Re: SB: Fireplace in Bale Wall

[Norbert Senf <mheat@mha-net.org>]

At 12:41 AM 2001-06-20 -0400, Speireag Alden wrote:

>     I remember past posts on the chemical changes which happen in 
> cellulose materials subject to persistent heat, and the past experience 
> of one poster who had a chimney fire because of faulty design where there 
> was no air space.

Hi Speireag:

The UL (Underwriters' Laboratories) requirement is that the combustibles 
can't get more than 90deg F above ambient for an enclosed air space or 117 
deg F above ambient for a vented air space. Otherwise, you get pyrolysis of 
the cellulose, which lowers its ignition point over time.


>     Still, it's clear that you can't have a total air space, or there 
> would be a four-inch gap between the fire place and the wall through 
> which you could see daylight.  Thermally questionable at best.
>
>     So, how do you bridge that necessary four-inch gap?  Can you insulate 
> it at all?  Doesn't it constitute a break in the thermal envelope?  I'm 
> unclear on the details, clearly.  What exactly butts up against the chimbley?

Best solution - put the fireplace inside the house. The conventional 
outside wall fireplace penetrating the thermal envelope with an outside 
chimney is a foolish idea intended to save some floor space, and results in 
poor fireplace performance.

If you put it on an outside wall, you can use non combustible constuction 
for that part of the wall. Non combustible construction is metal studs with 
fiberglass or Roxul insulation, and cement board instead of drywall. Also, 
the hot area is immediately behind the firebox. Further out on the ends, 
things are cooler, and you could have short wing walls to enclose the air 
space.

Believe it or not, there are no good details for this in conventional 
construction - most tract houses these days simply use a framed chase and 
pop in a cheap "builders box" sheet metal zero clearance fireplace, usually 
with gas logs. Tack on some fake stone and an expensive mantle, and away 
you go.

Best ....... Norbert


----------------------------------------
Norbert Senf---------- mheat@mha-net.org-nospam
Masonry Stove Builders	(remove -nospam)
RR 5, Shawville------- www.heatkit.com		
Quebec J0X 2Y0-------- fax:-----819.647.6082
---------------------- voice:---819.647.5092
			
		
				



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