Sump Pump Size Needed Calculation

Are you wondering what size sump pump you need for your basement? Do you know how to calculate Sump Pump Size Needed for Primary Sump Pump?

Sump Pump Size Needed Calculation is meant to help you determine what size of sump pump is required for your basement. Here are some of the factors to consider: type of soil around the house; elevation of house; square footage of house and roof; size of pit; vertical height water pumped up from the pit and pushed through the horizontal portion of the discharge system; number of fittings (elbows) in the vertical lift; number of horizontal feet of discharge piping to the destined location where the water is pushed to; and intensity of rainstorms.

How Does Type Of Soil Make A Difference In The Size Of Sump Pump Needed?
Clay soil requires a smaller sump pump than sand or top soil. If clay is found around the house, a flow of 8 gallons of water per minute per 1000 square feet of house is estimated. Clay is impermeable meaning it holds water better. If sand is found around the house, a flow of 14 gallons of water per minute per 1000 square feet of house is expected. Top soil flow is somewhere between 8 and 14 gallons per 1000 square feet of house. Sand and soil are permeable.

How Does Elevation Of The House Impact Rate Of Water Flow Into The Sump Pump Pit?

A house on flat land or in a lower position than surrounding land requires a larger sump pump. Water flow into a drainage system is decreased by house elevation. If the house sits higher than the ground around, less water will seep into the drainage system at a slower rate. Regardless of how high the house sits, the more slopped the soil is around the house downward toward the yard, the slower the flow of water into the sump pit. The flow of water is also decreased by a layer of clay like soil under the top soil.

How Does Square Footage Of House And Roof Impact The Size Of Sump Pump Required?
The larger the house and the steeper the room, the larger the sump pump must be.
The house with a larger foot print will cover a larger area for water seepage into the drainage system. A steeper roof will also increase the speed at which the water flows and the area from which water flows.

How Does The Sump Pit Size Impact The Size Of Sump Pump Needed?
One inch of depth in an 18 inch diameter sump pit equals one gallon of water. One inch of depth in a 24 inch diameter sump pit equals 2 gallons of water. Since it is best to keep the water below the drainage system pipe that comes into the pit, measure the distance in inches to the bottom of the drainage pipe; then monitor how many seconds it takes before the pit water reaches the bottom of the drainage pipe. This will indicate the pumping capability needed. For example, if it takes 15 seconds to fill the pit up to the drainage pipe which is 15 inches from the bottom of the pit, the sump pump will require a pumping capability of 60 gallons per minute.

How Does The Vertical Height Of The Discharge System Affect The Sump Pump Needed?
The vertical height of the discharge system, also known as the lift height, is the height of the discharge piping from the location when the discharge piping screws into the sump pump discharge port to the highest vertical point of the discharge pipe before the piping runs horizontally. Sump pump manufacturers advertise their sump pumps by gallons pumped per hour per height of the vertical lift. For example if the vertical lift was 9 feet and the pump needed to pump 60 gallons per minute, it would be necessary to install a sump pump that pumps at least 60 gallons per minute at a ten foot lift height.

How Do Fittings And Horizontal Piping Impact The Size Of Sump Pump Needed?
Fittings cause resistance to the water flow and thus require more pumping capability. Fittings include such things as check valves and elbows. One and a half inch check valves are estimated to cause 11.5 friction feet. Ninety degree elbows are estimated to cause 4 friction feet. Forty-five degree elbows cause an estimated 2.2 friction feet. If the discharge piping system had one check valve, one 90 degree elbow and 2 forty-45 degree elbows, the total friction feet would be 19.9. The inside of horizontal piping also causes a small amount of friction. If the horizontal length of discharge piping is 35 feet and the fittings friction feet is 19.9, the total friction feet would be 35 feet plus 19.9 feet giving a total of 54.9 friction feet. To convert friction feet to linear feet impact, 54.9 is multiplied by a friction factor of .201 since the discharge pipe is 1 1/2 inches in diameter. This leaves a total foot impact of 20 feet. If the horizontal piping is sloped down to the outside discharge point only the fittings cause a small amount of friction impact (4 feet). Some pump manufacturers label their pumps by the amount of vertical lift head. Others include both vertical lift and friction head. The method used is included in the pump specifications.

How Does Rain Storm Intensity And Frequency Affect Sump Pump Size Required?
The size of sump pump required needs to be calculated based on heavy storm rainfall amounts, intensity at which is falls, peak flow intensity and greatest storm lengths. Heavy, lengthy rainstorms and flooding are becoming more prevalent; therefore it is necessary to plan for the worst case scenario. Only a 1/2, 3/4 and 1 HP cast iron pump can keep up with lengthy, heavy rain storms.

Installing a heavy duty sump pump to handle heavy rainstorms has its challenges if there are many small rainstorms. A heavy duty pump will be too big for such storms; it will empty the sump pit too quickly because the ‘on’ ‘off’ point for the float switch is preset by the manufacturer. This will cause additional wear and tear to the pump motor. One solution for this situation is to purchase a non-automatic sump pump such as the Zoeller N98 and buy a variable level float switch will allow you to set a greater distance between the ‘on’ and ‘off’ position.

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