I'm heating a 4000 sq ft, 2 story colonial with no problems with my Koker. I love this thing! I believe the convection blower is rated at 1450 CFM. You'll have no problems pushing air through your existing duct work.
I "plumbed" in a fresh air supply for my combusion fan last weekend---I'm looking forward to improvements with this new supply of oxygen rich air for the combustion fan.
FYI: You'll probably need to throttle the stoker back with the square footage you're heating. I don't believe you'll need the Koker's full 160K BTU output!
Good choice! Hope you have a good supply of rice coal. I'm burning Blaschak bagged rice. I hope to score a ton of deep mined rice while I'm in NEPA for Thanksgiving.
BTW: Did you get the "thermostat" model? I added a digital programmable thermostat to my unit; and, this is now one slick set up for "sticking it to the man." The "energy" man of course... My 500 gallon propane tank is currently full. I plan to keep it that way all winter...
Enjoy Your Koker! It's a great machine!!