New mod-con Indirect DHW heat transfer problem

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James Robins

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It was quite some time ago, but I do think there was a clip at the time of initial install. I have all manner of paper clips and other wedgies. In any event, that will be up to the installer to get right. The 43 gallons is enough, no doubt, but the question is how quickly the marginal thermal capacity of the double wall can recover at a paltry 23.5kBTU/hr. (based on 210F!) as opposed to 94.1kBTU for the single wall version.

UPDATE: Looking at the installation manuals of the single wall vs. double wall tanks, I see that only the SWs have an aquastat with a well behind it. The DW is a thermostat that appears to be essentially a surface mount. Presumably, these have an electronic sensor connection located within the tank. So, this is where the incompatibility comes in - with the boiler not able to accept the readings from the thermostatic sensor. Essentially, a surface area sensor (from the boiler) can't possibly get anywhere near sensing the water temp in the tank area because, of course, two walls with air between them are in the way! See install manual p 23-24 and 33 for the parts illustration -
Quite different from the single wall manual:

Having talked in the Spring to a couple of experts firmly opposed to double walls, I've learned that they actually are MORE prone to failure of those two paper-thin walls compared to the far-more durable single wall. In every possible way, the double wall is inferior... but they are so limited in production that they command a 50% cost premium! If I had known the pitfalls before jumping in, I'd have looked for an alternative solution. So much for energy efficiency, safety, or a basic understanding of physics...

It might come down to the cold return (Laing) vs. the SPE-1 circulator-pulse (Taco) options. I'm pretty strongly inclined toward the latter. Variable flow and better tank mix with warm water mixed from the bottom of the tank should yield better sensor performance up above, and longer tank life. Not to mention health concerns related to mixing water between hot and cold... especially so in a house that has mostly lead solder connections.
Hey, wait a minute.

This is awkward, but...

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