[Greenbuilding] Fireplace questions

[Corwyn]

On Nov 08, 2006, at 10:43, Keith Winston wrote:
> It seems to me there's still a hot debate about the outside air issue.
> Often, the point is made that the fire must warm indoor or outdoor air
> to the same temperature before combustion, and therefor the net energy
> is the same.
>
> I wonder if that misses the point?

Depends on what point people are making, of course.

> As the fire burns, in the absence of
> an outside air feed it depressurizes the house somewhat, and fresh air
> is drawn in through whatever cracks and crevices can be found (which
> might include a cracked window or other explicit "air intakes"). There
> are a couple questions I have about this. Shouldn't the operator be
> adjusting that window, and finally closing it, as the fire dies out?

Couldn't this also be said of an outside air system.  There is usually 
no way shutting those off except by the normal fireplace controls.  
And, how well insulated are they?

> That's unlikely to happen reliably with most operators, and the window
> or cracks will be a source of heat loss until closed. If the fireplace
> has glass doors and the air feed is inside the firebox, then this can
> either be more easily ignored (net heat loss will be much less) or
> thermostatically controlled.

Why?

> Second, in this first case cold air is
> streaming in from one or more points, through the living space. The 
> very
> definition of drafty. If the house is too tight, then there are chances
> for backdrafting and introduction of combustion byproducts into the 
> space.

The back-drafting issue is, as you say, contested.  The only data I 
have seen showed no difference.  A decent fire is only drawing a few 
CFMs, I would feel hard pressed to notice it.  Drafty would, I think, 
be in the 100s of CFMs (more like my kitchen vent fan).

Thank You Kindly,

Corwyn


-- 
Corwyn
Kermit didn't know the half of it...
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