When installing new natural gas plumbing system, can I include multiple capped tees for future branches?
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. &quot;Different&quot; isn't &quot;bad.&quot;
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&quot;. 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&quot;.
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 &quot;for free&quot; to which you could attach something later. In particular, the &quot;something&quot; 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.