Over the years, our office has received requests for design assistance for systems involving two hydronic heat sources, each in different buildings, where the expectation is to have either heat source supply heat to either building. One situation involved a mod/con boiler in a house along with a cordwood gasification boiler with thermal storage tank in a heated outbuilding located about 100 feet from the house. Both buildings had zoned slab type floor heating.
The owner wanted to use heat from the cordwood gasification boiler, when available, to heat the outbuilding and the house. The mod/con boiler would serve as the auxiliary heat source for both the house and the out building during times when the cordwood boiler was either off or unable to meet the load.