AC Drain

What are your thoughts on this set up?

Should have a trap.

I wonder is a trap required when it is open at the top of the T?

… Cookie

And the “T” should be taken out and replaced with solid closed piping. The hole in the plenum for the drain should be sealed as are the openings for the refrigerant lines just above. Both of these items are allowing conditioned air leakage to the mechanical room.

In residential duct systems, research has found that 20-30%+ of the air moving through the fan or air handling unit (AHU) does not come from or get to areas for which it was designed!! This is one reason why some rooms/areas may be hard to heat or cool. The HVAC unit may be properly sized for the building but if air isn’t moving properly…the system ain’t gonna do its job.

I have rarely (and I mean RARELY) seen sealed and insulated residential ducts in my area for air conditioning systems! If anyone has access to *HOME ENERGY *magazine, check the articles about duct leakage and sealing. Their website is: . It appears to be all subscription nowadays. A quick search showed over 40 articles with “duct leakage” mentioned.

This is the first time I have seen anything but PVC used for a condensate drain line. I wonder, since the lack of constant flow of water would cause that galvenized T fitting to rust and clog the line. Why use copper and a galvenized fitting? There is too much potential for corrosion in my opinion.

I think it is fine… It meets all the requirments that I can think of right now, but I could be wrong, I would need to check the code, and I suggest you do the same.

I have a feeling that the trap is conceiled in that box, but if not BK is absolutly correct.:smiley:

Pictures are soooo hard to analize…

I have a feeling that the trap is conceiled in that box, but if not BK is absolutly correct.:smiley:

9-12 days left.:(:D:cool::mad: I just don’t know…:frowning:

There is no cap on the T, allowing air to enter or escape unit. Without dismantling the pump, I am speculating there is no trap.

  1. Old galvanized fittings are so hard to remove without destroying the “A” coil’s drain pan.

  2. The tee is good for a clean-out but could have a plug installed. (many are left open)

  3. Copper pipe used for condensate drain lines sweat.

  4. No trap necessary and no reason for one unless it’s connected to the sanitary sewer and then it would need an air gap.

A trap is always necessary! As the air is pushed thru the A-coil it can create a vacuum on the drain at the tee or from the drain line itself. As a vacuum is created the condesate water may not run out, it may then build up & overflow in the A-coil pan down into the furnace or duct work, rusting & rotting where ever it goes. This is the same way a power washer with a soap injector works.
If draining to a sewer drain, an open drain system is required.
If draining to the outside, a closed line is OK. Installing an air vent is a good idea after the trap, but not before.
With that system you also have a galvanized to copper connection. These 2 metals corrode each other.

With all due respect;

On the thousands of systems I’ve ever seen or installed in the last 40 some years, the air pressure blowing out actually helps the condensate water drain out faster and better.

The only time a trap is needed other than what i mentioned above is **IF **the drain stub is on the negative pressure side of an evaporator coil where the blower is sucking air through and a suction is created, drawing the condensate backwards up the pipe.

Maybe this is a local thing but there are NO traps on any AH’s/furnaces around my part of the country with the exception of a few mentioned above.
Most of the condensate drains are just terminated on top of a floor drain, there are very few indirect drains with air gaps or in the case of second floor/attic units most terminate outside.

“The IPC specifies that the piping material for the condensate drainpipe should be cast iron, galvanized steel, copper, crosslinked polyethylene, polybutylene, polyethylene, ABS, PVC, or PVC pipe or tubing. All components shall be selected for the pressure and temperature rating of the installation. The UPC species that the condensate drain piping shall be constructed of material specified in Chapter 7, which deals with sanitary drainage. Therefore, all condensate drainage piping shall be the same as that for sanitary drainage. One problem with this is that the smallest drainage pipe is 1¼ inch, and many times the condensate drain pipe is ¾ inch or 1 inch. If this is the case, water tubing or pipe must be used.”

All manufacturers I’ve encountered require a trap on a condensate drain under positive pressure, if you see an untrapped discharge, check the manufacturer’s instructions; an untrapped positive pressure condensate drain is exhausting cooled air to wherever the drain is discharging. The secondary should be trapped for the same reason - some AC techs suggest using mineral oil for the trap seal on the secondary as the oil does not evaporate.

This, from is from the Trane web site, is typical:

“A properly functioning (and properly designed) condensate trap provides for discharge of water from the cooling coil drain pan, while the water seal (the water level maintained in the trap) prevents the flow of ambient air into or out of the air handler. Several problems result from improperly trapped systems, some of which can severely impact indoor air quality. Our discussion will center on negative pressure systems, since trap failure in a positive pressure environment simply results in air being exhausted through the drain line.”

That we see it done otherwise “all the time” does not make it “right”.

That is very interesting but at the same time very strange because there are at least a couple of million 3/4" un-trapped condensate drains around here.

None of the HVAC installers would ever think of putting an unnecessary trap on a condensate line.
keep in mind most all are terminating inside, close to the air handler/furnace on top of a basement floor drain.

I’ve yet to see any manufacturer’s instructions that ever suggested installing an unnecessary trap albeit I’ve not installed every brand, only a few so that leaves many I haven’t seen.

Yes, a little cold air is lost but percentage wise it’s just a tiny drop in the bucket compared to several 6/7" pipes discharging the air.
I mean, you can’t force very much air through a 3/4" pipe no matter how hard you try.


Remember that residential duct systems, in general, leak a hell of a lot of air- 20-30% by a few estimates and some research!! By contrast, well designed and installed engineered systems that undergo air leakage testing as part of the commissioning process (I used to do this) fail at 3-5% air leakage (depending on the specifier)…the contractor is then back to sealing all ducts again…a bad thing.:roll::shock::sad: In residential, any leak of 2-3+ cfm should be addressed since it’s a larger % of a smaller airflow in the 7-800 to 1500-2000 cfm residential range versus 5-15,000 cfm in commercial and similar sized buildings.

We should be setting our sights higher, maybe doing some re-training and if all else fails (I’m sure you’ve heard this before), read the instructions.

The only unit that should not have a trap is when the unit has a sign on the side of it that says it’s not required.

The loss of the little bit of air is not the MAJOR concern. Think about the big picture for a while.