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I'm building a large screen porch. The roof is held up by wooden trusses and there is no ceiling. There will be ceiling fans attached to the joists on the trusses (but they won't be run when we have a fire in the fire pit). I'm planning a chimney on the ridgeline of the roof. (The fire pit may be off center, but I figure if the chimney is on the ridge, then the smoke will rise and always find its way up to the chimney.)

I'm thinking about putting a wood burning firepit on the porch. If I do that, how high would the bottom of the roof trusses have to be to be fire-safe? (Note I'm not worried about discoloration.)

Also, what if I switched to a propane fire pit?


This is not the same as this question. The variations may be slight, but the other question is in enough of a different setting that the answers there didn't give me the answers I needed.

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    There is no "safe" height. Don't do this. Aug 30, 2019 at 5:47
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    This is a variation on diy.stackexchange.com/questions/127205/…
    – DaveM
    Aug 30, 2019 at 12:13
  • 1000 feet should do. (Don't do this--you can't catch all the sparks that almost certainly will void your insurance claim.)
    – isherwood
    Aug 30, 2019 at 13:37
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    Without a hood and vent through the roof this would not be allowed. Going through the roof next to the framework you will need a reduced clearance box (we used to call them zero clearance ceiling boxes) because an uninsulated pipe requires 18” from combustible materials I think triple lined or class A can go down to 2 “ clearance.
    – Ed Beal
    Aug 30, 2019 at 14:13
  • Does your house have a mortgage on it? Does the mortage require you keep insurance on the property? (Yes) What does your fire insurance say about this scheme? Aug 31, 2019 at 3:44

1 Answer 1

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Every place I've lived has city or state laws that prohibit this. In Virginia, the law says no open fires (exludes bonfire which is 50') within 25' of a structure.. So, don't do this.

If you are intent on continuing anyway, sketchy, unproven advice can be read below...

Ten feet clearance above the flame would be needed. Wood fires can reach over 2000 F (bonfires) and more typically are a bit over 1000 F in normal fire pit use; wood's flash point is at 572 F.

You can greatly mitigate the clearance by using things like a metal hood (think stove top hood, but bigger) or even a metal sheet dropped below the trusses several inches for airflow. I don't know of any exact designs for this, but you can probably simulate this fairly easily with a piece of paper on a large metal sheet over the fire; if the paper catches fire (451 F flash point) within 4 hours, it would be too close.

However, the bigger problem is the smoke. It will be an issue in a semi-enclosed space. I think a hood can greatly help, but the reality is that gas fireplaces are used in these scenarios as the temperature is quite a bit lower and it burns clean. This is the proper solution to your problem.

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  • The second link suggests a 10-foot clearance around the fire, not above it. Other sources I've read suggest at least a 20-foot clearance for tree branches above a fire pit, so you'll need even more than that for a solid structure that you don't want to damage. Aug 30, 2019 at 13:48
  • With a chimney on the roof, won't the smoke rise up into the rafters and to the highest point (ridge line) and go up through the chimney? And will there be the same problems with a propane fire pit?
    – Tango
    Aug 30, 2019 at 16:42
  • @Tango The chimney would need to go through the roof to properly ventilate. And no, propane/gas fireplaces do not need the same amount of ventilation. One brand I just looked at today for this answer only needed a 5' clearance. Aug 30, 2019 at 16:45
  • I'm rephrasing, to be sure I understand. So if the chimney goes through the roof at the ridgeline, it would ventilate? And you're saying a propane fire is different enough it's not an issue?
    – Tango
    Aug 30, 2019 at 17:05
  • @Tango So long as the chimney goes through the roof and extends up a bit, I don't see why it matters if it is at the ridge line. Propane/gas burn so much cleaner than wood that smoke is not an issue and they are more controlled in temperature; think about a gas grill, they normally only get 500-600 F. Aug 30, 2019 at 17:08

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