WNY wrote:unless there was a back draft damper in your ductwork to prevent reverse flow, you should hook it to the cold air side, and use your furance blower to SUCK the warm air from the Hyfire into your ductwork.
The built in blowers on the Hyfire are probably not powerful enough to overcome the resistance in your ductwork/filter.
What it's doing is the flow is going all over in your ductwork by trying to push it from the Hyfire, it's probalby going the wrong way into your cold air return ducts, that is why they recommend using the furnace blower to suck the heat and cold air the correct way thru the duct work.
Thanks Dave. I am going to give it a try now. I think you are right about the air going the wrong way from the cold air return. It is definetly not going into the furnace. I will let you know the verdict.