You young guys getting into the trade are very lucky to have access to this guys videos. I wish I had them 20 years ago.

The amount of things that I can learn from Craig in a day is ridiculous 👍🏿 thank you for all of this information and helping people become better techs

Make sure to always add a tee on p trap. Clean out is needed especially in a attic

Wanted to comment on your latest vid in the hopes you see it. I spent hours watching your videos in order to fix my HVAC system. I know you teach to help the pros but I hope you dont mind that you help a lot of DIYers like myself. I took the time to watch many videos on your highly accurate and detailed inspections and repairs of HVAC systems and in the end I was able to fix it myself. Thank you so much for all of the videos and just know youre helping so many. Cheers!

Here in Florida the majority of houses are built on slab foundations with the line set and condensate line running under the slab in 3 or 4 inch pvc. The exit point for the condensate line is outside the house and rises up 8 to 10 inches above ground level. This creates a natural "P" trap as the under slab vs the exit point in total is about 15 inches, trapping the water in the line. Therefore no "P" trap is necessary. Depending on your construction it may or may not be necessary to add a "P" trap.

For 13 years my Nordyne 4 ton unit drained out what I thought was a pretty good condensate "drip". It had NO p-trap. After watching a previous video you did, I installed the Rectoseal trap and turned the condensate drain into a small garden hose. Everything equal, I dropped the RH by 5%. To test how well this works I opened up the cap between the trap and air handler and added food coloring and let the unit run. The food coloring just sits there. Closed the cap and off she goes.

Wow 😮 Now I’m even more freaked out. I’m a first time homeowner. I watch these videos all the time trying to learn what I should be doing. My AC is on the second floor in a closet. It ducts out from there. Another video told me I should flush the pvc drain pipe with vinegar. But my drain pipe had no cap to open to pour in vinegar. Apparently that’s not unusual because there was a video for how to cut a T valve in. But now you added a p-pipe. I don’t have that either. Where does that go? Before or after the T-valve? The prior videos just warned that the drain pipe had to slope down from the AC. 😱

Thanks so much! I moved into a house with a furnace/ac combo and it over flowed. I had to figure it out at 1:30 am! I had to cut the pvc pipe- I was going to put another trap- but now know I don’t need one. I can just use the pump. So grateful!!! ❤

Just found your channel. I have been having HVAC/Furnace issues with my drain line so have been looking at KZfaq to better understand what I don’t know. I have seen a lot of videos on drain lines, p-traps, air exchangers and exchange coils and this is THE BEST of all that I have seen. Your explain the different requirements for air handlers HVAC), exchange coils (Furnace) , and mini split systems. FANTASTIC. Thank you!

Those visuals, as simple as they seems, are priceless to adress the mindset toolbox of any tech. Thanks forever Craig!

Best video ever 10 stars and 10 thumbs up. Specially now that I am about to install a heat pump and I had been searching for this answer since I didn't know the requirements for it and also because I new ducted and ductless work differently and also because I was debating whether to drain it outside or inside into a drain or even a pipe that drains my kitchen sink but was concerned about sewer gases backing into the drain pipe.

Great Video. In some positive pressure situations, a trap may still be needed. There's a youtube video out there where they use a clear evaporator chamber where the positive pressure is high enough to cause the air flow escaping from the drain to actually push the water away from the drain hole preventing it from draining until the system shuts off. It's similar to what happens with negative pressure but there's positive air flow pushing through the drainpipe. A trap in that case will prevent that. It will also prevent the loss of conditioned air escaping. However, in the case of the overflow, when it is drained outside the house, air will always be able to escape the system. A trap on that line won't help because it won't fill with water until the main drain clogs. Not a problem if you use an overflow switch. Forum threads on these p-trap topics go on and on and never seem to resolve to a solution for all cases.

This man, legend

Thank you for this excellent explanation. I was confused when my horizontal high efficiency furnace had a trap on the furnace condensate drain, but not on the AC coils condensate drain.

Just what I was looking for, I was having issues with negative pressure. Great video!

You are a wealth of knowledge. The best hvac videos out there.

