Vent needed on condensate drain?

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TJanak

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Didn't get any bites in the HVAC forum and I guess this is more of a general plumbing question:

Had a new air handler put in the attic and I need to hook up the condensate drain. It is 3/4 PVC and has a P trap and tee's into the bathroom sink vent in the attic. The old PVC drain had a vent immediately behind the P trap which consisted of a T pointing up with a 6" piece of PVC glued in it. The vent was taped closed when I bought the house.

Is the vent needed? It's about an 8' run from the air handler to the sink vent with one 90* bend in the line and the P trap about 18" from the air handler. The way it was setup we never had a problem with sewer smell in the house or attic.

Thanks!
 

Shacko

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Most of the time the manufactor of the unit dictates how he wants the drain run and its configuration.

My guess is that the original line vent was taped up because sewer gas was leaking into the area; no matter how you hook it up you have to remember to keep water in that trap when the unit is not being used.
 

Cacher_Chick

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As long as the condensate drain is connected to the home's plumbing, a trap is needed to prevent the sewer gas from entering the space. The trap could be plumbed in such a way that a vent is unneeded, but depending on the layout it may be easier to connect a vent for that trap to a plumbing vent.

As shacko stated the biggest potential problem is that the liquid in the trap could evaporate if the A/C is not used regularly.
 

hj

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The vent has nothing to do with sewer gases. It is to prevent siphonage of the unit's trap, especially when the outlet drops down to connect to a sink tailpiece, which is where it should be connected. If the condensate is connected to a sink vent, (which is usually not permitted although it is often done), there is absolutely no way to prevent sewer gases from entering the building, regardless of whether you smell them or not. The air handler is creating a negative pressure in the condensate drain, and unless the trap is deep enough, AND there is condensate to keep it filled, (which does not happen if the air condition is not used such as mild weather and Winter), the sewer gases will be drawn in.
 

TJanak

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Is there some type of acceptable flexible line that can be used to run down the wall to the sink tailpiece? I saw that done in a house before.

The air handler has specs for the trap which mine meets so hopefully it will work fine. If not I'll change it. I don't think we have much in the way of problems with traps drying out here. It's pretty humid and the A/C is not off for long.
 
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