Traps on Primary Condensate lines

[Scott Dana]

I found several threads dealing with this but I didn't find any definitive answer to the question of whether primary condensate lines need traps. If they do, why? I somehow remember someone telling me that it was required only of Heat Pumps. But again, if so, why? Hoping you guys can set me straight. Thanks.

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[Scott Patterson]

I found several threads dealing with this but I didn't find any definitive answer to the question of whether primary condensate lines need traps. If they do, why? I somehow remember someone telling me that it was required only of Heat Pumps. But again, if so, why? Hoping you guys can set me straight. Thanks.

Yes, they are required. By code and the manufacturers.

The trap will help keep air and other stuff from being sucked into the evaporator.

[Scott Dana]

Required only for Heat Pumps? That's almost always where I see them.

And how could something be sucked into the evaporator coil? I just want to have the answer when some asks "Why" after I call this out in a report. Thanks.

[John Arnold]

Not sucked inside the coil line itself with the refrigerant, but sucked into the air handler where the evaporator coil sits. So, for instance, if the condensate line discharges somewhere smelly, nasty odors could be sucked into the air handler and distributed throughout the house.

[Scott Dana]

OK, sounds unlikely but I get the point. But can someone please site what these traps are needed on? Heat Pumps only? Is there a code reference that can be sited? Thanks.

[John Arnold]

I can't think of any reason why it would be heat pumps only. The difference between a heat pump being run in AC mode, and an AC unit being run in AC mode has nothing to do with condensate removal.
I don't have a code reference. Try looking up some manufacturer's installation guides on the web?

[Rick Yerger]

if the condensate drain line is under negative pressure e.g. upstream of the blower (behind the blower) a condensate drain is needed. the way in understand this is if air is being "pulled" through the A coil it requires a trap, if air is being pushed through the coil, it does not.

[Scott Dana]

OK, I spoke to a local HVAC guy and here is what he said. A trap is needed on any system that does not have a flue. I'm not sure I understood completely why as he was telling me this from within a hot attic, but it was something about how the air handler pulls air in instead of pushing air out. Something along those lines. But basically if it has a flue, it would NOT need a trap. If anyone can clarify that would be great.

[John Arnold]

I found this by searching the archive.

M304.8.2 SEAL. The condensate drain system shall provide a seal that
prevents ingestion of air or other gas, through the condensate drip pan
drain and overflow connections, from all outside sources, including the
condensate disposal place, during all operating conditions.
Source Standard Mechanical Code 1994

M304.8.2 SEAL. The condensate drain system shall provide a seal that
prevents ingestion of air or other gas, through the condensate drip pan
drain and overflow connections, from all outside sources, including the
condensate disposal place.
Source Standard Mechanical Code 1997

[Jim Luttrall]

Scott, basically the trap seal prevents air from moving through the drain line. If you don't have a trap, then you can move conditioned air out of the system (bad for energy use) or dirty air into the system (bad for your health).
All openings in the ductwork should be sealed to prevent energy loss. You would not think of leaving a 3/4 inch hole in a duct un-sealed. Why would a 3/4 inch hole in the drain pipe be different?
While this is a general standard, I don't think it would be much of a stretch to use
IRC 2003 section
N1102.1.10 Air leakage All joints, seams, penetrations; site-built windows, doors, and skylights; openings between window and door assemblies and their respective jambs and framing; and other sources of air leakage (infiltration and exfiltration) through the building thermal envelope shall be caulked, gasketed, weather stripped, wrapped , or otherwise sealed to limit incontrolled air movement.
Jim

[Jerry Peck]

if the condensate drain line is under negative pressure e.g. upstream of the blower (behind the blower) a condensate drain is needed. the way in understand this is if air is being "pulled" through the A coil it requires a trap, if air is being pushed through the coil, it does not.

Almost right ...

BOTH require traps.

Not only do you NOT want to suck unconditioned air in through the condensate line, but you DO NOT want to blow conditioned air out through the condensate line.

[Jerry Peck]

OK, I spoke to a local HVAC guy and here is what he said. A trap is needed on any system that does not have a flue.

He is (I presume) assuming that any system which does not have a flue has a coil, however, many systems have both a coil and a flue.

If you have a coil through which refrigerant runs, you will need a trap.

[Rick Yerger]

Almost right ...

BOTH require traps.

Not only do you NOT want to suck unconditioned air in through the condensate line, but you DO NOT want to blow conditioned air out through the condensate line.

How does air blow through a condensate drain if it is located behind the blower?, The key words are under negative pressure, if the system is running air could not blow out of a condensate drain because air is traveling, under pressure, the oposite direction.

[Joe Nernberg]

This fella removed the trap and vent. Maybe this hairy knuckle-dragger thought the condensate would drain faster.

[Jim Luttrall]

Rick, I won't presume to speak for Jerry, but I think the point is that negative or positive air flow through a line is not right; air leakage is air leakage. There are both types of systems out there, the coil on the upstream or downstream.

