I will install the Caddy on slab on grade, there will be no basement/crawl space. With correct design I hope the Caddy will do the job for an ICF passive solar house of 3600 sq.ft., with good insulation and windows. Instead of oil backup and/or additional oil furnace I prefer to go with the electric backup. I guess this is a safer approach for the Caddy, there will be one flue for the wood only. This will also save the space and the potential problems related to burning oil. If there will be not enogh heat I prefer to add a wood stove (I am serious about heating with wood ). Now, I undertsand that the key of success in using a wood furnace (or a furnace in general) is a good ductwork design. I'll have to learn this area also. Many thanks!