Insulation, Radiant and Vapor Barriers - insulate around ducting

When our kitchen was remodeled, the contractor put in new ducting from a down draft stove vent to the outsite of the house. This runs through a hole he cut in the subfloor and then along the underside of the crawl space, througha hole to the outside of the house. The problem is that the ducting is 4" or 5" but the hole he made in the subfloor is probably 7" or 8". This leaves a big gap around the ducting and cold air goes through this gap. When we stand in front of our stove we can feel the cold air blowing on our feet. I tried putting some excess insulation that is between the joists in the crawlspace into this gap around the ducting, but a lot of air still gets through. I am looking for ideas on how to insulate or block this air flow. Do I need to worry about the ducting getting hot since it carries the exhaust from the stove which can be pretty hot?

Thanks!

"Do not cover or pack insulation around bare stovepipes, flues, electrical fixtures, motors or any heat-producing equipment such as recessed lighting fixtures because trapped heat and blocked air circulation can create safety problems ("IC" rated recessed lighting fixtures can be insulated). Air leaks around flues and chimneys SHOULD be sealed using fire-resistant materials such as sheet metal and high temperature caulk.

Spray Foam: "DO NOT USE near flammable applications (e.g., flue vents)."

"Do It Yourself Home Sealing." EPA. Retrieved 27 May 2002. http://www.epa.gov/hhiptool/envelopedoyourself.html

I have a follow up question I guess...

The ducting that has the gap around it is for the downdraft fan which came as part of our stove. Is this still considered heat producing? It doesn't seem to get that hot...

The gap around the ducting is too big to use caulking alone. I was wondering what to use to fill in the gap. Looking at the link you mentioned, it really didn't say what to use in this situation.

Thanks!

They make metal escutcheons to go around vent pipes. Metal escutcheons are frequently seen around woodstove vent pipes and cover that gap where the pipe goes through the wall or ceiling. You could fashion one from metal to cover the gap where the duct goes into the floor.