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The current setup in my basement has a long pvc pipe going from the HVAC system to a floor drain about 8 feet away. When I had a new water heater installed the plumbers put in a drain pan underneath it but didn't set it up to actually drain anywhere.

I would like to try and hook the water heater's overpressure relief valve into the existing long pipe that's serving as my HVACs condensate drain line so that in the event it triggers and dumps the heater's contents it will flow into the floor drain instead of the drain pan. I got the idea after watching the same plumbers install my water softener and cut into the condensate line to hook up the softener's runoff hose.

Here is an overview of the pvc pipe going from the HVAC system on the left and disappearing into the wall to the floor drain on the right.

Overview of the condensate drain line

About halfway down the pvc pipe is the water heater pressure relief line that I want to tie in. Circled in red.

The water heater relief valve next to the condensate line

Here is how they hooked in the water softener.

How the water softener hooks into the condensate line

This is what the floor drain looks like in the other room. If you look back at the first picture you can see the pipe take a 90 degree turn at the end. This goes through some drywall and ends about 2 feet later over the drain. While I'm messing around with everything I'd like to enclose this if possible. I've been having humidity issues in the room and I suspect the open drain is part of the problem.

The floor drain

Here is my proposed plan to tie everything in. I was originally going to go with simple straight lines, but after reading this post I think I might need to leave the p-trap in. I'm not sure of the best way to connect the water heater into this, but I'm leaning towards a flexible hose like how the water softener is tied in. I want to have as much of a slope as possible going from the HVAC system to the water heater's tie in point to reduce the chances of something flowing back into the HVAC system if the heater ever has to dump into the drain pipe. The HVAC system is a Carrier model FV4CNF003 if that helps.

Diagram of potential solutions

So, with all of exposition out of the way my questions are:

  1. Can I tie the water heater overpressure relief line into this drain line safely?
  2. If so, would a flexible hose synched over the copper pipe and inserted into the pvc one be the best way to do it?
  3. Can I replace the existing pvc pipe layout with one of my proposed arrangements?
  4. Regardless of 1-3, is there a way to close off the floor drain in the other room?
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No it would not be safe. I do not know the settings of your valve but I expect the water would be in excess of 180F or about 82C, to over the boiling point of water,it is under pressure. That will leave a nasty burn if you come in contact with it. If you check your building code you will probably find PVC pipe is not rated for use with hot water, your proposal would unsafe. Some of the pipe materials rated for hot water are CPVC, copper, galvanized, and PEX, check your local code. This hot water will be under pressure and could blow the PVC joints apart as well as soften them and they may collapse,and then who knows. You might consider putting a drain on the side of the overflow pan, but check with your local inspector to be sure it will be approved.

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  • Fair enough, can't really argue with code. Do you think there's anything I can do with the floor grate?
    – 5E4ME
    Jul 26 at 17:07
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    From what I can see that drain is in cement. I am assuming you do not want to cut the cement or move the wall. I do not think that drain is causing your moisture problem considering it is a basement. The easiest way is to circulate the basement air through the whole house, that is what I do. My furnace blower runs 24/7 summer and winter. You could find a small plastic container that would cover the drain with a bit to spare, cut a notch and place over it. Then place some piece of furniture such as a stand over it to hide it. That way if you have problems you can get to it readly.
    – Gil
    Jul 26 at 17:22

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