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How To

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Water Trap Primer

What's a water-trap you ask? Wikipedia provides a description along with drawings and photos but it might be a bit confusing if you try to apply this information to the Water Heater Installation project on the DirtyShirt website.

If you've landed on this page by some other means than viewing the Water Heater Installation project you might want to take a trip to the project and learn exactly why the unintentional creation of a water-trap caused the city to fail the installation due to the presence of a trap.

When referring specifically to plumbing, water-traps are very useful solutions within plumbing configurations; they are generally used to keep sewage gases from entering a dwelling and are intentionally configured within the plumbing of every building.

water trap

A water trap is a low spot relative to the input and output sides of the plumbing. In the illustration above the water heater pressure valve is the input side, the pressure valve plumbing is the output and the dip in the middle is where the water trap was formed with flexible braided stainless steel line.

The problem is that water heaters aren't connected to sewer lines so that's one reason you don't want or need a water-trap. The city is worried that if the pressure valve activates, water will just sit in the dip and/or create a plug, possibly creating pressure and causing a list of potential problems.

That all sounds logical on paper but how many times have you ever seen or heard of a water heater pressure relief valve actually activating? Never, right? We've not seen or heard of it either and the way Jeff configured the installation should have been fine – but sometimes it's just easier to get along and go along. All complaining aside, fixing it to meet code is the right thing to do to prevent future problems or it wouldn't be a code compliance issue in the first place.

water trap

Here's another complication: The water heater pressure relief valve and the wall plumbing are on the same plane as indicated by the horizontal red bar in the illustration above. The pressure valve is slightly higher – so how do you get the water to travel in a downward direction after you've added connecting hardware and flexible line?

Tear a hole in the wall and move the plumbing of course. In Water Heater Installation Video 2 Jeff talks about all of the reasons to tear a hole in an otherwise perfectly good wall:

  • There's no insulation in the wall.
  • As mentioned, we needed to move the pressure valve plumbing.
  • The plumbing in the wall isn't strapped down and the power cable isn't tied down to a stud either.
water trap

Here's what success looks like in the illustration above – a code compliant water heater installation.

Click to go to the DirtyShirt Water Heater Installation project.