All sump pumps have a maximum pumping capacity or flow rate, which refers to the total number of gallons that the unit can pump per hour. Maximum pumping capacity is an essential factor when installing a sump pump to ensure the unit can work effectively. If a sump pump doesn’t have a high enough capacity, it may not be able to pump enough water out of your crawl space or basement during heavy rains. This can lead to the pump basin filling up more quickly than the pump can handle, resulting in the basin overflowing and the surrounding area starting to flood. The capacity of the sump basin is also important in this regard as it is another factor in determining what size of sump pump you need. This guide will tell you everything you should know about sump pump capacities to help you determine what size of pump your home needs.

Pumping Capacity and Flow Rate

The maximum gallon-per-hour (GPH) capacity of a sump pump is primarily determined by two factors: the type of pump and the size of its motor. Sump pumps are either pedestal or submersible units. A pedestal unit sits on top or outside the sump basin, whereas a submersible unit sits at the bottom of the basin. Pedestal sump pumps tend to cost less, but they also usually have slightly smaller motors and are less powerful. Submersible pumps are almost always the better option for rainier climates or homes that are at higher risk of flooding.

Sump pump motors come in a range of increments from 0.25 to 1 horsepower. The maximum flow rate or GPH capacity of any size of pump can vary, as some units simply work more effectively than others. For instance, the flow rate of most 0.5-horsepower pumps is around 3,000 GPH, but there are some units of the same size that are more powerful and can pump nearly 4,000 GPH. The total pumping capacity you need is determined mostly by how much rain you get, how quickly the sump basin fills up, and the layout of the discharge pipes.

Understanding Dynamic Head and How It Affects Pumping Capacity

The layout of your house and the size, length, and design of the pipes that water is pumped through directly impact a unit’s maximum pumping capacity. Dynamic head is a term that refers to how far vertically and horizontally a sump pump has to move water from the basin until it discharges outside of the house, and dynamic head is the combination of the “friction head” and “static head.”

Static head refers to the vertical lift or the total vertical distance from the bottom of the basin until the 90-degree elbow where the pipe changes to run horizontally outside the home. Friction head is more complicated as it refers to how much friction the water encounters as it moves through the pipes and also the total horizontal distance the water has to travel. Smaller diameter pipes and longer pipes will increase the total friction head as will the number of pipe elbows in the drainage system.

Both the static head and friction head will also determine a sump pump’s maximum pumping capacity. Most manufacturers list two different capacities, the maximum total capacity and the capacity with a certain number of feet of vertical lift. You’ll also typically see the unit’s maximum total lift capacity and the maximum pipe length. All of these factors are important to determine if a pump has a high enough capacity to work effectively.

Most 0.5-horsepower pumps have a maximum vertical lift of around 7 to 10 and a maximum horizontal distance of around 25 feet. Some more powerful units have a vertical lift of up to 30 feet, but it’s important to understand that the total capacity will always be reduced the higher the vertical lift is.

A friction head typically isn’t something you’ll need to worry much about as long as the discharge pipes are properly installed and the system is designed effectively. However, static head or vertical lift is something you always need to take into account to ensure that the pump is powerful enough and has a high enough capacity.

Sump Pump Basin Capacity

A standard sump basin is 18 inches in diameter and anywhere from 2 to 3 feet deep, but some basins such as those designed for crawl spaces may be taller. You can also get a 24-inch diameter basin, and these are designed for much rainier climates, homes that are below the water table, or anywhere that is more prone to flooding. The size of the basin obviously determines its total capacity or how much water it can hold, and the capacity of the basin also influences what size or capacity sump pump you need.

If you’re installing a sump pump and basin in a home that doesn’t already have one, you’ll always want to have a plumber calculate what size of pump and basin you need. If you already have a basin and are simply replacing an existing pump, you’re normally fine to choose the same type of pump with the same horsepower as the old one as long as it always works effectively.

If you’re replacing your sump pump because it doesn’t always work effectively and doesn’t have a high enough capacity, you may want to take some additional steps to calculate what pumping capacity you need. This is something that will need to be done on a rainy day when the basin fills up fairly quickly and the pump needs to run often. To do this, you’ll need to first measure the total depth of the water in the basin. You should then unplug your sump pump or turn it off and wait exactly 60 seconds before measuring the water level again.

At this point, you’ll obviously want to turn the pump back on so that the basin doesn’t overflow before starting the calculations. In an 18-inch basin, every inch of water equals approximately one gallon, while 1-inch of water in a 24-inch basin equals around two gallons. Knowing this, you can then calculate how quickly the basin typically fills and what the total capacity of your sump pump needs to be.

If you have an 18-inch basin, all you need to do to calculate what capacity you need is to multiply the total number of inches the water rose in the basin in one minute by 60 to find how many gallons would normally fill the basin per hour. It’s always a good idea to multiply your gallons per hour measurement by 1.5 to make sure your new pump has sufficient capacity for extremely rainy conditions. Let’s say the water rose by 5 inches or around 5 gallons per minute. This means you’d normally get around 300 gallons of water per hour, so you’d typically want a pump with a capacity of at least 450 GPH.

With a 24-inch basin, you’ll first need to multiply the number of inches that the water rose by two to find the gallons per minute. You can then again multiply by 60 to find the average gallons per hour. Performing this type of calculation is important for ensuring that you choose a sump pump with a high enough maximum capacity so that it always works effectively and prevents flooding and water damage.

If you need to install or replace a sump pump, the team at High 5 Plumbing can help you determine what size pump you need and ensure that the new pump works effectively. We can also inspect your existing sump pump and service it as needed so that it always works effectively and when you need it to. Give us a call for more information on our sump pump services or if you need any other plumbing or sewer services in the Denver area.

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