any of the foams are going to be much more expensive for the same r value. also depending on the temperature you're going to run the tank at you may need to go polyiso as the others melt at a lot closer to solar hot water temps.
Since my tank will be in ground foam was the only option. I think I could get away with any of the foamboards but I found used polyiso on for real cheap and bought a bunch.
Last edited by strider3700; 09-22-11 at 12:24 PM..
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