Subject: Re: Fireplace creosote deposition - Interior fireplace

From: [email-masked] (Nick Pine)
Date: 14 Apr 1995 04:01:47 -0400

[email-masked] (Will Stewart) writes:
 
>   I plan to use an interior fireplace to avoid having a cold masonry flue  
>   exposure. The top of the chimney will be insulated to reduce heat loss.  
>   Are there any formulas or rules of thumbs for these conditions?
>
>   At what temperature (or delta T) does deposition take place?  

Perhaps you could use two concentric fluepipes, or three for leak-safety
(Norman Saunder's suggestion), with the flue gas going up thru the center one
(made from 316 stainless steel?) and outside air coming down from the roof
between the outer ones, to make a counterflow air-air heat exchanger that
would work even when there is no fire. Unlike typical triple-walled fluepipe,
there would be no insulation in this assembly, or perhaps some thermal shunts,
eg bolts, thru the insulation. If the joints nest downwards, w/o horizontal
sections, the creosote, condensation, etc. in the flue gas should end up back
in the fireplace, regardless of the (ideally low) exit temperature.

The fireplace might be enclosed and airtight, to be more efficient.
Part of the air that comes down from the roof might be combustion air. 

Nick