Multiple Boiler Setup

JPSheat

HI... Im looking for suggestions on the most efficient way to combine 2 boilers in a heating project im working on.. Here on the general specs.

The boilers need to heat the house(radiant heat)  DHW (12 GPM)  and a hot tub.   The primary boiler will be coal fired and the secondary will be oil fired.  Each of the boilers are adequate to satisfy the complete household load individually.. however the main  reason for the back up is for vacations when the coal stoker will not be able to be fed..

Do I want to connect the boilers in parallel  keeping both hot all the time using just one primary pump and one expansion tank .  Or set them up independently so either one can work when the other one is cold and off. using a series of valves to switch from oil to coal and visa versa. Any creative solutions would be helpful..

thanks

furnacefigher15

I assume both boilers are indoors

Pipe them in parallel with valve one supply and return of both. If you want the off boiler to stay warm, then crack the valves open allowing for a slow flow of warm water.



Note any flow though the off boiler will represent a thermal loss, and typically a significant one.



So for optimum efficiency, the off boiler would have no flow. But when change over is needed crack the valves open and let the running boiler pre heat the off boiler prior to turning on the burner,