Interested in a little more clarification/detail on this.
So, you have a "regular" forced air system, but you also have a pellet stove that can compliment (or fully heat) the system as well?
That's a really great idea.
Do both systems share the same heat transfer box (not sure if my terminology is correct) or do they operate more independently and the plumbing is just connected?
Do you have to manually control any ducting changes when you go from one to the other, or is it automated (or not necessary)?
basically what i have is a regular forced air system with a propane furnace and I also have a corn/pellet furnace with supply and return duct connections.
the pellet furnace supply duct connects to the main system supply duct and at that point i have a 24 volt damper so that i can separate the two systems when needed, that duct (the pellet furnace supply) also has a tee with a 24v damper that allows the pellet furnaces air to be dumped into the basement when the propane furnace is running. the dampers are controlled by a relay that is activated by the eac spade on the propane furnaces control board.
it basically tells the relay that the propane furnace is running and to switch the position of the dampers.(dump damper open and system damper shut)
this allows you to set the propane furnace stat on a desired setting and run the pellet furnace and if the pellet furnace isn't keeping up the propane furnace will come on and the pellet furnace will dump its air in the basement (which is still in the house) until the propane furnace is satisfied.
this is how i run mine, the propane furnace is set to 69 deg and will come on if the pellet furnace doesn't keep the house at least 69.
its worked well for me, this is my 6 year with this setup. its nice to have a backup heat source like 4 years ago when my propane furnace took a **** at

time. i just used the pellet furnace for a couple of weeks until i had time to change out the furnace.
also the pellet furnace has its own separate return duct connected a return grille in my dinning roomwall