Does the red valve on right-most pipe control the water flowing into the water heater? The water heater needs to be replaced, so if the valve is closed to drain the old water heater, it would be good to know which direction the water is flowing.

enter image description here

  • 1
    run hot water in a sink ... one pipe will get very warm and the other will remain cold
    – jsotola
    Mar 26, 2022 at 19:12

2 Answers 2


Many tanks have "hot"/"cold" or "in"/"out" subtly indicated on top or the valves may have arrows to indicate the intended flow direction.

If you look closely, you'll see "COLD" stamped into the metal, next to the pipe, on the right side of the picture--the side with the valve.

marking on water inlet

  • Well, we see " C O " which we can assume is the start of C O L D. Mar 26, 2022 at 4:46
  • 1
    "subtly" LOL. Pretty clear indicator... Mar 26, 2022 at 12:32

The installation manual for a Rheem 40-Gal water heater shows this drawing on page 6, which superficially looks very similar to your photo:
enter image description here

It shows the incoming cold supply on the right and outgoing hot on the left.
What could confirm this for you (if the water heater still works) is if you run hot water for a short time and test the temperature of the pipes - you should easily be able to tell the difference between them.

Another way to confirm whether or not that valve controls the inlet or the outlet would be to raise the lever on the T&P Relief Valve on the top, then turn the wall valve off. I'm assuming that the T&P outlet pipe runs somewhere "safe" which won't cause trouble if it gets wet...

If the water stops flowing through the relief valve (or even slows down significantly) then the wall valve is on the incoming cold supply.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.