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Jason - You mentioned in a post above, on Feb 24, 2007, that you didn't know where the rumors about using salt to clean chimneys come from... Well, the "rumor" probably starts in places like this...


... the full text of a guidelines for chimney construction from the National Board of Fire Underwriters Committee on the Construction of Buildings. Several major building and design professional organizations contributed to its writing and it was recommended for state law adoption, much in the way "model" building codes are written today. See the Appendix, section "VIII" toward the end of document for a recommendation by the U.S. Fuel Administration recommending salt as a chimney and boiler flue cleaning agent.

Don't know if using salt is the current "best practice", but fires, chimneys, salt and chimney sweeps have all been around a long time, and all precede the writing of this model code by decades if not centuries. So, I would assume there was some historical evidence that using salt, indeed, works or it wouldn't have found its way into such a document.

Jason Raddenbach

TH, I see now where the rumor is coming from, but is there any science behind the suggestion in the code? I have long ago learned that something is not necessarily true (or a good idea) just because “professionals” included it in their code.

Burning standard table salt NaCl would produce a sodium and chlorine gas only at 800C or ~1400F. No furnace or fireplace could reach that temp, only a kiln could. But taking flame to salt creates an intense yellow color because of the flame hitting the sodium metal. Perhaps this “fireworks” display gives the illusion of a chemical separation taking place. Ah, so maybe the truth is it is all a slight of hand trick!? I would love to hear the science one way or another.

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