ivE built a shed/greenhouse, deer stand, around my central boiler, the entire boiler is on the warm side except for the door. Its a greenhouse on the warm side also, and while im working on it i have hooked up a small woodstove that taps into the outdoor wood boiler chimney clean out door. I almost have a secondary heating loop off the boiler finished. Originally, i put a magic heat in the chimney in efforts to use pure waste heat to heat the greenhouse, but the corrosive massive amounts of creasote ate up the magic heat. that was a stupid idea anyway.
The greenhouse is not very airtight yet, but residual heat and some solor heat raised the temperature in there today, before I started the woodstove. Today 32 degrees in the room, before i started small woodstove, in there while it was 15 degrees outside.
I do know that my outdoor boiler has less than three inches of foam at the access panel, and this is not really that much.
obviously, its probably not worth it to construct a building around the OWB purely for efficiency sake, but if you need a small heated space, or want a greenhouse/workshop anyway, it seems to make sense. This small building does have a small second floor attic, that allows me to access the chimney and run a brush down it once in a while...
I will post picturs of it later.
barkeatr