I have a 1986 95% efficiency Hotpoint furnace and want to improve the efficiency by trapping as much heat as I can in the Ducts. I’ve wrapped the initial Duct coming out of the Furnace with reflectix but when the furnace is on, it is still too hot to touch. Is there a special Duct that belongs next to the furnace so the outside feels cool? I feel this will improve the efficiency by not radiating the heat into the garage through the duct.( and then I can wrap it )