DPST Aquastat

Jim K in PA

I am designing a control system for my combination wood furnace (GARN gassifier with integral storage) and oil fired hydronic furnace as backup. I am pretty sure I need a DPST A-stat that will power a second in-line A-stat when the supply water from the wood furnace is above the oil burner cut in threshold. The second in-line A-stat will control the primary and secondary circ pumps. If the wood furnace goes cold, I want the in-boiler A-stat to remove power from in-line A-stat controlling the primary and secondary pumps and have the oil furnace fire and heat the zones. That way I do not throw heat into the oil burner/wood burner HX, wasting energy trying to heat up 2k gallons of water with the oil burner.

My existing A-stat is the standard Honeywell unit (sorry - do not ahve the # handy) on the temp well in the DHW coil plate. I need to replace that one with the DPST. Then I may use that OEM SPST A-stat on the inline well.

How does one go about mounting a temp well and A-stat on a 1.25" pipe? Suggestions for particular hardware is appreciated.

Thanks.

Jim