You may have heard me say before not to use any type of rubber when insulating the pipes of solar hot water systems. The picture to the right shows why. This rubber insulation was installed on a new A/C unit only some 4 years ago. The unit is in the shadow of a building and is as protected from the weather as any outside unit can be. There are no extreme temperatures involved here.
Many commercial and residential solar installers use Armaflex and Rubatex foam insulation on solar thermal systems. There are several grades, including one for outdoor use. This material typically won’t last long on a solar water heating system out in the sun with high pipe temperatures. Some contractors have used latex paint to protect the rubber surface. As far as I’ve seen, that may add a year to the life of the rubber. Eventually it will deteriorate and need replacing.
The best way to protect the external piping of a solar hot water system is to use an aluminum jacketing over either fiberglass or iso foam insulation. The jacket must be carefully installed to prevent moisture penetration. This is done by “shingling” or lapping the joints downhill. Seams should be on the bottom. As an added layer of protection, I always recommend caulking the seams and joints.
The butt joint between the aluminum jacket and the collectors – and the small lines between collectors – are the hardest to seal. A big bead of silicone caulk at the joint is required. This spot is the most prone to shrinking and pulling apart, so it should be checked periodically.
Doing things right the first time may take a little more time and cost a little more money. But installing a solar thermal system that will pass the tests of time and exposure are well worth it to the owner.
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