I have my furnace exhaust coming up from the basement to my attic.
Currently the B-vent comes into my attic floor from the second floor
ceiling with a good-sized triangular cutout around it, sorta like this,
looking from the top:
(If you aren't viewing in a fixed font, this won't make sense,
picture a triangle with a circle inside)
/ ___ \\
/ / \\ \\
/ ; ; \\
/ \\___/ \\
A significant draft comes out this triangle into my unheated attic.
I'd like to seal it up but am unsure how to proceed.
If memory serves, no flammable material can be within 1" of a B-vent.
So, could any nonflammable insulation be used to cover the hole and
butt up against the pipe? Are there any other issues?
Make something out of sheet metal, I was given an insulation piece by a
fireplace repairman that looked like fiberglass for inside my fireplace
in a crack, check a fireplace store to use it to fill the gap.
I'm a newcomer to this group but I am impressed with the rapid
responses and quality of information passed along.
I, too have a problem with my stove. It's a double-wall pipe and
cold air is leaking into my hom from the pipe. I've checked the draft
and it closes compleyely so I know its not coming in through the stove.
I believe the air space between the two walls of the pipe is where
the cold air is coming from. When I checked the pipe at the end of the
summer I could see some light as I looked down into the pipe. I figured
some of the insulation was missing and I was afraid I'd have a tough
time finding the right type. I'll try to find the rockwool ASAP.
There are a number of fire retardant or resistant materials. Vermiculite is
fireproof and can be filled in voids around a flue pipe. It is a little hard
to find though, at least in small quantities. The Schundler co. from NJ is a
major distributor and can help you to find some in your area
Max, your B vent is not correctly installed. It is *required* to have a metal
firestop where the vent pipe passes through each floor or ceiling. The
firestop is a flat piece of sheet metal with a hole cut out for the pipe, and a
clamp to hold it around the pipe. The sheetmetal is nailed to the floor or
Of course it has to be slid over the pipe as it is installed, but you could
probably get the correct size firestop and use snips to cut from the outside to
the center whole and twist the whole thing around the pipe to get it in place.
Here is a link to one brand, scroll down the page to see several different
styles. You can find them at Home Depot. The diameter of B vent is about 1/2"
larger than the nominal size, ie.e, if your pipe is 5 1/2" in outside diameter,
it is a 5" B vent (they go by inside diameter).
You are correct about the 1" clearance.
While I can't recommend using unfaced fiberglass insulation to insulate this
area, I will tell you that unfaced fiberglass insulation will not burn if
held in contact with direct flame. What you do with that information is up
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