I have a capped 3/4" pipe in a concrete slab meant to bring natural gas to an outdoor fireplace; however, I have lots of left-over 1/2" pipe & fittings from another project. Yeah, I might be "cheap," but wondering what effect would it be on a fire element if I were to install a 3/4" to 1/2" reducer and used my surplus piping?

  • Hello, and welcome to Home Improvement. It's impossible to say without knowing the expected gas usage, and probably hard even then. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Jun 27 '19 at 3:12
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    I have a natural gas outdoor fireplace (home made by me) and an indoor gas log set. Both run fine on 1/2" pipe, in fact the same 1/2" branch line tees off and supplies both. I don't run them simultaneously though... – Jimmy Fix-it Jun 27 '19 at 4:31

If you were going to pull a permit, you'd be required to submit a pipe sizing calculation. There are several methods of doing this, the Longest Length Method is very popular.

How to use the Longest Length Method


If you only have one then it should be fine.

There are ways to calculate the losses but you need to know several things like friction factor, Reynolds number ie laminar or turbulent flow and velocity which you don’t mention.

This is a link to an online calculator, and it also has some general friction factors. Bear in mind that losses accrue for bends and fittings as well as straight lengths of pipe.

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