How do I size a water pump? First, you need to determine how many gallons per hour you will need your pump to produce. Next, determine the head height. The head height is the distance between the pump and the highest point the water will be pumped to. Using these two figures, refer to a flow chart for the specific brand of pump that you are interested in, and choose the model that delivers the GPH you need at the appropriate head height. Next, you will need to make an adjustment to the size of the pump to compensate for restrictions that are placed on the pump. These restrictions include: elbows or sharp turns in your plumbing, in-line canister filters, and smaller-than-recommended outlet tubing. Typically, purchasing a pump that is one size larger than the model that you decided on in step one will allow for the normal restrictions caused by bends and elbows in the plumbing. However, if an in-line canister filter is being used, you may want to step up two models to compensate for this large amount of restriction. In either case, we recommend to install a ball valve on the outlet side of the pump so the water flow can be turned down if too large of a pump was installed. In other words, you can always turn down the water flow with too powerful of a pump, but you cannot increase the water flow if the pump you purchased is too small.
