I have come across a 6" air chamber stub tee’d off of the hot water supply of the hot water tank, about 6" above the tank. Any reason in paticular? Just curios?
Any reason you think it’s more then just a hammer arrestor? My guess would be the last people had a problem with the pipes shaking when either the dishwasher or washing machine shut off and that was either the most convenient place to put it or the place where the shaking was the worst.
Sounds like an expansion tank. More info here:
The only expansion tanks I have any expiernce with are the ones for well water pumps I’ve seen on “Ask This Old House” but those are normally quite a bit larger then what the OP is describing.
The OP seems to be describing something like this from what I can tell. Would that be big enough for a water heater to push back against (based on that article…which I didn’t know was an issue)?
hammer arrestors work best near the valve being shut off so the shock is suppressed quickly. not to say there wouldn’t also be one in the hot water outlet of your water heater.
That doesn’t mean the person that installed it knew that. Especially if that’s where the pipes where rattling. Of course we haven’t heard back from the OP yet.
OTOH, it could be something entirely different. It’s could even just be a T with a cap that someone put when they changed the water heater. Maybe with plans of adding something else someday and this way they wouldn’t have to cut into the pipe again.
IANAP. During a plumbing project, I had no way to couple two copper pipes. I put in a “T” and capped a short stub of copper in the unnecessary arm of the “T”. It worked fine. Again, IANAP!
Please OP, more info.
The backflow preventers started becoming common on public water systems about 5 years ago and are now required in many places. I was active on a Q&A site then. Another old guy and I were puzzled about the rash of open pressure relief valves on hot water tanks. Took us a while to figure it out. Finally we realized the authorities were installing the backflow preventers without warning the homeowners to install expansion tanks or even telling them they did it.
As in the ask the builder link, the excess water has to go somewhere as it heats. In the past it went back out the supply line. With a well, it can continue to back up into the pressure tank.
This is also why without an expansion tank, any time you shut the water off, you need to open a hot water tap.
IANAP either, but…
The tee dead end (about 8" long? 8 inches above the tank?) on top of my hot water tank is where they put the saddle tap to feed the humidifier for my furnace. It’s a screw-on saddle that contains a drill in tap that then feeds a very thin copper pipe. I guess hot water evaporates faster, and you need a humidifier in the winter in Canada with hardwood floors.
Whether that was its purpose - probably not. It was installed with the tank before the humdifier was asked for. (And only 3 years ago) It can’t be to stop the pipes rattling, because 10 inches above this it turns into the flexible white plumbing hose material new construction uses. (metal flex inside PVC, I think). And - it’s horizontal, so it won’t trap any air to “soften the blow” when pipes turn off.
On older plumbing projects I did with hard pipe (copper, PVC, CPVC), I’d often leave a bunch of stubs around… A Tee, a piece of scrap, and a cap isn’t all that expensive, and it makes it worlds easier later if you need to modify or add lines somewhere.
Now with PEX and manifolds, I don’t bother anymore.