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Single Thermostat, Two Heat Sources
I wanted ot bounce an idea off the collective experience here. We are installing a Propane Furnace with AC System in a new construction home with a hot water wood coil from a outdoor wood boiler.
I’m using a Taco 501 switching relay turn on the pump and close R and G for the furnace fan call. Wood boiler loop goes to a nearby hydronic separator and boiler pump runs continuously.
I wanted to use a single thermostat. My idea was to use a strap on adjustable aquastat set at maybe 150F on the boiler supply at the separator. The NC contacts allow a heat call to go to W1 on the furnace. NO contact to W on the switching relay. The swooned benefit is if water temp drops too low, it’s provides boiler protection and prevents cool air from blowing and furnace automatically picks up.
Also boiler is oversized, so this would allow the owner to add some storage, load up just enough wood for the load and storage capacity, and the propane picks up once he runs out of heat automatically.
Seemed like a simple and cheap solution and avoids having two thermostats on the wall.
Any thoughts or a better solution.
THnaks to the heatinghelp community for the separator idea/design. Should make purging dramatically easier and solves several issues and avoid two pumps in series. Boiler is 300’ away (sigh) on 1” PEX, but that’s enough heat. Only need 60-70k peak anyway.