I understand the duct loss, but why is it hard on your furnace? Say you heated the room the furnace was in to 80* and used the cold air return to move it around the house via the furnace. Am I following this correctly?
The heat coming out of ducting connecting to my pellet stove is 150 Deg F!
It is not hard on the furnace. The heat going into the cold air return from the pellet burner keeps the furnace from coming on. That is exactly how wood pellet furnaces are connected into the house!
See the US Stove 8500 pellet furnace Add on Installation page 11 - I am a US Stove Dealer and I have serviced this setup.
(broken link removed to http://www.sylvane.com/media/documents/products/usstove-8500-multi-fuel-furnace-owner's-manual.pdf)
When installed as a secondary furnace, it may only be connected to the ductwork of the existing primary furnace (Gas,
Electric, etc.). It should not be wired in conjunction with the existing furnace’s circuitry. A Duct Damper must be installed
between the air discharge of the 8500 furnace and the primary furnace. This duct damper prevents the air of the primary
furnace from back flowing to the secondary furnace. The damper must be a mechanical (spring return) style with
a simple closure switch to determine if the damper is opened or closed. The damper will connect to the 8500’s printed
circuit board (PCB) as a signal connection only. See wiring diagram in this manual. The PCB will not supply power to
an electronic damper requiring a power supply. This power supply must come from a different source.
CAUTION: Do not connect your furnace’s ductwork to the cold air return duct of your existing furnace because a possibility
exists of components of the central furnace overheating and causing it to operate other than intended. Only connect
to ductwork that is in good condition. Never direct the air flow from the exisiting furnace thru the Add-On furnace.