HVAC P-trap plumbing question

[green.bubbly]

Inspector came today for roughin inspection. He cautioned that my my HVAC p-trap could dry out in the winter time and **** in sewer gas from the vent pipe that I attached the condensate drain to. The vent where I attached the line runs horizontal across the ceiling and then outside.

He suggested that instad of connecting it to a horizontal vent line, that I connect it to a vertical vent line and he pointed to a spot on on of my vents about 6 feet above the ground. As he pointed, he said something about putting a p-trap here and attach my condensate line there.

I was a little confused but I damn sure was not going to keep him there any longer than I needed since he had already passed my inspection.

I understand that during the winter, there would be no condensate entering the p-trap and it could dry out. Where I am confused is that even if I put it where he suggested, there would still be no water source to keep it filled.

I found a picture online which kind of describes what he suggested but the article with the picture said that this was not acceptable. If you look at the pic below, it looks like the hvac drain line enters at the top of the picture and drains intp the large p-trap on the vertical vent. Again, there is still no continous source of water.

The only thing I can think of is that because that trap is larger, water will not fully evaporate during winter.

 

[Falcon67]

I personally would not run a condensate drain into a vent stack. It should be run outside on it's own. Yes, water in the p-trap will evaporate. It does shortly out of 4" drains, so it'll go quick out of a small trap. The only place I've seen a p-trap on a condensate drain and one that ties into a vent stack is the 4 ton AC unit in my work's basement data center. It's a **** place for a data center, but the AC runs 24-7 so there is always condensate in the little 1/2" trap.

 

[green.bubbly]

I would run it outside but here in hot and humid Louisiana, my yard would turn into a swamp. I have seen people run it to a sink drain like a dishwasher setup.

 

[Grumpy365]

I personally would not run a condensate drain into a vent stack. It should be run outside on it's own. Yes, water in the p-trap will evaporate. It does shortly out of 4" drains, so it'll go quick out of a small trap. The only place I've seen a p-trap on a condensate drain and one that ties into a vent stack is the 4 ton AC unit in my work's basement data center. It's a **** place for a data center, but the AC runs 24-7 so there is always condensate in the little 1/2" trap.

Pretty sure that is against code in most places.

I THINK code says you have to have the primary drain tied into a facility or building drain (not vent, but stand pipe) and the secondary drain to the outside.

My house has the secondary drains come out over a window so you can see if there is a problem / clog in the primary drain from inside. I don't know if the window part is code, but I think the other parts are.

EDIT: no national code says you can't run primary drain outside. Local codes vary.. It just says you can't "discharge into a street, alley or other areas where it would cause a nuisance"

And the secondary needs to terminate in a " conspicuous location" hence why my secondary drains are over windows.

Sorry for the misinformation.

 

[Jackfre]

Personally, I like to see them go into what is called an indirect drain. What this means is there is an air gap between the drain line and the trap assembly. The condensate drips into the standpipe which leads into the trap. The best place to terminate a condensate line is outside on its own if that is climatically possible. Otherwise try to run it to the washing machine indiect drain. That trap will not run dry...generally

 

[green.bubbly]

Personally, I like to see them go into what is called an indirect drain. What this means is there is an air gap between the drain line and the trap assembly. The condensate drips into the standpipe which leads into the trap. The best place to terminate a condensate line is outside on its own if that is climatically possible. Otherwise try to run it to the washing machine indiect drain. That trap will not run dry...generally

So basically try and run it to a drain before the p-trap similar to how a dishwasher would be plumbed to the sink drain???

 

[green.bubbly]

Pretty sure that is against code in most places.

I THINK code says you have to have the primary drain tied into a facility or building drain (not vent, but stand pipe) and the secondary drain to the outside.

My house has the secondary drains come out over a window so you can see if there is a problem / clog in the primary drain from inside. I don't know if the window part is code, but I think the other parts are.

