It would be brand new. From what I've read from others they aren't that inefficient. Obviously I would never believe the 73% or whatever it is that the company claims, but I would be happy as long as it isn't burning through 15-20 cord like the traditional owbs are known to do
"From what you read"???
Again, if you are going to ask for advice, you have to consider that we've been through 30+ years of installing and selling these things - and we have real engineers here who use real equipment to take real efficiency measurements....
I'm not stating how much wood you are going to go through - but that some OWB's and "old" technology boilers will be lucky to hit 30% total system efficiency. That's the way it is. A properly designed higher efficiency system could hit double that.
Maybe you will burn 12 cords instead of 6, 10 instead of 5 or 7.......but you will burn a lot more and create a lot more smoke and pollution.