend on the fuel type of your standby system. If you have not already purchased a standby system yet then I recommend that you review all of your fuel options before purchasing. Personally, I am the biggest fan of liquid propane. With LP you are not reliant on the city’s natural gas supply and if you plan ahead you should have your LP tank completely full and ready for emergencies.

In fact, many folks have a separate LP tank installed JUST for their standby system. Their other LP tank would be used for their day to day activities such as using the oven, water heater, and furnace. In my opinion this is the smartest way to go about it. But, as always, ultimately the choice is up to you.

Thanks for reading,

Alec Johnson

You may also like