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I have been challenged to design a circular fireplace as follows: approx. 6 foot diameter firepit with a metal hood for a vent. the installation will be in a lodge in South Dakota (for those of you living in the southern areas that means cold and windy). The location will be in a converted barn. My concerns are: #1 Will a fresh air supply be necessary to ensure that the draft will not pull all of the heated air from the structure? #2 What size for the hood in relation to the firepit? #3 What material to construct the flue pipe from to ensure a good draft and protect framing materials from the heat (the flue will need to be about 30 feet long). #4 Will there be any need for a power vent on the flue. and #5 Will there be a problem with smoke escaping into the room if the hood is 5-6 feet above the fire?
Obviously, this will only be used occasionally and not as a source of heat. If anyone out there has any ideas or suggestions I would appreciate the help. Thanks! Kevin Anderson.
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I can't answer all of these but here's my 2 cents -
1 - maybe. Design it in with a valve for control that can be shiut if unneccessary. This will also be effected if it is a room where it is likely that the doors and windows will often be open, like a ski lodge where folks are always coming and going.
2 - guess it should be about same diameter????
3 - Better draft in a typical chimney comes from masonry that , once heated, will help keep a steady draft happenning. I would try to find a solid mineral insulation filled metal pipe in a copper colouror get matealasbestos and clad it yourself. the weight would need to be suspended with wire. Plain metal pipe would need to be 18" from combustables (check with local codes on that)
4 - Very likely so! This was my first thought. The volumn of air available to the pit vs the volumn of CFH carried by the pipe is extremely unbalanced. Fireplaces like this are notorius for smoking because of inadequate draft. This same connects to #5
5 - As the hood gets higher, the possiblity of losing draft increases. The shape of the hood is important too. a tall dome or inverted cone will start air flow into the chimney better than a flat lid.
It might be necessary to use a glass surrond and control airflow via the intake vent #1. I'm sure this is not the theme you want.
*I'd bring a fresh air supply in to the bottom of the firepit from beneath the floor.The normal design is for the firebed to be about 18" above the floor level and the start of the hood to be about 2'6" above the firebed.I would suggest the hood be at least large enough to cover the firebed.The shape of the hood should be as Piffin suggests and a damper in the flue so it can be closed when not in use is also a good idea.
*"4 - Very likely so" Would use "Probably" or "Yes" if anything except gas "logs"Tried this once (actually a 6 ft triangle on one wall, and was for heat rather than just ambience). 28 ft 18" dia flue in reinforced slipformed concrete chimney. Hood was only 30" above hearth, tapering to point at 10 ft ceiling (flue off the side at 8 ft height). Smoked badly until everything hot, still smoked occasionally after that. Did not try forced draft, but that is what coal power plants use.Finally ended up with tempered glass surround, ditched that for steel doors with animal shapes outline cuts after finding what a pain it was to keep glass clean.
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I have been challenged to design a circular fireplace as follows: approx. 6 foot diameter firepit with a metal hood for a vent. the installation will be in a lodge in South Dakota (for those of you living in the southern areas that means cold and windy). The location will be in a converted barn. My concerns are: #1 Will a fresh air supply be necessary to ensure that the draft will not pull all of the heated air from the structure? #2 What size for the hood in relation to the firepit? #3 What material to construct the flue pipe from to ensure a good draft and protect framing materials from the heat (the flue will need to be about 30 feet long). #4 Will there be any need for a power vent on the flue. and #5 Will there be a problem with smoke escaping into the room if the hood is 5-6 feet above the fire?
Obviously, this will only be used occasionally and not as a source of heat. If anyone out there has any ideas or suggestions I would appreciate the help. Thanks! Kevin Anderson.