Reuben's Home Inspection Blog


Trapping Your Condensate

In approximately 99.2% of the houses that I inspect, there's a 3/4" hole in the air conditioner ductwork that lets air blow out where it shouldn't.

Can you guess what it is?  Here's a clue.

Bad AC Condensate Drain

Do you see it?  It's that clear tube coming off the condensate drain pan on the air conditioner's evaporator coil.  As the air conditioner runs, warm air from the house blows over the evaporator coil, which removes heat and moisture from the air in the house.  The heat gets carried out of the house via the air conditioner's refrigerant lines, where it gets dissipated at the exterior of the home.  The moisture gets removed from the air through condensation, and that clear tube carries the condensate to an appropriate disposal location, such as a floor drain.

The problem with most condensate drains is that not only will they carry condensate away, but they'll also allow air to blow out through the drain, which is ineffecient.  When ductwork is properly installed, all of the little gaps and holes in the ductwork get sealed up, including the hole created by the condensate drain.

To fix the hole created by the condensate drain, a trap needs to be installed. This trap will work  the same way that any other plumbing trap works; the water sitting in the trap prevents sewer gas (or in this case, air) from coming through.

In my opinion, the best kind of condensate trap is a pre-manufactured condensate trap, such as the one pictured below by EZ-Trap.  These kits have a clear plastic trap, so you can see when the trap gets filled with gunk.  These traps even come with a little cleaning brush so you can easily clean out the trap when needed.

EZ Trap

The other type of trap is a field fabricated trap, which takes a little more to assemble and isn't so easy to clean, but is also far cheaper.  These can be easily assembled with a few cheap plumbing parts.  The photo at the top of this blog was the condensate drain at my own house... dontcha love how the plastic was wrapped with metal tape to keep it from melting where it touched the furnace vent?  Ha ha.  That wasn't my doing.

The photo below shows my homemade (or if you want to sound professional,  "field fabricated") trap, which took me about 15 minutes to put together with about $5 worth of CPVC fittings.  I also replaced the entire plastic condensate drain with 3/4" CPVC, which won't kink or get knocked out of place.  How easy was that?

Reuben's Condensate Trap

At the moment, everything has been dry fit together, yet it still holds water.  I suppose I should use some CPVC cement and make it permanent.  Whenever I do, I'll just have to remember to not glue the cap at the top.  I want to leave that accessible for when I need to clean the trap.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 12 commentsReuben Saltzman • June 07 2011 06:32AM


Thank you for the post. I will check my air conditioner and see if it needs to be looked at .

Posted by Gita Bantwal, REALTOR,ABR,CRS,SRES,GRI - Bucks County & Philadel (RE/MAX Centre Realtors) over 7 years ago

Hi Reuben, and welcome back. I run into the same problem. Most home just have the condensate line running into the pan, then outside. No trap. I talked to a very experienced A/C guy and he laughed at me.

They need to be educated "WHY" this trap is needed.

What reporting software do you use?

Thanks for the post.

Clint McKie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) over 7 years ago

HI Reuben - Very informative post! I hit Suggest.

Posted by Judy Klem, Home Staging, Senior Move Management, Fairfield/New Haven counties (Transition Stage LLC) over 7 years ago

Gita - let me know if you have a trap :)

Clint - what, you mean the AC guy didn't know what the purpose of the trap was?  I don't make any big deal about this during my home inspections... in fact, I usually don't even mention it, but now that I have a blog post to include a link to in my inspection reports, I'll probably start mentioning it on a regular basis.

I use Porter Valley's "InspectVue" software...  and I don't recommend it.  I just use it because I have it, and switching software would be way too difficult right now.


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Judy - thanks!  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Like the EZ-Trap kits that have a clear plastic trap, so you can see when the trap gets filled with gunk and brush it out.

Posted by Daniel H. Fisher, MCRP - Charlotte Real Estate, NC or SC ( (704) 617-3544) over 7 years ago

Most of the time I see the loop just made from the clear plastic line being tied in a loop over itself. This way you can see the trapped gunk in it but yoy have no access to clean it. 

I recommend getting rid of them. Its just a place for mold to grow in. The volume of air that would exit this way is not significant. Any situation where it is significant then also has enough pressure to blow the trap clear, rendering it ineffective (as a trap).

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 7 years ago


Correct me if I wrong but the Condensate trap is only used if there is not an internal trap and that it AC coil is on the positive side of the unit.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 7 years ago

Daniel - I like those too.  I had one at my last house, and it actually stayed surprisingly clean.

Robert - funny, I see the loop on HRVs all the time, but never on AC condensate drains. 

As for the mold thing... I had one of those EZ-Traps at my last house for about seven years, never had any trouble with mold.

Donald - condensate traps should be used whether it's positive or negative pressure.  If there's a system that exists with an internal AC condensate trap, I'm not aware of it.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

I just did a turnover inspection on a new home yesterday. The HRV drain had no trap and neither did the AC condensate drain. The AC unit was built into the furnace stack (gas fired) and that had another drain under everything. This had an open cup trap on the side. The cup has a lip which pours into a 3/4" pipe running to the floor drain.

I discussed this with the supervisor and their contractors started not doing these closed traps over 5 years ago.  They experience no air bypass in these lines. The traps are considered an unnecessary maintenance problem. Some have concerns for health issues.

Most condensare drains run for 4 to 6 feet down from equipment, around room corners, etc, to the floor drains. They discharge high enough so they are not cross-linked and the floor drains have their own water traps. The length of piping and number of turns is considered a sufficient nullification of any potential blow-by air pressure in the lines.

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 7 years ago

Actually I see your field fabricated trap all the time!  Yours is really cute though.  I hope it catches on!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 7 years ago

I see this on the home inspections reports constantly -- you are absolutely right about that.  Now I have a much better idea, why!

Posted by Eric Crane -- Your Full Service, Discount Fee Realtor®, Greater Metro Phoenix Arizona (DPR Realty LLC) over 7 years ago