Delta T
I wish I did not buy this unit. A $5. Timer to the circulator pump is all you need. On cloudy days, a common light sencer that turns on the power when the sun hits it activates the circulator pump. If your water temp get over 190 Degrees, temp sensor clamped to the hot output of the tank will break the circuit to the circulator. This sensor is $15 and is the size of a large watch battery with 2 electrical spades connections on it. This way of doing it stops the circulator pump running unnecessarily.
I will say, going solar hot water is awesome. I never run out of hot water and it saves me over 75% on my hot water fuel bill. Plus I have 18 feet of base board in the basement plumbed to the return feed to the roof panels. That free heat eliminated the musty smell in the basement.
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