Questions about ducting an englander furnace

[2broke2ride]

So I am very seriously considering purchasing an englander add on furnace to replace my main wood stove. That being said, I have no ductwork in the house as it is currently a baseboard hot water setup so I would be starting from scratch. I have seen mention here of minimum clearances to combustibles for the ductwork, what are these clearances? I asked a local HVAC company owner who has his trucks serviced at my shop and he said he has never heard of minimum clearances for duct work. Also, isn't this supposed to be an add on to existing ductwork so the same clearance or lack of in the existing ductwork shod be fine for this no? I read the owners manual online cover to cover and see no mention of this.
Some of my ducts would have to run between a floor and a drywall ceiling in the finished portion of the basement so clearance is a premium.
I am planning to run a rectangular trunk line equivalent to the 8" round outlet on the furnace and then have 5 or 6 branches off the trunk......... What size branch lines would I use and how many can I get away with with the 850cfm. Blower?

Thanks
Kevin

 

[maple1]

Don't want to utilize the existing hot water baseboard?

 

[2broke2ride]

Unfortunately a wood boiler is way out of the budget.......... I figure I can do the englander for around $2k including ductwork and that's a high estimate.

 

[1970roadrunner]

Minimum clearance to combustibles for the ductwork is common, but is specific to the particular unit. I would suggest calling Englander and asking about it.