Ducting an add on furnace

[saichele]

I'm contemplating adding a wood add on furnace, and I've got the chimney side under control.

My issue is in the ductwork. The chimney thimble is about 40 ft across the basement from the furnace, and I'm not excited about running duct all over the place, chewing up headroom. But the house system (a basic ranch footprint) is set up such that there are two main runs, a supply and a return, down the long axis of the house, and they happen to terminate right by the chimney which would be terribly convenient.

How much difference would there be between tapping the supply and return at the furnace plenum, compared to hooking up to the other end of the main trunk?

Thanks
Steve.

 

[STIHLY DAN]

Ductwork tends to get smaller as the trunk gets longer to keep up the static pressure. If yours does this then it is not a good thing.

 

[saichele]

Nope - two long box ducts running down the long axis of the house, and 6" round lines coming off to the various registers and returns. I don't anticipate reducting the house - at least the stuff that's there is all taped and insulated.

 

[STIHLY DAN]

Sounds like your good to go, as long as your area clearances are met.