[Michael Greenwalt]

The biggest culprit I find is with high efficiency units. The manufacture instructions require (in most cases I would say but haven't found one so far that hasn't required it) that the cooling condensate line be trapped before it reaches the heating condensate line if they drain to a common pipe. Generally (check unit specifics) the heat condensate is internally trapped (usually visible internally right before the condensate line protrudes through the housing). Most installers do not trap the cooling condensate line prior to reaching the common drian union.
Now, do not ask me why, I have read the reasons but went over my head. (or through it, or around it)

[Jerry Peck]

Rick, I won't presume to speak for Jerry, but I think the point is that negative or positive air flow through a line is not right; air leakage is air leakage. There are both types of systems out there, the coil on the upstream or downstream.

Precisely.

EITHER will cause air flow through the condensate line.

One causes air flow to flow into the unit unfiltered and bringing with it whatever was in the air wherever it came from.

One causes air to flow out of the unit, losing air which has already been conditioned, thereby wasting that energy.

That is why BOTH types require traps. On BOTH primary and secondary condensate lines.

[Jim Luttrall]

Even though it is not as apparent, the air leakage into the air stream is also a net loss of energy. This will cause pressurization of the building envelope and tiny losses at each door, window or other penetration.
Leakage should be controlled at every point in the system.

[Rick Yerger]

Precisely.

EITHER will cause air flow through the condensate line.

One causes air flow to flow into the unit unfiltered and bringing with it whatever was in the air wherever it came from.

One causes air to flow out of the unit, losing air which has already been conditioned, thereby wasting that energy.

That is why BOTH types require traps. On BOTH primary and secondary condensate lines.

I See your points, I'm thinking of a split system a/c with the coil borrowing the blower of the furnace. I can see with a heat pump system a trap is essential for the reason mentioned.

[James Duffin]

Don't all split systems share the same blower?

[Bruce King]

Another reason and a very important one on the condensate lines that suck air is due to the water being splashed all over the coil if a trap is not present.

This causes the moisture to be blown right back into the house.

[Michael Thomas]

Scott,

This is the best article I've seen on condensate trapping problems, it used to be on the Trane AC site, but is no longer on-line (that I can find, anyway).

I used to print these pages when explaining trapping issues and really missed this material, so a few months back I retrieved the pages and diagrams from the Wayback Machine net archives and assembled them into a single document for future reference - it's also available as an editable .doc file which is too big for upload here. If anyone would like a copy let me know at mdt@pargoninspects.com.

[Jerry Peck]

Micheal,

Very good information. Brought up issues I had not even thought of before.

Thank you.

[Jim Luttrall]

Good information Michael, thanks!

[Scott Dana]

Thanks Michael. Proof as to the benefit of this website!

[Mike Huppi]

In a lot of newer furnaces the drain lines go into a small box on the sides of the interior of the furnace and then to the visible drain line, I am assuming that this is being considered a trap or a built in trap. So are these traps.

[David R2]

1. To think of why traps are necessary, think of how air flows when the device is powered off or not operating. Air can flow in both directions.

Then, when it is operating, air can still flow in both directions. (The fact that air is far more likely to flow in one of the two directions is not relevant.)

2. Most of the unusual situations described in the pdf document linked to above, are normal concerns in planning drain plumbing. (Traps too deep, air gap from slope not consistent, etc). Knowing drain plumbing helps.

David

[Thom Walker]

Thanks for the info Michael.

[Scott Dana]

OK, two more condensate line questions (yes, I am fixated on these right now). I would think the combination of the two primary lines shown here would not be recommended in case the line gets clogged somehow. Agreed?

Also, is there a code for how primary condensate lines should be terminated? Out on inspections I see some going to the ground like you see in the pic, while others are elbowed downward a foot or so off the ground.

[Jerry Peck]

From the IRC. (bold is mine)

- M1411.3 Condensate disposal.

Condensate from all cooling coils or evaporators shall be conveyed from the drain pan outlet to an approved place of disposal. Condensate shall not discharge into a street, alley or other areas where it would cause a nuisance.

That *could* be read several ways ... *the way* *I* read it is that the condensate from all coils, each individually, shall be drained from the pan outlet to the place of disposal, not to another condensate line, *and then* to the place of disposal.

Another way it could be read is ... that the condensate from all coils, all coils combined together, shall be drained from the pan outlet to the place of disposal, not to another condensate line, *and then* to the place of disposal.

Of course, though, in reading it that way, *all coils* would have to be located above *one large condensate pan* as the code clearly states "from the drain pan outlet to an approved place of disposal".

That second reading, even though different from my reading of it, still does not have condensate lines connected together.

[Martin lehman]

Rick Yerger?? I think I saw you on HGTV's House Detective. You're a pretty funny guy - great episode. Most of the time the inspectors are pretty dry.
Are you out here in CA?