Clayton 7.1

Nothing but problems with this furnace. Ok the furnace is about 30 years old out of my parents basement. It was used about 2 winters then never used again. It sat for all those years.So I took it out for my greenhouse heat. I have the unit sitting outside under it's own shelter. The cold air return is with flex duct work and about a 3' run. The hot air outlet is again with insulated 12" flex duct work. about 10' of flex the over to 10' of metal.

Now here is my problem, the furnace is making my allergies go nuts. My throat gets dry and sore, nose runs like crazy and I sneeze like you cannot believe. Now this is the 2nd year with the greenhouse , last I had a wood stove inside there and all the plant are the same. I know it's not the plants.

I removed all of the insulation from the flex duct on the inside of the greenhouse. I checked all of the flex duct for holes or loose insulation. The inside shell of the furnace has insulation with a foil backing facing the stove or where the cool air passes over. I broke down the top outlet the other day and could not see any loose insulation. I even put the leaf blower down inside to see if anything would come out, nothing. Now without a dust mask I can't go in. Any ideas? Should I remove the furnace shell and remove all of the insulation?

No soil or anything moving around, I did put a cold air return air filter in

No rodents. All venting is clean. No rodent calling cards