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I am looking into building a patio with a fireplace. I'd like the fireplace to run off of my home's natural gas. When I built the house they ran a natural gas line from the furnace to a place that we could put it outside for a patio (about a 30 foot run). Now I'll need have someone run an additional 25 feet to the fireplace location on the patio. For a total of 55ish feet with a 1/2" pipe, my very basic understanding is that the pressure is going to be very very low and that I'll never be able to get a fireplace to output anywhere close to 150,000ish BTUs that I desire. Is it even worth me testing out the pressure of the current 30 foot run, or should I just move on and build something using propane tanks?

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You want a 150,000 BTU firepit? That's like a gas bonfire! Most gas fire pits I've seen are in the 30-50k BTU range, a few are 100k.

1/2" pipe run 55ft is good for about 70 cu. ft. / hour, assuming 2 PSI or less supply. At 1100 BTU per cu. ft., that will get you 77,000 BTUs, somewhere in the upper end of what I've seen for fire pits.

For 150,000 BTUs, you are going to need about 136 cu. ft. / hr so for 55ft you would need a 3/4" pipe, all the way back to your trunk line (I'm not counting your total demand on that trunk line)..

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  • Thanks, wow I didn't think I'd get anything near 70 cu ft./hr. It's a flexible pipe if that makes any difference. It's less of a firepit and more of a fireplace surrounded by three sides with a hearth and everything so I was thinking 150,000 might be right for that. Do you still think that's way overkill for a full fledged fireplace?
    – ShawnLane
    May 13, 2019 at 15:12
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With 1/2 lb gas it will not be possible to support the fire pit you have in mind with 1/2" pipe. You can either repipe clear back to the meter with the right size of pipe or use bottle gas.

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  • I think standard gas pressure is 7" WC or about 1/4 psi.
    – Jim Stewart
    May 11, 2019 at 0:28
  • Why is this answer different than J Raefield's? Is it because of the difference between a 1/2lb gas line and a 1/2" gas line?
    – ShawnLane
    May 13, 2019 at 15:14
  • The old standard was 7" water column in many areas, which equates to about 1/2 PSI (Pounds per Square Inch) of pressure. But starting a decade or so ago as more and more people started connecting to Natural Gas systems, the new standard now in many places is 2PSI. So it depends on where you are.
    – JRaef
    May 13, 2019 at 19:07
  • 1/2 inch has to do with the pipe inside diameter. Volume of gas (Cubic Feet per Minute or CFM) is a function of the pressure of the gas and the size of the pipe, along with the friction / turbulence created by turns in the pipe
    – JRaef
    May 13, 2019 at 19:43

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