Appreciate all your input. I'm not at all sure how I'm going to heat that area, Maybe a hot water Modine isn't a viable idea from what you all are saying. One of those less expensive forced hot air gasifiers that operate like the Kuuma line, rather than a boiler, might be a better solution. I'll have to look up what they cost and their build quality. I do have a 300(?) gallon propane tank nearby if I wanted to go that route. But I haven't spent a penny for fuel over the past five years with the Tarm Solo Innova in use, and would hate to start paying for fuel again. I 'm only thinking out loud here, maybe foolishly, about a possible way to cut building costs by utilizing the existing heating system to heat the shop.
Gencop, radiant would probably mean frozen pipes in the winter as I only anticipate using the shop intermittently.
Hedge wood, appreciate your idea of a hx with antifreeze, I hadn't thought of that.
Bad LP- I do heat my 3000 sq ft. home off that 1000 gallons storage, but am also concerned adding the load of 916 square feet, even for only intermittent heating, would overtax the system. Good point.
Brenndatomu, like hedge wood mentioned, they do make modines that work off hot water, although the ones you describe are probably more commonplace.
Mike