My old house has those black plastic covered flexible "pipes" to take the central air from the units in the cellar to the converted upstairs bedrooms. They wind around between the original lath/plaster ceiling and a dropped ceiling, as do copper water pipes for the upstairs bathroom. I noticed a major "hot spot" in a room and upon inspection found it corrolates to the hole in the ceiling where the flex pipe goes to the second floor, so I assume I have a major air leak! My question is... can I put expanding foam around the hole to seal it from the attic air (hot in summer/cold in winter)? Any problems with this? Any specifications? THANKS!