American Harvest secondary furnace add-on install

[boroak]

Hello, I am new to pellet stoves/ furnaces and I have an American harvest 6100/6500. According to the manual for them you only need one back flow damper if you plug it in as a second furnace and want to use the existing duct-work. It doesn't seem to make a lot of sense to me, when some furnaces call for two dampers. Just looking for an opinion here but should we add a way to cut the air off to our oil furnace so that the air doesn't flow into that and only through the supply for the ducts?
Thank you for any tips or help.

 

[Jeremy6500]

Hello, I am new to pellet stoves/ furnaces and I have an American harvest 6100/6500. According to the manual for them you only need one back flow damper if you plug it in as a second furnace and want to use the existing duct-work. It doesn't seem to make a lot of sense to me, when some furnaces call for two dampers. Just looking for an opinion here but should we add a way to cut the air off to our oil furnace so that the air doesn't flow into that and only through the supply for the ducts?
Thank you for any tips or help.

View attachment 310745

The damper is for when you are running the furnace and not the stove (or AC in the summer). It keep the hot/cold air coming out of the furnace from taking the easy/short loop back down the stove supply, through the stove and into furnace return through the shared return. Without is you would lose a lot of furnace flow out your room vents and it would kill efficiency.

If you were wanting to run the stove and not the furnace you would need a damper somewhere in the furnace track to keep the same from happening with it. This is the situation I will end up in because when all is said and done I will have an air handler with an AC/Heat pump coil that is a separate unit than the stove, but will share a return.