What Size Generator Do I Need for My Sump Pump?

Having a generator on hand that will run your sump pump is a necessity as a home owner for when the power goes out. Power outages often come with heavy rains, and that can lead to disastrous flooding in your basement.

If you’re in the market for a generator and need to know what size you need, you’re in the right place.

A sump pump can be powered with a 2000-watt generator but a better option would be a 3,500-watt generator (or higher) to not overload the generator out when the pump kicks on while you’re powering other appliances or lights.

Below I’ll cover the power requirements of your sump pump as well as the critical considerations you need to make prior to purchasing your generator so that you don’t damage your sump pump, your generator, or some other appliance.

How Much Power Does a Sump Pump Require?

In general, you’re going to be dealing with either a 1/3HP or a 1/2HP sump pump. A 1/3HP sump pump will be about 600-800 watts while running, with start up watts around 1,300-1,600. A 1/2HP sump pump will be about 800-1,000 watts while running and will have start up watts ranging from 1,500-2,150.

The start up watts are important for the first few seconds of operation and then the pump will drop to the running watts. Starting watts are basically a higher surge to get everything up and running properly.

Think of riding a bike and starting to pedal. The first few rotations of your legs will take a lot of effort, but once you get going it barely takes anything to keep the pedals moving. It’s the same concept with items like pumps and compressors.

generator to power sump pump
Courtesy of Wikimedia Commons

Critical Considerations Before Selecting a Generator for Your Sump Pump

As we mentioned above, we need to keep in mind the starting watts when selecting a generator. Since there’s no way to really know the exact number that’s required for the start up watts without the help from an electrician, you will need to be conservative and size up to err on the side of caution.

A 2,000-watt generator is the smallest size that you will want to attempt to run your pump — especially if you have a 1/2hp pump. The starting watts of a 1/2hp pump may very well exceed the capacity of a small 2,000-watt generator. Even if it does start it, you’ll be putting it to the absolute limit by doing so.

I personally recommend going at least 3,500-watts or higher and here’s why: you will be reducing the stress on your generator by not maxing out its capacity, and you will be able to power other things such as lights and entertainment.

The danger with running items with a high start up draw is that you don’t have control over when they will demand it from the generator. So if your generator is powering the sump pump, it must be ready to deliver whatever the start up wattage is at any time.

If, for instance, you’re using a 2,000-watt generator to power your pump and you also decide to power your TV, laptop, and a few incandescent lights, you could easily be running an additional 300-400 watts. Let’s say you’re running 400 watts continuously by running those things and then your pump kicks on and demands 1,750 watts. You’re now exceeding the rated capacity of your generator.

maxing out generator capacity
You really need to be careful before you start plugging everything into the generator so you don’t forget about the starting watts of certain appliances!

If you’re lucky, it will surge and handle the draw for those couple seconds. If you’re unlucky, you can ruin your pump, TV, laptop (worst case scenarios) or pop a breaker on your generator (better case scenario).

A 3,500 watt generator would have been able to handle the situation comfortably.

Whatever you plan on powering, make sure that the total running watts are at least 25% below the rated running watts of the generator to keep from stressing out your engine. Your car is certainly capable of going 110mph, but you’ll probably get a lot more life out of it if you only go 60mph. The same applies to generators.

Also, remember that you may not be able to power two items or more that have start-up wattage requirements. If they kick on at the same time (or even if one kicks on after the other is already running), you can easily overload your generator.

Sump Pump Considerations Before Purchasing a Generator

You will definitely want to check and see if your sump pump simply plugs into the wall or if it’s hardwired to your breaker box. This may very well dictate how you go about purchasing your generator.

If it’s hardwired in, you’re going to need to hook your generator up to a transfer switch or back feed it (which I won’t recommend or explain). If you don’t know what you’re doing, do not attempt it and please consult an electrician or someone with a firm understanding of electricity to show you.

If your sump pump simply plugs in, you are going to want to take great care to select the proper cord diameter and quality to reach your pump with as little voltage drop as possible.

Generators have to be operated outdoors, and it might be tricky to navigate your cords through the house and down into your basement. If you are powering other devices as well then you’re definitely at risk of this.

As the electricity travels down the wires, it will drop in voltage the further it goes and may not be able to power your pump. If you are able to get the pump started but the cord isn’t thick enough or of high enough quality then you can overheat the wires inside and cause a fire.

Here’s an example of a quality cord that you can check out at Amazon. You’ll need to determine exactly what you’re wiring and how you plan on doing it (direct connect or transfer switch) before purchasing.

My Recommended Generators for Powering Your Sump Pump

If you’re looking for a solid workhorse that can power nearly everything in your house (though necessarily not all at once), then the Champion Power Equipment 7500-Watt Portable Generator with Electric Start on Amazon is well worth considering.

This comes with an electric start option so you won’t throw out your shoulder and back by yanking on the pull cord. It also sports a wheel kit for easy transport around your property. If you’ve ever had to move a generator, you know how this is a lifesaver!

It has a mid-range decibel level of 74 at 23 feet but you can easily take a few steps to mitigate that if you need to to make your generator quieter with an article I wrote. For reference, a 74-decibel reading is just louder than a blow dryer or busy city street.

A slightly smaller sized option is the DuroMax XP5500EH 5000 watt Dual Fuel Hybrid Generator with Electric Start on Amazon and it also comes with a wheel kit and lets you avoid the cardio-inducing pull cord.

It has a 69-decibel rating which is a little quieter than the Champion model but the human ear won’t be able to perceive a difference very well between the two with such a close decibel rating.

If you check out the DuroMax option, they have various other sizes on the same page that you can check out.

When considering generators, just remember that they are typically advertised with their “peak wattage” instead of their “running watts”. “Peak wattage” is the max limit of the generator and it can only sustain it for a very short period of time (to help with a sump pump’s starting watts, for instance). So, a 5,000 watt generator might actually have running watts of 4,250, for example.

It is best to select a generator where you won’t exceed 75% of the capacity of the running watts (the occasional surge above it is fine). Keeping your generator running at 75% effort or less will ensure that you won’t stress it out prematurely and run it into the ground.

Good luck with your basement and any flooding issues during the next power outage!

**Article’s Featured Image Courtesy of Wikimedia Commons

Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

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