That looks like a steal for $640. I seen a hand fired forced air stove on eBay go for around $1,000 recently.
In the owners manual coaledsweat refers too there are great diagrams on how to tie your coal furnace into your existing duct work. Anyone interested in ideas on how to tie in coal furnaces into existing hot air furnaces take a peek at their model 1400 pdf towards the back.
This season I started burning, I am using a standard coal burner that I tied into the duct work with my existing gas furnace. It works, but it’s not like something engineered to do the job. I’d love to have the big blower and controls that puppy has. Stove envy.
If your unit has the two 8inch takeoffs like some of the US Stoves, into one 10 inch, I can see your concern. The 10 inch main duct might be fine for this season, but you should have a little closer to 16 inchs of main trunk. I’ve read that HVAC practice that has you neck down your trunk as it goes. So if you started at 16 (maybe rectangle duct), ran a few feet then 12, a few more feet then 10 you keep the same pressure. You might not need to replace your entire 10 foot run if you research this principal and it applies to you.
I recommend two things for a new coal hot air beginner.
#1. A digital temperature gauge, with an external probe for the outside temperature. Look for one that shows 10ths, so you can see it say 88.6, 88.7, 88.8. Put the outside probe in your duct work. Be careful the probe doesn’t touch the duct itself, otherwise it will read a lower temperature from the metal. You’ll know for sure what you’re blowing after the combustion fan kicks off. Circulating air isn’t always a bad thing, even if its just 80 degree air, it will keep your house at a more even temperature. 80-85 degree air doesn’t feel that warm out of the registers, but it could keeps your house warm when it’s in to 40s and 50s outside. I read one some of the US Stoves have a 1 speed fans with 2 or 3 speed fans as an option. It’s possible yours is a one speed, with the controls for variable speed. Maybe you can email them part numbers of what you have.
#2. A draft gauge or more officially known as a manometer is a big help. A good draft is critical for a coal fire, and if you can keep it steady and controllable you will have less problems and a more efficient furnace. If you have a barometric damper great, that takes a lot of the guess work out... and you might be fine without. Anyway, you plumb a manometer in your chimney pipe between your stove and your damper. I did mine while I was still burning… just be careful and wear gloves. Dwyer makes a great one for $31.75 + tax and sh of a few bucks. http://www.dwyer-inst.com/htdocs/pressure/Model25-40Price.cfm
The Mark II Model 25 is in the range we need. -0.04 to -0.06 is most typical.
Good luck, and send some pictures