I will be venting my electric clothes dryer through a pre-cut hole in the floor. It will be vented using flexible, foil type tubing and traveling a short distance to an exhaust on the side of my home. My concern is how hot the dryer venting may get that is almost touching the bare wood hole in the floor. I haven't found a collar that would fit around the 4 inch tubing and fit the hole, which is around 5 inches. Could I line the hole with a silver foil duct tape used for HVAC jobs, etc. to protect it against the heat? Suggestions?
It's not a concern. Dryer exhaust might hit 200 degrees, but most have thermal fuses far below that. You'd need twice that and then some to start a fire. Heck, many dryers are vented through cheap vinyl hose. If it was a concern building codes would require double-wall flues akin to those used for gas appliance exhaust.
I do recommend against the lightweight foil hose, though. It really accumulates lint. Use semi-rigid aluminum pipe at least (example). Its ridges are much smaller and it's less likely to close up on itself in a bend.
You may have heard of the risk of not cleaning the lint filter. This can result in reduced airflow and heat accumulation, but any fire is likely to begin in the dryer in this case. More on that