Our water heater has two valves located on extended pipes perpendicular to the hot and cold water lines. When Spring hit, the maintenance people in my complex mentioned we needed to turn the valves before the AC would run properly (we tried running the AC first and it was producing no cold air). Since these aren't connected at all to the actual AC unit, as far as I can see, I'm confused about what they do and whether or not I should turn them back off if I want to switch back to heat.

Mystery valves on water heater

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    Actually they are off as pictured in the photo. Turn them again now, it won't effect your AC.
    – Tyson
    May 17, 2016 at 15:22
  • Can you sketch out any plumbing connections that your A/C has to your plumbing?
    – Freiheit
    May 17, 2016 at 18:18
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    The 4.5" dia. galvanized pipe standing on little legs extending vertically from the water heater is called the flue pipe and during heater operation is filled with hot gas. I mention this as a reference point so that when I tell you that the maintenance people in your complex are full of hot gas, you have something to compare them to. May 17, 2016 at 18:25

1 Answer 1


Answer to Question asked originally

That appears to be unused piping that goes nowhere now. The valves were shutoffs for whatever was that direction. The pipes appear to be capped now, meaning the valves have no function now.

Answer to question as Edited

These pipes and valves still have no purpose. Take the picture you posted to your maintenance people that told you to turn the valves and ask for clarification. FWIW, the valves as shown are turned off.

Additional Guessing and Theories

If your AC uses water it's likely an Evaporative Cooler (sometimes called a Swamp Cooler--typically found in dry/arid climates). In that case, the AC would take a supply line to fill, but not a return line. If in fact turning a valve on solved your problem it was a different valve and not either of the two shown.

It's also possible that your AC unit's supply water supply isn't your water. It's only a guess, but maybe your neighbor (you said apartment) got similar advice to turn on a valve and their valve feeds both units.

In any case my advise above still stands, show the maintenance man the picture you've shown us and ask for clarification about WHICH valve is associated with the air conditioning.

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    What else did you try to fix the AC? These valves have nothing to do with your AC working.
    – Tyson
    May 17, 2016 at 14:58
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    They obviously do nothing. Google the post hoc fallacy if you're bored. :) My guess is that they were future-proofing. It's not uncommon for plumbers, especially in commercial situations, to set up for additional circuits that may be needed down the road.
    – isherwood
    May 17, 2016 at 15:12
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    Considering the location, my guess is some kind of recirculation pump that's been removed. As Tyson says, nothing at all to do with the AC.
    – BMitch
    May 17, 2016 at 16:05
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    I got clarification, they are in fact defunct, they used to be part of a system that used hot water for heating but it was replaced recently. The AC working sporadically turned out to be because the A-coil was completely clogged and the lines were freezing periodically, so it was just a coincidence that they were un-frozen the day we turned the valves.
    – thanby
    Jun 4, 2016 at 16:17

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