Solar Pool Heating on a Flat Roof

Solar Pool Heaters on Flat Roofs

In Education, Opinion Leave a Comment

Like many homes, yours may have a flat roof adjacent to your pool deck over a lanai or sitting area. This is a common architectural feature for Florida homes. It is often close to the pool equipment, you can’t see it, and it seems like it would be a suitable place to install a solar pool heater.

However, we do not recommend installing solar pool heating panels on flat roofs, and we refuse to do so except under very specific circumstances.

The reasons may not be so obvious, and most people think it’s about heating performance when we tell them. That is not really the case. A solar pool heating collector placed flat on a roof will have less heating performance than on a south pitched roof, but not dramatically in South Florida due to our latitude. Solar pool heaters are not as reliant on pitch as solar electric panels, and flat mounted panels perform acceptably (and great in summer).

The real reason we don’t install solar panels for pools on flat roofs is twofold:

  1. Solar panels mounted flat cannot drain fully.
  2. Flat roofs are particularly prone to leaks with fastener penetrations.
Solar Pool Heating on a Flat Roof

The flat roof on this home may seem suitable at first, but it’s not a good candidate for solar panels. Note the water stains from pooling water.

The Importance of Solar Panel Draining

The main reason that manufacturers require solar panels are installed to drain down when the pump goes off is that water in the panels can freeze, expand, and rupture tubes. This is not covered by warranties when panels are not installed and plumbed to drain. Believe it or not, a couple nights a year in South Florida when freezing temperature occur can cause irreparable devastation to solar pool heating panels if not drained.

But we have a second reason to drain panels that is fairly unique, even relative to northern and central parts of Florida. We go through a long summer period where pools are often too warm, and solar pool heaters are shut down during this time. Seasonal residents also shut down solar pool heaters when leaving for the summer. What happens on a flat roof is that water that can’t drain stagnates in the panels, getting very hot, and softens the plastics of the panels and adjacent plumbing to the extent that they swell, warp, and weaken. Some dealers don’t even isolate systems when shut off, causing pressure in the panels. Combined with stagnation, panels eventually weaken and burst.

While it is possible to manually drain panels on a flat roof, it requires a lot of laborious work, and it is pretty impractical. A slight pitch on a “flat roof” is not enough to fully drain a solar pool heating panel.

Flat Roof Leak Risks

There is only one correct way to install a solar pool heater on a roof in South Florida, and that involves penetrating through the outer roof membrane with fasteners to strongly attach solar panels to the roof structure to counteract wind uplift forces. This is the only way to meet building code requirements. Sadly, some dealers are content with using adhesives to glue down blocks to an asphaltic or membrane roof where the solar panels are then attached. If someone offers to install solar panels this way on your home, ask them to see the engineering that supports it. I’d love to see it (it doesn’t exist).

We won’t install solar panels in a way that does not meet Florida Building Code and the engineering that supports our installation method, along with the manufacturer’s installation instructions. That means roof penetrations with fasteners are required. On a pitched roof we have several products and methods that work together to ensure a watertight seal as water sheets around the anchors we use to attach solar panels. There is no such product for flat roofs.

Flat roofs, even those with a pitch, tend to pool up water in places. A pool of water around a fastened anchor, even one that is well sealed, can eventually result in a leak. Even worse, the anchors and fasteners themselves can dam up water, creating a potential leak point.

Finally, solar pool heating panels on flat roofs tend to move around more from expansion, contraction, and wind. This causes excess abrasion on the roof and can result in leaks in the panels or the roof.

Our Recommendation

If you have another suitable roof, even if it is not optimal, install your solar panels there instead of a flat roof. Your long term satisfaction with the product will be greater, and you will avoid the cost and aggravation of roof leaks. If you absolutely insist on a flat roof installation, we require strongly worded disclaimers and disclaim all responsibility for the results. Our warranty is also voided. You might also consider a traditional pool heater.

It’s all about educating our prospective clients and helping them make informed decisions. Even if we lose the opportunity to earn your business because of our policy, we hope you will heed our advice, and do not install a solar pool heater on a flat roof.

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