I have a 36' x 48' two story building. The bottom floor is a horse barn, with a concrete slab heated with in-floor heating. In the winter, the second story home is mostly unoccupied. We still like to heat the upstairs when unoccupied, at about 55 degrees (obvious reasons, cold winters in MT). My question is: Is it more cost effective to turn up the radiant floor in the barn and allow that to heat the upstairs, or keep the forced air system on, and heating the 2nd story? We generally leave the in-floor at about 47 degrees unless we are doing a lot of work inside. Boiler runs off propane. Thanks!

A great deal would depend on your insulation. If the floor is heated to 47, that heat rises and would keep the upstairs about the same if there is a passage way. You can lower the forced hot air down to 50 with no damage to the furnace of plumbing