jebatty, Your radiant system is about the same as my situation right now. My homemade Garn principle boiler is setting in my repair shop, (40'x48'x12'H) and is radiating most of its heat into my shop. The tank is a 1500gal milk tank that has about 1300 gal. of water storage, minusing firebox and flues. I have been firing mine about every 36hrs. I fire at 135-140 and usually raise it to 190 with a smaller wheelbarrow full of wood that is not seasoned at all. When it gets up above 30*F and boiler above 150*F, its almost to warm to work in the shop without opening a window. I have future plans to install and insulate the boiler in a separate structure before next heating season.