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djmc 10-04-2012 11:02 AM

Outdoor Masonry Fireplace Chimney/Flue = Help?
I'm having an outdoor wood-burning fireplace built. The fireplace opening is 43" W x 31" H, although the width dimension tapers back to about 34" W at the back of the firebox. The gentleman who constructed it did not slant the back or build a smoke shelf and chamber, etc. Rather, he used 8"x8" concrete block to create a vertical smoke pipe in the center of the firebox "ceiling" that is approximately 43" tall. I have read both negative and positive about such direct-vertical smoke pipes, but undertand the pipe/flue may need to be taller. Anyway, I am wondering how tall the smoke pipe should be?

I have a relatively new metal gas-water heater vent pipe with vent-pipe cap I can utilize to insert into the concrete-block smoke pipe. Will that work and benefit my system? The size of that metal pipe would allow me to extend the flue/chimney several feet.

Any advice is much appreciated.

pwgsx 10-05-2012 03:02 PM

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When i built my outdoor fireplace I discovered the chimney would have to be 10ft + to vent correctly and I was not about to do that in my backyard. I had smoke pouring out the front , it was horrible. I ended up building a metal smoke shelf from metal sheet and adding a blower vent to pull the smoke out. Works great now.

jomama45 10-07-2012 08:14 PM

The flue is sized off of the front opening generally, but it's a little different "ballgame" when it comes to exterior FP's. If anything, they should be built to the same strict, proven standards and dimensions as an interior FP, minus the clearances to combustables and they don't need outside air or a damper. They tend to be much more fussy than interior FP's when it comes to smoking out o the front, and as such, generally require a larger flue size to compensate for it, when compared to the interior equivalent. W/O looking at a chart, I'd say you'd want at least a 12" x 16" flue for that size opening, or a minimum of 130 sq. inches of actual opening. More would be better though, and 180-200 is probably much safer. Highly unlikely you have a flue pipe that big laying around though......

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