Do all A/C condensate lines need a P-trap?

[rgile]

Been looking at some posts around here and notice a lot of mention of P-traps for A/C condensate lines. I have a forced air furnace/air handler in my basement with a standard A/C unit (condenser out side / A/C coil in the main supply truck about a couple inches over the furnace/air handler. The condensate line comes out of the main trunk and runs to the floor just above the drain near the furnace. No p-trap. This is the way it was installed when the house was built (2003). Is this a problem? The line is clear and I can see the condensate stream down when the A/C is running. I've also had to replace it once because it was getting full of some black nasty stuff and it was hard to see if it was flowing or not. So I just changed it.

[airtight_tech]

I wouldn't say they are necessary to a systems operation. They just help keep the condensate lines from getting plugged. If the line is trapped and vented it is also easier to treat with cleaner during preventive maint

[heating_seattle]

They are necessary for proper operation if the coil is on the return side (which most air handlers are). If the coil is under positive pressure its not needed. Inspectors here are retards and want them trapped either way, they also want furnaces double trapped because they dont know their a$$ from a hole in the ground.

[skippedover]

They are necessary for proper operation if the coil is on the return side (which most air handlers are). If the coil is under positive pressure its not needed. Inspectors here are retards and want them trapped either way, they also want furnaces double trapped because they dont know their a$$ from a hole in the ground.

::DD: Double trapping anything will cause the drain to not work. High efficiency gas furnaces all have an internal trap. Highlight that information in the install manual and rub the manual on the nose of the inspector.

[jayar031409]

it depends on the design of your unit. sometimes line without p trap can affect your motor compressor if your motor compressor installed above condensing unit.

[Airmechanical]

yes, in general, all condensate lines need 1 trap


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[bmathews]

it depends on the design of your unit. sometimes line without p trap can affect your motor compressor if your motor compressor installed above condensing unit.

I am curious how a p-trap on an a/c condensate line can affect the motor or compressor?

[salv97]

there needed not for the working part of the furnace,for the gasses during the winter when your running your furnace,since that condensate line goes directly into the sewer line,the trap protects you from gasses being breathed in during the winter

[Airmechanical]

there needed not for the working part of the furnace

for the gasses during the winter when your running your furnace,since that condensate line goes directly into the sewer line

the trap protects you from gasses being breathed in during the winter


ok, so what happens when the trap dries up



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[Rhizzlebop]

Air, thats a good question. In the Southeast, our winters are so short, and even then we have speradic days where we'll need cooling in December sometimes that I bet our traps never dry out.

Up north, I'm sure they run dry, so I dunno how furnaces handle that. Well, maybe they are always on the negative side, so they are under suction, If they indirect drain, then they'd be sucked room air in, just like your return is sucking room air in, so it wouldn't be an issue right?

To te OP, in general, when the condensate line is on the return side of the fan, its under suction. Its like sucking through a straw. If the line is small enough and the suction is high enough, then it'll hold the water in the line just as you can suck through a straw and hold water up from a cup.

The trap has a vertical offset that must be greater than the suction force of the unit. So, if your unit has 1" of negative suction, then the vertical offset must be greater than 1". That means, even with the air sucking the straw, it can't pull the water high enough to offset the drain-out end of the trap, and so the water will flow.

Most residential units only have about 2 or 3 tenths of an inch on the return side so its usually not a big issue there. On bigger units where the suction cna be 2 or 3 inches, it can make a huge difference. If the trap isn't right, it'll fill the drain pan and pour over the sides, before it'll run down the drain line thats clear and open.

[monkeyspanners]

Lots of mini split systems won't drain if they have a trap in the condensate line.

[trey3121]

The new Trane a/h will not require p-traps. In our area you cannot tie the condensate line into the sewer system anyway.

[energy star]

The new Trane a/h will not require p-traps. In our area you cannot tie the condensate line into the sewer system anyway.

If you read the instruction booklet, all units need a trap. Also, the trap is not their to hold back sewer gases anyway.

[trey3121]

If you read the instruction booklet, all units need a trap. Also, the trap is not their to hold back sewer gases anyway.

On a positive pressure system other than loosing minimal air out the condensate line what other reason.

[b26440510]

from what I've read condensate lines should never be drained directly into sewer lines. If they can be installed there they must be installed upstream of a trap.

From what I've been able to gather, a p trap on a positive pressure system is there only to prevent cool air from escaping the system and may be considered optional, but consensus is to install on negative and positive pressure systems.

[Airmechanical]

from what I've read condensate lines should never be drained directly into sewer lines

it's a common sense issue

yes, you should NOT drain hvac stuff into sewage lines

mostly to avoid sewage gas entering the HVAC system



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[airtight_tech]

So does that mean that if the line drains to outside and not a sewer (95% of installs where I am), you don't need a trap? And how is a motor affected (and its location) by a drain that rids a coil of excess condensation???

[airtight_tech]

Lol lil late needed to refresh my phone.
I thought it was cause we just don't have many basements in CA that I never see em drain to sewers but it makes sense why you shouldnt

[Airmechanical]

So does that mean that if the line drains to outside and not a sewer (95% of installs where I am), you don't need a trap?

no that's not right!



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[Rhizzlebop]

Airtight, read my explaination below.

[ICanHas]

Some units have a trap built in, for example Rheem package units. (see #11 in illustration)

You can check it by running the system until its draining water, then feeling for air with your hand or using an incense to see if smoke sucks in. If there is no flow it has one built-in.

Of course, just like bathroom sink trap, nasty things accumulate in the stagnant water, so I don't personally like traps built into the unit that can't be easily cleaned.

On a negative pressure system, especially a package unit, if you don't use a trap, dust kicked up by the condenser fan and landscaping activity gets into your system and ultimately inside your house. On a positive pressure system, its like having a 1" hole in the supply duct that vents cooled air into your garage/outside. I suppose it's not a big deal though, since during heating seasons, the trap will dry out, but since its in the supply path, heated air will escape.

[tinknocker service tech]

simple answer to the op question
read the instalation manul.
If it tell you to install a trap then you install it.
It will also tell you where the best lacation for the trap would be but that isnt eaged in stone real world dictates where the trap can go

if the book says trap not needed then it isnt needed