Gas Line Sizing

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thillaj

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Hi -

Can I do this??? I am replacing a gas water heater with a tankliess one that can demand up to 199,000 BTU. The existing gas line branch that serves the water heater & gas dryer is 1/2" black pipe 15 feet in length. This branch is the first one teed off the 1 1/4" main at 20 feet from meter. The tankless water heater requires 3/4" service. Can I just use a 1/2" to 3/4" adapter at the tee and replace the branch line with 3/4" pipe??? Would that pass code??? Or must I really replace the 1 1/4" X 1 1/4" X 1/2" tee with a 1 1/4" X 1 1/4" X 3/4" tee???

Thanx
 
I have

I have done exactly that with Rinnai water heaters and they work fine, I just jumped up to 3/4" right away. Some of those installations have been in several years with no issues. I'd say do it.
 
The 3/4" pipe will support 200,000 BTU for about 20' or so, depending on how muc pressure drop you can tolerate. The fitting probably will not drop a lot, but I think I would run a pressure test after you install it to be sure that the WH still has adequate gas pressure at its inlet even under max load. Any problems with gas pressure will cause erratic operation.
 
Pass code¿

That's awesome that you're pulling a permit and getting this work inspected by the county/city. :)
 
Thanx!!!

Guys, I've got the baby installed & it's working great!!!! The 1/2" to 3/4" adapter was sure time-saving. Thanks for the advice.

Only part I have I have to re-visit is putting a condensate drain in the horizontal section of the vertical venting stack. Rheem insists that it must be done, else water condensate will flow back into the burner. How much water vapor could there be generated anyway???
 
I think at this point it's too late. The gas work being done under a permit must be inspected before being put into service. Although it would not hurt to at the very least pay a plumber to perform a thorough leak check and code compliancy of said unit.
 
Codes & Permits

Everything I've done is exposed. I believe I've done everything to code (that's why I come here when I'm not sure). I am perfectly capable of running a leak test before starting it up (which I did). The condensate drain is not readily available so that's why I skipped it. I have ordered it from Rheem & will redo the horizontal exhaust section to include it.
 
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