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Using solar to heat my pool

rt_2 Member Posts: 86
Hi guys,

I've got a 21' above ground pool and I'm thinking of trying to heat the water to lengthen the swimming season by using the sun. The hoses going to and from my pool are 1 1/2" dia. I'm thinking using 4 lengths of used hot water baseboard. The reason I'm going with 4 is that the area of four 3/4" baseboard pipes is the same as the area of my pump hoses. This way it shouldn't put any strain on my pump. I would build a manifold with a 1 1/2' inlet and reduced down to four 3/4" outlets and then feeding all four baseboards at the same time with another manifold at the other end of the heaters to go to the pool . Has anyone ever tried this. Should I paint all the fins a flat black? What else could I do to make it more efficient.  Thanks ahead of time.



  • SWEI
    SWEI Member Posts: 7,356
    oh, where to start?

    Forget about the baseboard - it's designed to couple 180F water to air and will be next to useless as a solar collector. You need square feet -- unglazed pool collectors are cheap and efficient.
  • rt_2
    rt_2 Member Posts: 86
    Really? You just bursted my bubble!!!!!

    I was just thinking that the fins would act as a heat sink and heat up then transfer the heat to the pipes and ultimately to the water. There's allot of square feet if you add up all square inches of all the fins.

  • SWEI
    SWEI Member Posts: 7,356
    square feet

    Maximum absorption happens when sunlight is perpendicular to the collector surface.  The more square feet of sunlight you intercept, the more heat you collect.  Besides being vertical and far too close together (how much sunlight actually falls on them?) those fins are optimized for heating air and will actually lose heat rather effectively.  Six feet of baseboard with six inch wide fins has 3 square feet of collector area.  Compare with ~32 square feet for a 4x8 flat plate.  The energy of sunlight is measured in Watts per square meter.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Rule of thumb..

    These are some older rules, so bear that in mind.

    If the collector is a glazed collector, you will need roughly half the exposed surface area of the pool in the way of solar collectors to extend the season by one month on either end.

    If unglazed, match the surface area of the exposed pool for the same effect.

    Unglazed collectors, as made by FAFCO, are relatively inexpensive, but if you're dead set on doing it yourself (DIY), then possibly consider doing a parallel configuration of PVC pipes, painted black, with an 1-1/2" header on one side, and 1" rungs, over to another 1-1/2" header. As SWEI pointed out, you need as much absorptive area as possible, preferably at a right angle to the incomings suns rays, hopefully within 15 degrees of dead South.

    The other "issue" you will have to address is how you control flow through the array. Normally done using a simple controller and a 3 way diverting valve, otherwise, if you go with a fixed bypass valve arrangement, you will lose at night what you gained during the day, and during the day, your pool might get so hot that it is un-useable at night. Neither of which are good scenarios.

    Have you considered a pool cover? A clear bubble cover can reduce the energy consumption by 50%, and can also give you a passive solar collector on top of your pool surface.

    I have seen people place coils of black PE tubing and use that as their collector. I have a friend who wants to hook up a bunch of green garden hoses in parallel, because he is familiar with how hot the water gets setting in a hose sitting in the sun... pressure drop be damned ;-)

    Don't forget to incorporate WInterization provisions into your design, or it may be trash next Spring.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • rt_2
    rt_2 Member Posts: 86

    Thanks guys for your help. That's why I called on the experts. You guys saved me a few bucks. I think I'll buy one already made. Has anyone out there tried the one's made by Game Model 4513? What they are is 66 feet of plastic pipe mounted on a dome and then encased in a clear plastic cover.It measures 33" X 33" and it's about 20" high. I have a 21 foot above ground pool and I'm wondering if one would heat my pool up here in New Hampshire. Thanks ahead of time.

  • hot_rod
    hot_rod Member Posts: 15,037
    the ambient air temperature

    has a lot to do with the performance of an unglazed collector. When the ambient is the same or close to the pool temperature they are very efficient 90% perhaps.

    This graph shows the comparison between 3 common collectors, notice across the bottom line the efficiency of the collectors as temperature drops 10, 20 and 30 degrees below ambient. So consider typical ambient to pool temperature in those months you are looking to extend.

    Unglazed collectors are great in warm climates like Florida and So Cal, maybe not so good in your climate? Consider shopping for some used glazed flat plate collectors if you want to extend the season in cooler outdoor temperatures.

    This link leads to a tech journal that explains how to use the graph to compare collectors, with data from the SRCC website on collectors.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jack
    Jack Member Posts: 1,045
    Mark's suggestion

    Of a well fit pool cover is critical. As the NH nights cool you could loose all and more you may have gained with your solar system.
  • rt_2
    rt_2 Member Posts: 86


    You said pool cover and I'm thinking you meant to say solar blanket. Is that right?

This discussion has been closed.