Great info. Helps to understand why we use the traps. Thanks Craig.

Best video on traps i have seen. Thanks

I think we should be calling the system either ‘Positive pressure’ or ‘Negative pressure’ system to avoid confusion. A good topic of discussion would be what to do with that secondary drain port for each style system.

The air escaping in your math scenario is 15.8 cfm, not 4 cfm. You forgot radius squared. Not sure why it’s acceptable to allow a loss of 15 cfm from any positive system. This would be the same as having a one inch hole in your ductwork. This makes a compelling reason to have a trap on a positive pressure system, to prevent air escaping. Nice job demonstrating the physics.

Awesome explanation of traps. Great job Craig

The first 95% furnace that I installed constantly quick cycled and I found out the the condensate plug had to be opened so the water could drain off (Yeah I finally read the manufactures instructions) I added a p-trap with a clean-out tee and it worked fine at after that.

The CFM result should be double. You forgot to multiply by 2 when calculating Area. Also considering ~8CFM coming out of the PVC pipe i would recommend adding a trap even on positive pressure system. The air will cause restriction for condensate... Thank you for the video. Great info as always.

Great job, thank you brother. You are so talented

How much of a difference would it be with air filter at the return grill? Also a slightly restrcited air filter? You the man Craig

Great and positive training, very informative, thank you so much

Great video as always. For any newbies, don’t put trap there air you won’t get your filter out 😉

Jesus I love this Channel. I just bought his mini split book. Very excited to read it!

I put a trap on my gas hvac with an ac onto. I clean it when I check the water softener salt level.

Any issues placing the trap outside if the drain line is properly pitched ?

Great video. I'd love to see how a clogged/dirty filter can affect air ingress pressure on the drain line, too. My guess is more air clog = more water column. Can a clogged filter cause enough vacuum to suck a trap dry?

As Always thanks for your great expertise !

I just had a new Goodman installed and when I asked them why they didn't use a P-trap they said it didn't need it because the condensate line comes out of the bottom. I knew that wasn't right but I did read in the manual that if you have a shut off installed then you don't need a P-trap necessarily but I'm not sure if that's a good idea. Meanwhile these guys who installed it seem like they don't know what they're doing because they didn't mention that all they said is because the PVC pipe comes off the bottom of the air handler you don't need a P-trap meanwhile even though the pan is draining there is a small leak where are the threads attached to the pan. To show you what kind of workers they are in order to try and fix the leak they hit the PVC pipe with a hammer to break it off then they replaced it but didn't use any plumbers tape so it's still leaking a tiny bit. Maybe it wouldn't be leaking if they had a P-trap even though it's not really backing up in the pan much at all. I can't trust these guys that's for sure. I also have a little bit of water dripping off the coil and not going into the pan. I mentioned that and of course they're playing dumb. Not sure what I'm going to do about that

I was so confused, not anymore! Gracias!

Good video. At 6:03, what is that small white colour tin with red colour cap? Thanks.

Great video, should I add bleach water every so often to p-trap to help stop blockage issues. Thanks in advance

Any videos on where to take line temperature readings for superheat and subcooling on packaged rooftop units??

Thanks guy. I really appreciate this.

Good job ❤️🙏🙏🙏

Does the condensation still drains while using a dry trap ? Also, should a overflow shutoff switch be installed as well ?

Excellent video. Thank you!

My Furnace & A coil didn't have a trap on it for 10 years when I moved in this old house. I seen a video online and it showed the water trapped in the pan because of no trap. I looked at my unit. It had no trap. I looked while the unit was running and the condensate was pooled because of negative air flow. It looked just like this video at 3:08 min. I put a U-trap on it a few yeas ago. The u stays full of water now. When I pull the cap, I noticed positive air flow. Why would it have negative one time and positive later on? I went to HVAC school, but I don't use that knowledge except for my personal house.

great video learning more about how ac works. ✌

So for a furnace / AC unit with a frame coil, you do not need a p-trap or even a vent to safely drain water for the condensation drain?

