I'm getting natural gas service installed and am plumbing in the system. Initially, the only appliance will be a gas water heater. I want to run the mainline and future-proof for new appliance installation later on (e.g. furnace, fireplace, range, etc).

Is there any issue with, during the initial install of the mainline, including several tee fittings stubbed out for future branches to where these appliances will probably be located? Specifically, I need to know if this would be a code violation and/or if the inspector would think me crazy.

Is there a better, more professional, or appropriate way to leave stubbed out ends for future installs?

Code should be in context of my locale: Snohomish County, Washington State, USA.

REF: WA State Residential Code (adopts IRC 2015)

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    IF you go this route, I'd suggest putting a shut off valve before each capped end. That way you can install each one with the valve closed, then when you're ready to attach something to that branch, you simply double check that the valve is off and remove the cap - no shutting off gas to the whole house to install (or later repair/replace) that one new appliance.
    – FreeMan
    Aug 4, 2020 at 18:04
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    Our house built 1970 has a tee pointing upward with a short length of pipe and a cap. This was presumably to allow easy addition of gas line for a gas range. I doubt that code would allow installation of a valve in the attic. Aug 4, 2020 at 22:12
  • @FreeMan since the initial branches will be off the mainline (running through the attic), that's where the tees will be located. Does it make sense to have all these shutoffs up in the attic? My plan was to (obviously) just have the shutoffs located before each appliance, where each shutoff would be accessible near the appliance itself for safety/maintenance concerns. Aug 5, 2020 at 23:01
  • Having the valves at the appliance does make a lot more sense than having the valves in the attic. I don't know what code says about having them in the attic, but, of course, that would be the ruling decision. I was wasn't expecting them to be that high!
    – FreeMan
    Aug 6, 2020 at 0:18
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    The original suggestion that valves be placed past the trees (presumably with a capped short pipe on the output side) was so that if a spur were later being added to serve a new appliance then the gas to the whole house would not have to be shut off. I assumed that there would be another valve located outside the wall by the appliance and the valve in the attic would be left permanently in the open position. Still a valve is a weak point and I doubted that the code would allow a valve in the attic. Aug 6, 2020 at 1:51

1 Answer 1


Having extra tees in place will stand out as uncommon but it's not inherently a code violation nor crazy. Inspectors may easily identify differences in workmanship between seasoned professionals and DIY/newbie/apprentices but don't worry about that. "Different" isn't "bad."

One thing you would need to do is oversize the pipe you do install now: having extra ports for addition of future loads is no good if the main pipe isn't sized adequately to support those loads. Knowing nothing about the appliances you have in mind nor the pipe length involved, but having gone through the pipe sizing exercise several times, I can suggest you're most likely going to want that main pipe to be 1". If high-demand appliances like a tankless water heater or large furnace are in the future, or if you find the difference in materials cost to be insignificant, you might choose to use 1-1/4".

An alternative to having a DIY manifold of capped tees is to install a tee where an elbow would ordinarily be used. That gives you a threaded port "for free" to which you could attach something later. In particular, the "something" that gets added later could include another tee so that again there's a spare port for later. The practicality of this depends on the layout of the room and the piping. I mention it only to point out that you may not need to add several tees now -- having just one tee now and remembering to add more later is functionally equal.

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    Make sure you check with the locals before you hook up any gas appliances. Many have laws against DIY'er hooking up those appliances. Many gas companies will do it for free and also check all your connections.
    – JACK
    Aug 4, 2020 at 17:53
  • Thanks for the answer, I really appreciate the perspective and feedback! I drafted a system design that includes capacity for pretty much all future appliances I'll want to install (by BTU consumption) plus a little extra. I've scheduled for a 1-1/4" gas service and matching M425 meter to be installed, so main line will be 1-1/4" running the half-length of the house where appliances will be. Then I plan to branch off with smaller pipes and possibly CSST (with required certification). So I should be set in terms of gas capacity and flow/pressure. Aug 5, 2020 at 22:56
  • @JACK thanks for the comment, I appreciate it! I don't see any code violations with gas appliance hookup, as long as a permit is pulled and inspector approves. Can you reference or point to an example to the contrary? Aug 5, 2020 at 23:03
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    @JakeHassings I just know it's a common warning on most gas appliances to check local codes and ordinances to ensure homeowner installation is permitted.
    – JACK
    Aug 5, 2020 at 23:19

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