Condensate drain blowing cold air

Looked at a home built in 2006 with a Goodman Mfg. split system, gas furnace in attic, condenser outside.

The condensate drain line first had an upright piece of PVC, open on top & blowing cold air, then a P-trap. It ended into drain piping under a vanity sink.

Should the upright PVC be capped, or should the P-trap be before the upright PVC?


The P- trap was installed to prevent odors from the vanity drain line, being open will defeat the P-traps intended use, in the winter, the water in the p-trap will evaporate. It never should have been connected to the drain line, it should exit outside.

Actually I was told the p trap is there because the drain is hooked up to a pressurized system. The lack of a cap defeats the design. Cap it.


Actually you both are right


I’m not an expert by any stretch of the imagination, but I’ve seen the primary drain line’s P-trap with and without the cap in place. Obviously if the cap is not there, cold air will blow out of the top (just as it would through any hole in the casing). Generally though, I’ve seen has the cap in place, not glued.

Concerning the quote above (and again I’m not a pro), but the primary drain is supposed to drain into the home’s drainage system and not into a vent pipe (though I see this often enough). It is not supposed to drain outside. The secondary line may drain outside though.

I’ve not taken the time to look this up, so I’m flying solo with my memory. :smiley:

My .02 cents,

The vent configuration described is normal. The vent is just that, a vent. The drain termination at the interior bathroom sink drain plumbing is normal as well. If the condensate vent is capped, you’ll begin to hear a popping suction sound at the sink drain termination. A certain amount of air loss at that vent is also acceptable.

Ken, I think you may be thinking of the over flow catch pan drain line which indeed should terminate to the exterior over a window. This would provide notification of an issue at the attic mounted unit. The primary condensation drain lines can terminate at the interior waste line plumbing and or exterior of the structure. I witness both here in California on a daily basis…

Where’s David Anderson when we need him. He seems to be a wiz at HVAC. I’m sure he’ll have all the technical speak on this scenario…

That condensate drain line looks good to me, but why would it be insulated?

The water from the evaporator coil is quite cool to cold therefore cooling the drain line to cause exterior condensation and dripping. The insulation with joints sealed prevents the interior house air from contacting cold pipes; its surface is at or near room temperature …no condensation.

Not exceptable

Not exceptable either

My name is not David but here is my take on this.

Condensate drain lines should not be connected to the sewage drainage system under any circumstances unless the Furnace is a high efficiency furnace which is exceptable because it is a continious flow trap and does not go dry in the heat season.

We basically have two types of A-coil designs postive pressure and negative pressure. Lets look at both types and discuss when and where cross connection between air stream of the furnace A-coil and the drainage system can occure.
Postive pressure coils will have a cross connection in the heating season during the times when the blower is not operating and the P-trap is dry.

Negative pressure coils will have a cross connection during the heat season when the P-trap is dry and when ever the blower is in operation and when it is not in operation.
So what I am basically stating the primary drain should never be connected to the sewage drainage system on a 80% furnace with a direct drain line. The drain has to be an indirect drain (air gap) required

To David Valley in the Pic the condensate drain line was insulated because it was in the attic and will sweat see them both ways is not required one way or the other.

It is prefectly legal to discharge the condensate exterior to the home as long as it does not create a problem to someone else.

I Believe the vents are connected to the sanitary drains???

Perfectly legal to discharge exterior to the home unless it creates a problem to the general public.

The secondary drain should discharge to a visible area to the homeowner.

I believe the opening is often included in the primary drain for the purpose of adding bleach annually in order to keep the drain free of algae. I’ve heard its purpose described that way. I see nothing wrong with it uncapped–if I wrote that up, I’d be writting up 80% of the condensate drains I see.

I don’t write up missing caps either but sure do if the drain is connected to the sewer through a direct drain must be indirect or to the exterior. Yes the vent is a good way to add bleach unless the vent was placed on the outlet side of the trap. Traps is where most cold water slime forms to begin with.

Vent should be installed down stream from the condensate p-trap.

In hot-humid attics it is also advisable to insulate the condensate drain lines to avoid condensate forming on the pipe exterior and dripping onto attic surfaces, insulation, wood, drywall…

Advisable to install overflow switch on the drain pans when located on second floor or in attic

Secondary drain should not be plugged or capped

Barry, it is installed as your clip on the left - except placement of the upright open vent.

  1. furnace 2) piping with upright open vent 3) p-trap 4) drain line to lavatory tailpiece

Also, cold air can be felt coming from corner of furnace cabinet where the flue vent pipe connects, as well as the upright un-capped vent pipe.

I am going to call for service. House is one year old, unit runs continuously through the day. 1,774 sq/ft, 3 ton unit. Thermostat was set at 77 degrees, showed 80 degrees in room. Didn’t shut off while we were there. Outside temp a balmy 88.

100_8235 (Small).jpg

My air handler unit is in my attic and never sweats. I’ve just never seen insulation on a condensate line. Oh well.

That makes perfect sense. I didn’t catch the location of it prior to the trap.

From a typical Lennox manual. Trap both the primary and secondary (if connected to a drain), cleanout(s) go after the trap:

Cond - Trap Lennox Diagram B.gif

Ah! Finally a good diagram of what should be done. Thank-you.

Barry’s diagram is better. :smiley:

Nice digrams Barry.