Ok my son purchased his first home and now is working out of town. So I have trying to help out at his house so his wife does not have to do everything. Noticed the other day water coming out a pipe in the eve of the house. So I knew it was the emergency over flow for the HVAC. When I get in the attic I notice that the water seems to be coming out I guess the emergency on the HVAC and air flow. On the main drain line that goes to the house plumbing seems the be clear flowing. Almost seems like the safety switch on the main line slows the flow or change air pressure to make it some out the emergency hole. Do know they had some warranty work done on the a/c and am wondering if they left out the drain. Will try to attach a picture so you can see what I’m talking about. Any ideas would be great!

If a condensate safety shut off switch is added to the evaporator coils overflow port, will the negative pressure not allow the condensation to enter said shut off switch?

Exlent explanation thanks for your kind information

So let me know if I have this right... The reason the unit on the left (Furnace/AC) has positive pressure at the A-Coil, and the unit on the right (AC) has negative pressure at the A-Coil, is because in the Furnace/AC (left unit), the blower is below/before the A-Coil (often between the A-Coil and the filter/return duct) blowing toward the C-Coil, and on the AC (right unit), the blower is after/above the A-Coil, blowing AWAY from the A-Coil.

Can you please clarify when to use a P trap vs. when to use a U trap on a residential air handler. Thank you.

I looked this up because I’ve been working in my attic, and since it’s transitioning into winter, it dawned on me that the water in my condensate P-trap will more than likely dry up since the AC is not being run. So I take it I should keep an eye on that in the winter and add water to it if I need to?

Is it required for both upflow downflow and fan coil? Post and prefan

I was taught to put a tee with a riser to break the vacuum is that not needed either?

Best channel on youtube

Getting ready to install new Trane 4-5 ton coil. In the installation instructions, it states: "The condensate trap is not mandatory but is recommended for efficiency". But after watching this video it would seem that a trap would be mandatory because otherwise the condensate water would not drain until the unit shut off. Any further explanation?

The condensate drain on my 90%+ furnace is completely dry. I was going to pour bleach in there as instructed by my installer to clean it. I saw it was dry, which I had never seen before. Is it normal for this to become dry during the months that the furnace isn't being used to heat the house, only the A/C is being used. Also, did you say that if my drains are not going outside but just draining into a floor drain that I didn't need a trap? The furnace (heating) condensation drain has a sort of trap but not a conventional P trap. Two tubes come out the side of the furnace into the very bottom of a retention reservoir. The reservoir will fill up then overflow into a drain connected to the PVC drain that goes to my floor drain. That reservoir is what is dry right now. My A/C condensation drain comes comes out of the top part of the furnace/AC where that A coil is. The drain then makes a couple 90% turns and is connected to the same PVC that the heating condensation drain is connected to and drains into the floor drain. The A/C doesn't appear to have any sort of P trap. Is that okay or should there be a P trap. If pictures would help, I have some I could send you.

Great video

At 3:49 there is a device... Couldnt quite make out what you called it.. my condensate line has no p trap. Its a verrical force air system. Its. A system installed in 2009. There really is no clearance to have a p trap.hvac Housing cover blocks the depth needed for a standard p trap.

Adding a trap to a positive system can cause drainage issues if you cap it.

I have a commercial AHU drain question. The drain pan inside the motor housing, when the unit is cooling, is constantly full/overflowing and water is not draining through the trap, but when you open the door to the motor housing water begins draining out of the trap. There’s clearly a vacuum effect happening because the door is hard to open. What could be done to fix this issue? The condensate overflows the pan inside and the water level is about as high as the bottom of the door and leaks out of the unit wherever it can, just not through the condensate trap like it should. Any help would be greatly appreciated

This explains my wife referring to watter weight.

I’m having a problem with air handling systems that are inside the ceiling at a gym, I’m getting water leaking from the bottom of the units, could this be due to the drain traps being full of air and not not trapped with water?

This was very informative.

Good video, thank you fro posting this.

I moved from Florida to Oregon. Combo unit furnace central A/C. Notice no water coming out the condensate line outside the house. Air is quite dry though. Notice that on my unit the pipe just above the U trap has a plug (between the coil and the U trap) that is not covered - so open to air. Is that wrong and should that cap not just be a open pipe but closed top?

