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Posted By Eureka,
Oct 3, 2018 at 11:16 PM
And I don't think you need that second exp tank by the HX.
Yes, how the flow switches are playing with the temperature regulation of the gas boiler is a bit of a fuzzy thing, in my mind at least. I would think the gas wouldn't fire if the boiler was hot enough even with flow through it? I have no experience with a gas boiler though.
I would also likely change my marked up version and put the DHW mixer after the boiler - so the boiler is getting the hottest water, to help prevent it from firing. And, since the DHW plate would be acting more or less as an on demand heater - I would also likely make it bigger.
I'm kind of thinking there might be two controlling things going on inside the boiler - one for heating & one for DHW? They might at times each have different temperature requirements also - DHW needing hotter stuff than in-floor but more infrequent. Kind of guessing at some of this.
But another consideration is that DHW demand is only a fraction of heating demand. Everyones situation is different of course but I think I see at our house that DHW demand is about 1/30 of heating demand, in the heating season. In other words - it might not really matter a whole lot if the gas still heats the DHW.
The manufacturer told me that the boiler will still fire with preheated water, and will error out. Too smart for its own good kind of thing.. High return temps (over a 20 degree difference) won’t allow it to operate normally. Which is the first thing I found out in all of this remember. I can’t heat the return water.
My household uses a lot of hot water, and I also will be using it for power washing.
Just put it there to keep positive pressure before the circulator. I’ve been told it’s a good practice and a good spot to have an air vent.