safely insulating around hot vent pipes
Hi,
I have two vent pipes exiting through the wall of my utility room–one is a standard 4″ galvanized round venting a gas dryer, the other is a stainless 4″ round venting a propane-fired tankless hot water heater (Takagi T-KD20). What’s the safe way to insulate the wall cavity around these pipes? For the time being I’ve cleared away all sheetrock, poly, and insulation within about three inches of the vents, but would like to minimize cold air infiltration. This is an extremely well-insulated home in a cold New England climate.
Some details:
Walls are 7″ deep filled with blown-in-fiberglass (BIBS system)
water heater pipe attaches to a special stainless steel vent box (about 12″x12″x4″) that’s supplied by the manufacturer (there’s a photo at http://www.takagi-usa.com/web2003/c06.htm, middle of top row).
I assume the fiberglass insulation is flammable and so should not contact the pipes. What’s a good fireproof insulation material I could use there? What’s the standard practice for insulating around hot sidewall vent pipes?
Replies
Single wall vents on gas water heaters need 6" cleance from any combustible materials.
_______________________
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
Is the 6 inches code for water heaters?
So nothing but air can be surrounding the pipe in the wall cavity? Seems like there must be some fire-resistant material that you could use, but maybe not--I'm certainly no expert on this point.
And what does code say about dryer vents?
6 inch for single wall flue, 1" for double wall b-vent (those are for gas fired appliances.)
I'm not aware of any clearnace requirements for gas dryers, though. (Do not use plastic vent materail, however, it is NOT rated for use on dryers.)
FWIW, my gas dryer exhaust (after about 6' of metal vent) is 140 degrees F, my gas water heater flue gases uynder the bonnet are over 350 degrees.
Keep in mind that wood (and, perhaps, wood composite materials) undergo a process called pyrolysis - each time a piece of wood is heated, it's ignition temperature comes down slightly, so you can have a piece of wood too close to a flue for years with no problem and then have it ignite.
_______________________
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
On my woodstove and a few other hard to insulate items, I caulked the penetration of the exterior thimble and the pipe. Either furnace cement or high-temp automotive silicone as appropriate. Also caulked the framing inside the wall and the interior thimble. Nothing you can do about the air gaps. You can't fill them with anything. But, I checked with the woodstove people and the heater manufacturers and they said it was safe to caulk and eliminate air inflitration. If you don't have an interior metal thimble for the dryer, I'd make one, also frame a box to keep wall insulation at the proper clearance. At least you can keep air from flowing around the pipe. I wouldn't worry much about not having a square foot of insulation here and there. Probably a less heat loss than a window. Unless the manufacturer says you can pack insulation around the pipe, don't. I don't know about a dryer vent, but for most heaters and woodstoves it is not allowed.
I am not aware of any clearance requirements for dryer vents. They do not get very hot. If the wall vent were hot enough to support combustion, your clothes would have melted a long time ago. I suppose you could have a lint fire.