I have an electric forced air furnace, located in my garage. Garage is insulated, but not heated. The furnace used to have foil faced insulation on it, noticed it was extremely dusty when I bumped into it the other day. Also seems to be pretty dusty inside the house. Couple questions... 1) Should I seal the joints with the proper foil tape? Or are these joints already airtight? 2) What should I use to replace the insulation on it? There's a gap between the sheet metal and the floor where it used to be stuffed underneath. Can I use rigid polystyrene or will it be too hot? 3) Where the ducting enters the ceiling, can see a bunch of batt insulation sort of sticking out (can sort of see it in the second picture). What would be a good way to seal that off? If I change the oil in a vehicle in the garage, we can smell it upstairs even if the furnace isn't on. Sort of thinking the fumes are travelling through there? Thanks!