Solar Pool Heating Panel Ideal Flow Rate

Can You Run Water Through Solar Pool Heating Panels Too Fast Causing it Not to Heat Long Enough

In Education, Maintenance 2 Comments

This is always a good question. How fast should I run water through my solar pool heating system? Most think that running water fast through solar panels will not let them heat the water adequately. In fact, the opposite is generally true.

Solar pool heating panels work most efficiently when the difference between the panel surface temperature and the pool water is greater. As the pool water temperature approaches the solar panel temperature, the rate of heating decreases, making the panel less efficient. Most solar pool heating panel systems require an absolute minimum of 2 gallons per minute (GPM) per panel. Three to five GPM is a better target, depending on panel size. You won’t get much additional heating performance from higher flow rates.

Do not attempt to make your solar pool heater work better by slowing down water flowing through the panels. On the other hand, it is unnecessary to put more water through the panels than needed, which would just waste energy. The ideal scenario is to use a variable speed pump to “dial in” the optimum flow rate depending on the number of panels in your system. For example, if you have 8 panels, 32 gallons per minute might be ideal depending on the panel size, leaving a little extra flow to account for your filter getting dirty. Flow rates up to about 7 gallons per minute are fine for larger panels in the 4’x12′ range, but you get greatly diminishing returns from higher flow rates.

As you can see in the chart below for a FAFCO brand Sunsaver ™ solar pool heating panel, the panel reaches 80% efficiency with 4 GPM flow rate, and the curve really flattens out for flow rates above that.


Solar Pool Heating Panel Ideal Flow Rate


  1. Hi Jason. I was chatting with Susan and she said to ask you. Thanks so much for this article. I don’t understand ” if you have 8 panels, 32 gallons per minute would be ideal” Doesn’t the water flow from one panel to the next so that it would go about 30 gallons a minute through all? Or do you have a header that drops 4 gallons into each panel? Do you have a sketch or layout for how to use 5 of your glazed collectors?

    Also, I have my pool pump, but also a small solar pump – 2 Laing D5’s in series that can run all day long. Is there a way to have both running through the same panels so that when the stronger pump goes on it doesn’t force the others to run backwards into the pool? Perhaps a floating ball one way valve?

    1. Author


      Solar pool heating panels are arranged in a parallel configuration. It is essentially a z-configuration manifold. 32 gallons per minute of total system flow means you will have approximately 4 GPM flowing through each panel if properly balanced. Yes, each panel has an intake and discharge header. Solar pool heating uses unglazed collectors, not glazed collectors.

      Your DC solar pumps have nowhere near the flow rate required for effective solar pool heating performance. If run in parallel with your filtration pump they would be deadheaded with no flow. You could install a check valve to stop reverse flow, but again, the pumps would be deadheaded. There is no application for pumps this small in a solar pool heating environment. You need a lot more horsepower to generate the flow required for effective heating and the pressure required to close the vacuum relief valve. Even a higher horsepower solar pool pump (filtration pump) is not suitable due to the varying flow generated from such pumps.

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