[Greenbuilding] air sealing a metal fireplace flue

[RT]

On Tue, 21 Jan 2014 12:20:21 -0500, Alan Abrams
<alan at abramsdesignbuild.com> wrote:


>  air sealing the flue.

> manufacturer, states that a two inch clearance must be maintained around
> the 6" ID / 8" OD double wall flue pipe.
> given the primary air barrier is the roof sheathing itself, the most
> reasonable sounding option seems to be a sheet metal flange, cut to fit  
> the elliptical section where the pipe penetrates the sheathing with a  
> gap of
> maybe 1/4", and caulk it with some high temp pookie.  the sheet metal can
> then be sealed to the sheathing with some of Ken Levenson's best sticky
> tape.
>
> this would still leave the individual joints in the piping


The stainless steel insulated chimney that I installed in my own home has  
2-inch thick walls (7 inch inside diameter, 11 inch outside diameter)  
required that a two inch clearance be maintained between it and insulation  
or framing.

I started the insulated chimney at the ceiling of the first floor level so  
it runs through a double-height second storey conditioned interior space  
before penetrating the interior air barrier at the second storey ceiling  
and entering the roof insulation/framing cavity.

Rather than have the chimney penetrate the A/B through an elliptical hole  
in a sloped ceiling, the penetration point was changed to a horizontal  
plane so that a smaller, round penetration (ie easier to ensure a good  
fit) would be required.

A sheet metal flange with a hole cut 3/4 inch smaller in diameter than the  
O/D of the chimney was used.
The edges of the hole were then peened over to create a "turtleneck"  
collar to fit nicely around the chimney and provide a pocket for a ring of  
silicon firestop caulking .


5 inch wide sheet metal collars (ie same width as auxiliary support  
brackets) were installed over the joints between chimney sections, two  
bolts on either side of the joint. The collars not only helped to seal the  
joints between the chimney sections, they beefed up the joints helping to  
make the relatively tall chimney assembly more rigid.

-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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