What does it mean if you pull the cap on the inlet side of trap and water starts flowing into trap then put cover back on and water flow stops .

Craig, or anyone else, any word on long term usage of the DRY TRAPS? I'm searching all over the damn internet and I can't find much of anything anywhere... I can only picture algea easily building up or similar but I can't be certain. I'm just a know nothing DIY homeowner.

Great video. Thanks for sharing.

Great demos. Thanks

Nice knowledge I’m having problem with apartment the water just sit in the drain pipe but want drain . But the drain lines running in from the same drain pipe ???? Help please

What would be the effect of using a larger value capacitor on the air-handler blower? The value should be 5.0 uF (original capacitor, but someone replaced it with a 7.5 uF capacitor (both 370 VAC).

A lot of great information

Awesome video!

If the trap was empty and the unit was not draining while running, would it then fill up the trap when it shuts off? Assuming that it was not on long enough to overflow the pan.

I have a whole house dehumidifier and I piped the drain to a condensate pump; pipe just off the bottom. My hvac buddy added a trap when we were troubleshooting an unrelated problem. From your video, it sounds like I should remove the trap. Yes/no? Thanks

Thank you for this video

If you have an auto shut valve installed (like your system has) and your U-Trap clogs then the shut off valve will shut the system down before water overflows. You said it would overflow which sounds incorrect.

I dont know anything about this stuff. Should the u shaped tube have water in it always?

Thank you! Great video again. Question, if I have a horizontal air handler draining into a pump, do I need a p-trap?

With a positive pressure system many homes have line going into drain -vent stack so you need trap to keep out sewer gas right?

U trap is awesome

I have a machine similar to,the second one you show……it leaks condensate water under the two exit ports….they don’t have a crack, what is going on?

How do you configure the trap to allow access to/replacement of the air airhandler filter?

My drain line was plugged up and overflowed into the secondary pan, but I don't understand why the float switch which is attached next to coil drain didn't tell the system to stop? I pulled the float switch out and verified it does shut off the outside unit when moved, but don't know why it wouldn't shut off the unit before it started overflowing into the secondary pan. I have no P trap.

Does not having a trap cause water to drip off of the a coil?

What about a positive air flow drain without a vent? They seem to cavitate and splash the water from the pan, inside the blower..

Any help is appreciated. Air blows out from my condensate line. It doesn't have a trap right now, do I need to install one to make it more efficient?

Great Video !!!

Great information, thanks.

Craig, Thank you. Also please make a video about piston sizes. Can the piston used for r22 be used for r410a? I always install the TXV when I do only condenser change out. But I always wondering what is gonna happening if I will leave the piston without touching anything on the air handler side.

Thanks for the video =)

It is okay to have a upflow furnace with the coil on bottom, or a downflow furnace with a coil on top?

are supposed to pipe it that way on a handler ? feel like they wouldn’t be able to change the filter themselves ?

Huh I also always thought you were supposed to leave the condensate PVC just at the very top of the pump. Maybe. This is just from a furnace drain ??? And not AC ??

I have a lennox cba-024 230-01. I'm going to be leaving for vacation and have not cleaned my condensate line for the 2 years since I had it. Should I wait until I get back before I attempt to clean it. I don't want to mess it up and cause a clog.....

We just had furnace/air handler/AC units /Evaporator Coil (A coil) and outside unit replaced... as well as a new condensate pump. I went downstairs and noticed that the pvc that comes out of the furnace and drains to the condensate pump has a piece of open pvc on the top of it, and AIR IS BLOWING OUT OF IT. IS THIS NORMAL? Does this decrease the air flow coming out of the furnace and/or AC unit into the ducts?? SHOULD it be open? Shouldn't the pipe to the condensate pump be closed?

So should the U trap always have some water in it?...

Costgard condensate drain seal

Thanks!

With the second example shown (positive pressure system) I noticed the shut off valve is slightly higher than the drain vent. From the little bit of research I've done people stated that it's faulty and did not work as it should. That in order for the valve to be triggered it needs to sit slightly below the drain vent. Is this true?

Thanks