EDIT: no national code says you can't run primary drain outside. Local codes vary.. It just says you can't "discharge into a street, alley or other areas where it would cause a nuisance"

And the secondary needs to terminate in a " conspicuous location" hence why my secondary drains are over windows.

Sorry for the misinformation.

I have my secondary drain exiting over a bedroom window. It will drip on the concrete if it ever overflows. Hopefully we would see it through the window or at least when cutting the grass.

Plus I have an over an overflow switch.

 

[Orangestang]

Could you install a horizontal check valve to keep it from drying out and sucking fumes... To install a condensate drain in a vent stack is a no no around Chitown.

 

[Falcon67]

An option might be what they used in the house around the corner. The AC unit is a vertical and sits in the middle of the house. They used a small sump pump and ran a line up and over to the outside. Water collects in the sump and eventually triggers the pump. You could run that to a sink drain somewhere. I get your Louisiana humidity issue, having lived in Houston.

I have my secondary drain exiting over a bedroom window. It will drip on the concrete if it ever overflows. Hopefully we would see it through the window or at least when cutting the grass.

LOL - the two story we had in Houston ran the secondary to the eve over the patio. If the main was plugged, when you went out the back door you got rained on. Hard to miss that one.

 

[Jackfre]

Yes, kind of! You want an "air-gap" between the drain pipe and the condensate pipe. The drain line just drips, by gravity hopefully, to that standpoint, and it being a washing machine will not have such long periods of non-use that the trap will not dry out.

Falcon's suggestion of a condensate pump is common but I try to avoid them like the plaque. Just one more thing to screw up on the hottest day of the year with a house full of people. Also, the pump should be wired to the ac unit so that when it stops working the ac does too. You do want it that way. Also, be aware that condensate lines, because they are chilled will condense on the outside to the drain line. Insulate them to eliminate any sneaky future mold issues.

 

[green.bubbly]

Why the air gap? I was thinking of putting one of these on the spare bathroom sink and connecting my condensate line to it.

 

[JakeKohl]

Why the air gap? I was thinking of putting one of these on the spare bathroom sink and connecting my condensate line to it.

I have two mini-split systems in a garage with a full second story on top of it. They drain into plumbing in the wall and terminate exactly that way into a downstairs sink drain before the P-trap to avoid making mushy ground outside.

 

[maxspeed96ct]

Your inspector had a good point. But the location he told you tie into wasnt 100% right either. I think what he ment to say was to tie it into another trap that is often used and normaly has water in it.


Air gap wouldnt realy solve your problem. You would still need to change your tie in location . Sewer gases would just come right out in the air gap.

Also if you have a house trap on your main line going out like some older homes do you wont have to worry about the smell either way.

As far as I know its not illigal to run it outside but that might depend on your local codes.

 

[green.bubbly]

Your inspector had a good point. But the location he told you tie into wasnt 100% right either. I think what he ment to say was to tie it into another trap that is often used and normaly has water in it.


Air gap wouldnt realy solve your problem. You would still need to change your tie in location . Sewer gases would just come right out in the air gap.

Also if you have a house trap on your main line going out like some older homes do you wont have to worry about the smell either way.

As far as I know its not illigal to run it outside but that might depend on your local codes.

I think you may be right. I think he just put his hand on the vent stack of my spare bathroom sink drain suggesting that tying into the ptrap of this branch.

 

[2Big2Ride]

So basically try and run it to a drain before the p-trap similar to how a dishwasher would be plumbed to the sink drain???

You got it. That is how the primary drain is done here.

 

[curiousB]

I think the dishwasher feed before the trap of an existing sink is the best bet.

This is a similar problem to floor drains in laundry rooms. They exist to catch water in a crisis overflow so typically the trap never sees water. They make trap primers for such situations to give a little spritz of water to the drain. Seems like a too much trouble for your application though.

http://en.wikipedia.org/wiki/Trap_primer

Water softener discharge is also a challenge. But they run year round so less chance of trap drying out.