Which condensate drain is better?

[Layne]

This will not be inspected, I just prefer to do things as correctly as possible.

So I have a loft above a laundry room that contains an air conditioner and a water heater. I need a place to drain the a/c's condensate and also to connect the drain pan for the water heater. Initially I planned to install the green trap shown creating a wet vent for the washer, but it seems this is not recommended since the trap may evaporate dry in the winter. This is not a residence, but a residence-like area in a shop/warehouse, so it's almost as likely that the washer could go months without use too. The alternative is the red pipe, teeing into the washer's standpipe. This avoids the dedicated trap drying out in winter, but I'm not sure if teeing into the standpipe is an acceptable practice. The blue pipe is an optional vent for the green trap. I know "every trap must have a vent" but logic tells me that a mere trickle of water going through a 1.5" trap could not possibly need it. But it's easily doable.

Bonus question: May the water heaters T&P drain pipe end just above the drain pan? I understand the T&P may not go directly to a drain pipe and must have a visible air gap (the loft is debatably "visible"), but can that air gap be over the drain pan? Obviously if the valve failed there will be much splashing and steaming, but the pan could catch most of it. The alternative to that is to drill through a nearby concrete wall and put it outside, but only if absolutely necessary. I see T&Ps connected to nothing more often that not and probably wouldn't think much about it if I hadn't experienced one failing before.

 

[Terry]

The condensate can go into the washer standpipe. They recommend that tankless water heaters run theirs to a washer drain too. The acidic condensate gets neutralized by the soap from the washer.

The T&P is normally daylighted six inches above. They prefer it outside, but sometimes that can't be done. A roto hammer does a nice job on concrete.

 

[Sponsor]

 

[hj]

IF the T&P valve discharges, the pan will "catch most of it" for about 10 seconds and then it will overflow onto the floor. The condensate drain SHOULD go to the washer standpipe, and the T&P valve to the outside of the building.

 

[Jadnashua]

Depending on where you live, running the T&P outside may not be a great idea. Works fine in areas that don't get really cold, though. It's not unusual for a T&P to drip or dribble a little, and if it drains to the outside and it's much below freezing there, it could eventually block the pipe. Then, if the T&P needed to open because of a WH fault on a bigger scale (a slow dribble may be from something like a closed system and a failed or non-existent expansion tank, or someone tested the thing, there was some mineral deposits, and the thing never sealed again), the pipe would be blocked and that could defeat the safety of the valve itself.

If the T&P opens fully, the flow could easily overwhelm a drain, and would fill the drain pan quickly. There are devices that can detect that leak and shut the water (and the WH) off. I'm not a fan of putting the WH in finished living space or areas that would see a lot of damage if they got soaked unless it is engineered well to offer some protection. All WH leak eventually. It's when you catch it that determines if there will be an issue or not.

 

[Bluebinky]

Yes, the trap in the attic would need to be kept full somehow.

 

[hj]

quote; It's not unusual for a T&P to drip or dribble a little,

IT is not only 'unusual' but a sign that the valve has failed and needs to be replaced.