What Size Sump Pump Do I Need for My Basement?

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A sump pump can save you the trouble of a flooded basement. It moves water that gets into your home, whether from rain or groundwater tables, out of the structure and to an outside area where it can safely drain. Sump pumps come in various sizes. There are a few factors in determining the right sized pump for your home. Since there isn’t one rule of thumb to follow, you’ll have to rely on calculations and our tips for determining what size sump pump you need.

First, we’ll explain in general how to estimate pump size based on the unique characteristics of your home.

  • CapacitySump pumps are rated in how many gallons of water they can move in one hour. If the pump has too low a capacity, it won’t pump out water as fast as it’s coming in. If you don’t know it’s capacity, shut off the pump when it is raining, and allow the water in the sump pit to rise. A standard sump pit is 18 inches in diameter, so an inch of water accumulation is about 1 gallon
    • The formula to use is 1 x Water Accumulation x 60 x 1.5, which gives you an answer in gallons per hour (GPH).
    • If more water accumulates than predicted, a 24-inch diameter sump pit may be needed. Calculate 2 x Water Accumulation x 60 x 1.5 to obtain the required GPH capacity.
  • HorsepowerThe power of the motor is an important factor as well. Most homes are well-served by a 1/3 horsepower (hp) motor. If flooding occurs more frequently, a ½ or ¾ horsepower pump may be needed.
  • Vertical Lift (Static Head)This is how high the water must travel through the discharge pipe. The greater this distance, the harder the pump works. To measure vertical lift, calculate the vertical distance from where the water enters the pump to where the discharge pipe becomes horizontal.
  • Friction HeadFriction is generated as water travels through the discharge pipe; the pump must overcome this friction, which there’s more of the narrower the pipe is. Pipe fittings can increase friction too. Adding the friction head value to the static head value gives you the total dynamic head, which helps determine the required sump pump capacity.

Sump Pump Size for an Average Sized Home

If you have an average sized home with an average water table, you can use a 1/3 hp sump pump. It can usually handle 7 to 10 feet of vertical lift in a sump pit with one 90-degree elbow and 3-to-25-foot horizontal pipe run. However, if your water table is above average, use a ½ hp pump. It can move 35% to 40% more water and manage a higher vertical lift. You may need a higher capacity pump if the vertical lift is 10 to 15 feet or more and the horizontal run is 30 to 150 feet or more.

If the water table is unusually high in your area, such as if you live in a low-lying flood-prone location or a flood plain, consider a ¾ to 1 hp sump pump. Such devices can increase pumping capacity by up to 25% over a ½ hp pump and handle a vertical lift of up to 30 feet and horizontal run up to 250 feet. Higher-output systems are suited for outdoor applications as well.

 Get Help from a Professional Plumber

There are, of course, other factors to consider than sump pump size. It must be installed in the proper location, preferably the lowest point of your basement. Site preparation, taking steps to prevent clogs, the pump’s float valve, installation of the check valve, testing, and leak detection are equally important in ensuring the system works properly. At Hays Heating, Cooling & Plumbing, our technicians are familiar with every aspect of installing sump pumps in the Phoenix area (and will answer your question, “What size sump pump do I need?” Schedule plumbing service in your home by calling 602-641-4473 today.