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Condensate drain trap?

jay kline

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From our folks over at ITA.

Dear Inspector,

This month I would like to discuss air conditioner condensate drains. I seem to see much confusion regarding drain configuration and termination.

First, a condensate drain is not required to be trapped by any of the Codes. Most manufacturers of air conditioning components require a trap on the primary condensate line to keep conditioned air in the air handler and to prevent insects from entering the air handler through the condensate line. A vent (some manufacturers call it a clean out) is usually required on the outlet side of the trap (install on the air handler side would negate the purpose of the trap) by the manufacturer. Most new models have a sticker on the air handler at the drain tapping showing proper drain configuration.

Most of the time condensate is gravity drained (meaning sloped to drain its entire length) to the exterior grade by a PVC or other pipe. The termination is usually visible, but not required to be visible. The secondary, or emergency drain, should be visible to alert the occupants of a problem. Since most layperson occupants have no idea water flowing from this secondary drain indicates a problem, many technicians are now installing a float switch in the drain pan and/or secondary line to shut down the system in the event of a primary condensate drain malfunction. A non-working system usually promotes a phone call to the service company instead of the usual ignoring the water flowing from the secondary.

Many jurisdictions have provisions for alternate methods of condensate disposal besides just draining to exterior grade or a floor drain. Any connection to the sanitary sewer system will require a trap. This is called an indirect waste by the Codes. Many times I see condensate drains terminating at trapped receptors (a standpipe, like used for the clothes washer) connected to the sanitary sewer system. Traps installed only for the condensate drain will require trap primers to keep them wet. Because of this problem the most common termination locations are routinely wetted traps such as lavatory sinks and bathtubs. The fixture keeps the trap wet to prevent sewer gas flow back into the air handler. The condensate is connected with a branch tailpiece on the fixture side of the trap, such as to the outlet of the lavatory sink or the overflow of the bathtub. Connection to the sewer side of the trap is improper and will result in sewer gas flow to the air handler since the condensate line trap (if installed) will dry out in winter. Another common location for condensate disposal is the clothes washer standpipe.

Condensate pumps are commonly used where gravity drain is not possible. These pumps accept the condensate and pump the liquid to an approved location once the tank is filled to a predetermined level. The outlet pipe from the pump is not required to be trapped. The inlet from the air handler should be installed per the manufacturer recommendations, which could be trapped or not.

Hope this clears up some questions about condensate.

Mike Casey

Inspection Training Associates

Now You're Ready For Business!â„¢

On commercial rooftop equipment you need a trap on a evap coil that is on the negative side of the fan. Without the trap the fan would keep pulling air in through the condensate line and the water would never flow out. This can cause carry over of condensate through the fan and into the duct work. When the fan shut down you then get a big rush of water out of the condensate line. When the evap is on the discharge side of the fan the condensate flow freely.

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Jim - sorry. I should have been more to the point with my question. Maybe a better way to phrase it would be: Since the condensate drain line is not supposed to be connected on the waste side of a plumbing trap, what is the point of installing a trap in the condensate line?

Terence's response answered my ill-asked question very well. I have been writing it up when I cannot locate a trap on the primary condensate drain line, but until I read Terence's reply - I didn't know why one should be installed on a drain line that is properly terminated on the fixture side of a plumbing trap. I was thinking only of the need to prevent sewer gas from entering the system - I had not thought about the need to keep conditioned air inside the air handler or to keep insects out. Thanks Terence.

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Thanks for the link. Perfect timing too. I had a secondary unit in an attic space today with a trap that was at least 2 feet long. The drop from the A/C was pretty good but the furnace drip was only about 6 inches With the 3 inch rise and 2 feet of run. I had to laugh, Thanks![:-snorkel

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