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What Size Generator to Run a Sump Pump?

Run a Sump Pump
Written by Jamie Masterson

Most sump pumps for basements are either 1/2 HP or 1/3 HP.

A 1/3 HP sump pump requires around 1300 to 1600 watts to get started but keeps running at about 600 to 800 watts.

On the other hand, a 1/2 HP unit draws about 800 to 1000 watts to run, with start-up watts ranging between 1500 and 2150.

The start-up watts are only important for a couple of seconds of the operation. The pump then drops to the running watts.

Starting watts are essentially a higher surge to get things up and moving.

Invest in a generator that provides at least 20% more power than the starting wattage of your sump.

Generators don’t run at full capacity, so the extra power gives you more room to wiggle. Don’t push the generator at its max level or it will wear out sooner than your expectations.

One horsepower is around 750 watts but you want around 1.5 or 2 horsepower in power requirements for wattage allowance and load characteristics. In short, 1500 running watts are enough to run your single-horsepower pump.

You need to add more power to the equation when you run fans, lights, and other electrical items with the generator. Running a small refrigerator significantly adds to the power requirement.

Use a 16 gauge cord upto 50 feet long to run the sump and another similar cord to power up the appliances.

How to Decide on the Generator Size to Run Your Sump Pump?

Run time

Pick a generator that lasts more than the running time of your sump pump.

A generator with 7.5 hours run time in gasoline and 14-hour in propane gives you the option to settle everything in the house and collect fuel to keep the machine operational for a longer time.

Power output

Sump pumps use a lot of power to start up so check if the generator has the capacity to activate your unit.

The ideal method is to get a generator that surpasses the surge wattage of your pump.

A generator with 4000 watts of peak power and 3000+ running watts is a great choice for the job.

Control panel

Find a unit with a display that shows functioning parameters. The control panel lets you direct everything in the generator.

A multi functional control panel with necessary features allows you to take the right action on time.

Dual fuel mode

A generator that runs on multiple power sources gives you more room to breathe in catastrophic situations.

You won’t have problems operating the machine even when there’s a shortage of a particular fuel.

Noise level

Go for a unit that has a noise level under 60 dBA.

The buzzing noise of traditional generators disrupts the environment when you try to sleep or watch a film. The low noise feature has no drawbacks but it lets you reap all of the rewards.

You get priceless satisfaction and emotional reassurance when you know those pitfalls are avoided.

Number of sump pumps

sump pumps

Add up power ratings if you run multiple sump pumps.

This is especially important when you use machines with different horsepower ratings or from different brands.

The simplest way is to use the same type so you only have to multiply the required power by the number of units.


A generator that runs sump pumps costs higher than basic units but you should always abide by the budget when you choose one.

The price for a small reliable generator starts at $500 and goes up to $4,000 or more when you seek specific features.

A bigger portable unit that delivers at least 7,500 watts is ideal for big sump pumps and sensitive home appliances but comes at notably higher cost.

Portable or standby: What’s better?

A standby generator runs on propane or natural gas and costs higher than the portable type. The machine with over 8,000 watts delivered power comes in handy when there’s a prolonged power outage.

One drawback is that you need to hire a professional electrician to help with the installation.

A portable unit is a better choice when you want to save money on the purchase.

The price range is wide enough to match your budget and the maximum power output is 8,500 watts.

One thing you may not like is that the portable unit gets noisy when operated.

Quick tips to run your sump up with a generator

  • Set your generator at least five meters away from doors and windows to prevent the exhaust gas entering your house and keep the noise away. Get a gen-tent if you have to run the unit in rain
  • Make sure the generator is always clean and dry. Cleaning the machine and keeping it in a dry place helps maintain efficiency and durability. Always store a fresh fuel container and keep your generator lubricated
  • Fill up the tank and use the right cord before you use the machine. Start the engine afterward and connect the power cord when the generator runs. You will hear the sound of water being pumped away from your house
  • Secure your generator to prevent thefts. Consider the ease of mobility when you buy a portable generator
  • Install a second pump so that you have the option to run a second pump when one fails. You may also consider a standby generator with automatic transfer switch that allows for permanent installation and runs on natural gas. The setup lets you leave the house with no fear of a flooded basement when there are multi-day power outages
  • Heavy duty extension cords are expensive but a good option to run sump pumps. 14ga cords are good enough to run the pump and fridge. 12ga and 10ga cords are heavier but you don’t need to go the extra weight and expense unless the cords are over 100 feet long
  • Don’t waste your hard-earned money on a two-stroke generator at a low price since the power won’t be enough to start up a pump. You also need to consider branded machines over non-branded variants to make maintenance and parts replacement an easier job


Q. Are inverter generators better for a sump pump than conventional ones?

Inverter generators are a source of “clean power” that is ideal for sump pumps and other home electronics. They are portable but get noisy when operational. Conventional generators are a perfect power source but the non-portability and high harmonic distortion make them a lesser choice to run your sump pump.

About the author

Jamie Masterson

With decade-long experience as a generator technician, Jamie has worked with USA’s top generator manufacturers and suppliers as an independent contractor.

The long years of service to the industry has taught Jamie the ins and outs of troubleshooting, repairing, and maintaining all kinds of generators in home, industrial and outdoor settings.

Jamie thinks this platform is a great opportunity to share his tips and tricks with you so you can make the most of such power equipment for better living.

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