Solar Pool Heaters for Flat Roofs

Solar Pool Heaters for Flat Roofs


Solar pool heating works great on flat roofs. You don’t need to build a structure to face the solar panels right at the sun. The cost of the structure is more than the cost of the solar panel in this case and we don’t want to have to bolt a structure to the roof. If its a really expensive solar panel made of glass or grown from a silicon crystal then sure, it makes sense to spend money on a structure to point it at the sun better but here we’re low tech. We’re low cost. Besides, flat on the roof means not exposed directly to the cooling effect of wind. We’re using the roof itself as the structure and the insulation on the back of the collector. Flat also means its not visible from ground level. Flexible Powerstrips can be walked on.

Powerstrips are fully repairable. You can splice them with 1/4" OD PVC drip irrigation tubing from the local hardware store using our special adhesive. The Powerstrip rigid header pipe is a styrene blend. It is co-incidentally compatible with pvc cements. You can’t do things like this with a polypropylene solar panel.

Don�t screw things into a flat roof. Water will pool and eventually find its way through the roofing membrane and you will be liable for damage to the home. Water can creep in for years and result in mold before any water appears inside the actual home. Solar heaters need to be installed in a way that does not affect the integrity of the flat roof membrane.

Flexible collectors have always been the standard for flat roof installations because flexibility means water can be trapped inside over winter with no freeze damage. The collector expands to accommodate the expanding water as it freezes. Conventional rigid collectors are lightweight sails that must be strapped and bolted down rendering them impractical.

Until Powerstrip came along, the problem with flexible collectors was compatibility with chlorine. Regular epdm synthetic rubber solar collectors will break down in chlorinated water. Hot Sun went to the extra trouble of developing a system using a thermo-plastic based material that has no chemistry issues with swimming pool water whatsoever.

Mounting the collectors securely on a flat roof was always an issue as well. Glue down, strap down, weight down residential methods did not stand up to the scrutiny of engineers and owners looking to approve a commercial installation. Hot Sun is proud to present our unique ballasted framework for mounting flexible Powerstrip solar collectors. Warning. This system does not work for other solar collectors brands. Only Powerstrip is flexible thermo-plastic so it can be secured to the framework at both ends. Rubber will pull too hard and affect the integrity of the framework. Rigid plastic will break if secured at both ends.

This system has been certified by professional engineers to withstand wind lift and seismic shift in standard non-hurricane zones. This manual addendum illustrates the specifics of the ballasted flat roof system in detail.

Watch the following video

The challenge with all solar heaters of all types is how to interface them with the roof. We’ve tried many different techniques over our 28 year history. The lesson we learned in the first week of our 28 years is that its not a good idea to bolt things through a flat roof. What we settled on after many trials and tribulations is a system that uses ballast to hold a framework of pipe to the roof. The Powerstrips are lashed to this framework of pipe. We designed it with commercial installations in mind but it turned out to be so inexpensive and so easy to put together with locally available materials that we started using it as our standard technique even for residential systems. Variations of it have been structurally and seismically certified for use in normal wind zones (not hurricane zones).

To hurricane rate a system like this we have no choice but to bolt and or in some cases glue the system to the roof. On some commercial applications this is simple because the roof surface is concrete.


In the case of gravel ballasted or tar and gravel roofs we can use the gravel itself as the ballast. In the example below we captured the existing gravel with a screen and tied the solar framework through the gravel to the screen. We’re using existing roof ballast as the ballast for the solar system.

To work up some pricing what we need you to do is first figure out how many sq ft your solar heater should be. Go though the sizing calculation or call us (858-683 0800 in US, 778 300 1803 in Canada) or e-mail with this information. You’ll also need to measure the roof (safely from ground level) so you know what can be fitted. With flat roofs we can often measure on Google Earth.


Powerstrips are 11.25" wide but the header pipes use up 13.5" each so that is the space needed for a 1 foot wide section. The strips can be as long as 88 feet. The ballast needs to occur every 10 Powerstrip sections and it is 8" wide so you need to allow for this space. Ten feet from the header pipes you’ll use a cross bar. Glue strip holds the collector tubing in place. These are spaced every 6 feet. The glue strip goes under the collector and is glued to the collector and secured to the framework at its ends.

Take a look at the summary installation manual addendum for ballasted flat roof installations .

To pack more Powerstrip into less space you can stagger the headers. In this case you don’t allow for the 13.5" header length. Instead you allow for the 11.25" width of a nominal one foot wide Powerstrip section.

Please e-mail Hot Sun or call us at 858 683 0800 or fill in the form and we’ll price this all out for you.


Large scale solar heaters are often configured on flat roofs because that is the space that is available.


We do have dealers that can install this for you in most markets. Call us for a referral but we’d like to answer your tough questions first, direct from the horse’s mouth. We also cater to do it yourselfers and independent contractors. The work itself is simple and well documented in this web site and with additonal detail depending on the specific circumstance. The real consideration is the risk of working on a roof. Even a flat roof is a dangerous work space. Anyone working at height needs to have fall safe protection training and certification.


On a flat roof installation we’re often going to winterize the system rather than risk piping or header pipe failures due to water expanding and bursting rigid plumbing. A very effective way to get all the water out very easily is with a shop vac. You just connect the hose of the shop vac to a removable coupling practically anywhere in the system and open the panel bank up at the opposite end and blast the air through (don’t vacuum, blow instead). Its quite surprizing how effective this technique is. Its also amazing how well the system heats the high flow of air once the water is all gone. Solar pool heating technology will become solar air heating technology if the markets for alternative energy ever materialize. This video shows the procedure.


POOLS is a detailed explanation of pressure and how we can set solar up to avoid unnecessary excess collector pressure. The following video is also very good but don’t try to become a solar engineer if you don’t have to. With new laws in California and greater awareness of the fact energy costs money on the part of the pool industry we’re heading back the good old days when pools pumps were never larger than 3/4HP for residential pools. If that’s the case then solar is a simple tie in Figure 1a of our main installation manual .

The best way to determine the right mechancial system design (the way solar is married to your pool system) is through consultation with us. We’ll either help reduce the pressure by solving pool mechanical issues (like an oversized pool pump that is costing you too much in electricity) or we’ll see if there is a way to regulate the pressure to the collectors. If you’re ready to go down this road please gather the information asked for at the top of the sizing page and as suggested there, fill in this form

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