Englander Wood Furnace - tying into existing HVAC duct

First time poster, long time reader...

After much research I just bougth a
Englander
Model # 28-3500
3,000 sq. ft. Wood-Burning Add-On Furnace

From Home Depot (site to store) - it should be here in the next week or so.

I am just sketching out the "plumbing", I have an existing wood stove which exhausts into a masonry flu, I think that will be easy to work with, but the question is how to tie into the existing heating duct work.

The existing stove is in the basement at one side of the house the main (heat pump / electric) HVAC is in the center of the house. I have a HVAC "feed" which I could tie in easily from the Englander, but I am worried that it might not feed the entire house.

So the question is am I better "directly" tying into the end of the trunk line near the Englander, or should I run 8" solid metal pipe all the way back to the main feed point of the exiting HVAC system? I assume it would be better to insulate this pipe as the run might be 25 ft total leading to the existing trunk.

So what is better having a "short" 10 ft run and tying into the end of the trunk or running all the way back to the main split of the trunk near the existing HVAC system?

THANKS IN ADVANCE!

I was plannning / have on order a backdraft damper: http://www.homedepot.com/p/Speedi-P...8+in.+Galvanized+Back+Draft+Prevention+Damper

This is suggested per the mfg to prevent the normal HVAC from feeding back into the Englander.

Also, the Englander only has one 8" pipe to tie in; I know most others have two, but this unit is physically smaller and only has one.

Thanks!