How to Size a Hot Water Circulating Pump

Fitting a circulating pump to your hot water system is not complicated, but you must know how to properly size the pump. Getting the largest pump might not be the right solution if you have a small hot water system, but one that is too small can cause a lot of problems in obtaining hot water from your system. Circulating pumps work well with solar panels or with other forms of environmentally friendly heating, so if you have any green living hot water system, fitting one of these can help it to function like an ordinary hot water system. Before you purchase a circulating pump, you will need to work out the size of pump you need to fit the type of heater that you have.

Step 1 - Calculate Your Needs

The first thing that you will need to consider is how much strain you will be putting on the circulating pump. A large family will trigger the pump more often than a couple or a single person. The best way to work out how often you will be using the pump is to count the number of times that the hot water is used during a single day. Each time the tank is required to distribute water, the pump will be operating. This will give you a good calculation of how large your pump will need to be.

Step 2 - Air Leakage Pressure Test

Before you take the steps to install a pump, you will need to have the house checked for air leakage. A professional can do this for a small fee, and it is best done by an expert, so that you get an accurate result. Write down the results of this test and include it with the need calculation that you have performed. The amount of air leakage you get will limit the amount of hot water that reaches your taps, so you must add this amount to your overall use to get an accurate reflection of how much hot water you use.

Step 3 - Take Some Measurements

Measure the area beside your tank. Measure the diameter of pipes which will connect your tank to the pump, and also work out the amount of water which will travel towards the pump at any one time. Do this by removing the section of pipe where you will fit the pump and running the hot water through the pipe. Measure for a minute.

Step 4 - Calculate Your Needs

Circulating pumps should be sized to meet around 60 percent of the heating load, which is the calculation you have performed including water needs, leakage, and pressure. Fitting a pump to manage this amount of the load should give you 90-95 percent of the hot water needs for your home. Take these measurements to your pump supplier, and this should allow them to calculate the right amount of horsepower for your motor's needs.