What is this & why is it there?

What is the build up in the funace & why is it there. It looks like wax. It is located at the right side of the picture. It was also on the line at the balancing damper located on the flue.

Also is the home made device in the supply duct to help push the air?



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I have no idea what it is, but I have found the same thing before. I didnt have to explain it as the furnace was toast.


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It looks like it is a booster fan for that duct. Sometimes HVAC companies will add these when there is a long run and clients complain that a room is not getting enough heat. A simple way to tell would be to activate the HVAC system and feel for a motor/fan running. Is that a rheostat or a switch? I bet its a rheostat.


Does this unit have electronic air filters by any chance? That almost looks like it could be for a sail switch that turns the filters on after the fan is up to speed. :shock:


This is what is called “temperature zoning” the duct has a damper that is controlled by thermostat that homeowner contolls.They might not want heat in a particular area and they program thermostat to open or close damper and divert heat or a/c elsewhere.

This is the short answer

I’m talking about the oozing, waxlike, silicone like substance.