Thread: Missing secondary drain lines

These are air handlers equipped with AC coils, which are located in a crawl space area with a concrete floor. Is a secondary drain line and trap required on these units. The HVAC company does not seem to think so.

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County just issued the CO

"Is a secondary drain line and trap required on these units"
Yes, but there is an alternative available.

From 2006 IRC

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.

M1411.3.1 Auxiliary and secondary drain systems.

In
addition to the requirements of Section M1411.3, a secondary
drain or auxiliary drain pan shall be required for each
cooling or evaporator coil where damage to any building
components will occur as a result of overflow from the
equipment drain pan or stoppage in the condensate drain
piping. Such piping shall maintain a minimum horizontal
slope in the direction of discharge of not less than 1/8 unit
vertical in 12 units horizontal (1-percent slope). Drain piping
shall be a minimum of 3/4-inch (19 mm) nominal pipe
size. One of the following methods shall be used:
1. An auxiliary drain pan with a separate drain shall be
installed under the coils on which condensation will
occur. The auxiliary pan drain shall discharge to a
conspicuous point of disposal to alert occupants in the
event of a stoppage of the primary drain. The pan shall
have a minimum depth of 1.5 inches (38 mm), shall
not be less than 3 inches (76 mm) larger than the unit
or the coil dimensions in width and length and shall be
constructed of corrosion-resistant material. Metallic
pans shall have a minimum thickness of not less than
0.0276-inch (0.7 mm) galvanized sheet metal. Nonmetallic
pans shall have a minimum thickness of not
less than 0.0625 inch (1.6 mm).
2. A separate overflow drain line shall be connected to
the drain pan provided with the equipment. This overflow
drain shall discharge to a conspicuous point of
disposal to alert occupants in the event of a stoppage
of the primary drain. The overflow drain line shall
connect to the drain pan at a higher level than the primary
drain connection.
3. An auxiliary drain pan without a separate drain line
shall be installed under the coils on which condensate
will occur. This pan shall be equipped with a water
level detection device conforming to UL 508 that will
shut off the equipment served prior to overflow of the
pan. The auxiliary drain pan shall be constructed in
accordance with Item 1 of this section.
4. A water level detection device conforming to UL 508
shall be provided that will shut off the equipment
served in the event that the primary drain is blocked.
The device shall be installed in the primary drain line,
the overflow drain line or the equipment-supplied
drain pan, located at a point higher than the primary
drain line connection and below the overflow rim of
such pan.

Originally Posted by mathew stouffer

County just issued the CO

I would tell my client (in writing) that even though it was passed by the AHJ there is still a problem. The problem is that if the main condensate drains gets blocked then the condensate is going to run into the unit and duct work. This will cause the unit and/or duct work to rust prematurely and shorten the life of the system. It can also cause mold to grow inside the duct work and create an indoor air quality issue. If the HVAC contractor says you are wrong then ask him where the condensate will go when the main drain gets stopped up? I'll bet you a dollar he will fix it.

In
addition to the requirements of Section M1411.3, a secondary
drain or auxiliary drain pan shall be required for each
cooling or evaporator coil where damage to any building
components will occur as a result of overflow from the
equipment drain pan or stoppage in the condensate drain
piping.

I don't think you can get there from here.
The damage would likely be to the unit, not the basement floor unless there is moisture sensitive building materials on the floor.
However, most manufacturer's require a secondary drain; which would then be a code requirement.

I had one a few weeks ago like that. And no, it didnt have a "water level detection device" installed.

But hey, I guess the new buyers even get the kitchen sink. Visible in photo.

The HVAC companies never think a trap or secondary has to be installed. I wouldn't put much faith in what they claim. I've yet to read a unit install manual that doesn't require a trap install. The secondary drain install wording in some of the install brochures is a little more wishy-washy though. Some say it must be installed, some ramble on and make it a suggestion.
I always right up the lack of traps. If the unit is in the basement and the primary drain is good, I suggest verifying the secondary (kind of wishy-washy) If the unit is in an attic or living space closet, I right up to install it.
Sometimes I can find the install manual for a particular unit other times not.

Based on the limited information in the first photos, and the wider view of the last photo (from a different inspection) I believe this must be brought up:

The PRIMARY condensate drain line REQUIRES a proper trap, and by "proper trap" I mean a trap which meets the configuration shown in the installation instructions, most of which show a 2" water seal, some of which show a 3" water seal, a few which show a 4" water seal, and one type I've now seen 2-3 of which require a 5" water seal. And there there are those which show a 2" water seal and state the requirements on how to determine the trap configuration based on the static pressure within the unit (which is what they are all based on anyway).

The SECONDARY condensate drain line ... SHOULD be installed but is not REQUIRED if the exception is met with the water level detection device - I completely disagree with that, unless an anti-freeze switch is installed too (and HVAC contractors typically never install those unless directed to) ... I believe that code section was the code committee being bent over backward by the contractors lobby and ignoring the homeowners lobby (there really is none) complaining about all the overflowing units ... ... Oh well, that is just another pet peeve of mine.

Given that a air handler is in a crawlspace and that there is a concrete floor below it does NOT mean the overflowing condensate cannot, will not, damage any building component. Otherwise there would not be any requirement for not allowing moisture to drain into the crawlspace - what difference is there of draining condensate to the crawlspace (not allowed) or of draining the overflow condensate to the crawlspace? ESPECIALLY with a concrete floor where the water will not soak into the ground, but will stand there as an ever increasing size pool of water.

I like that last photo in that, you know the phrase "everything but the kitchen sink" and the HVAC contractor threw everything he could at that installation trying to get it correct ... INCLUDING the "kitchen sink".

I've got a collection of photos I've taken over the years of corroded HVAC equipment caused by missing/incorrect/ill-maintained condensate drains.

If I cannot located a manufacturer's prohibition or recommendation against a questionable practice, I insert whichever corrosion picture matches the condition I discovered next to the picture depicting it, and let the client decide if that's a risk they wish to run.

All he has to say is wet switch and he's covered.

Mathew, I am in your area and recently I took a class with 10 other experienced HI's. The consensus was that 98% of condensate drains don't have a trap in them, this doesn't make it right and I still write up every one I see. How's biz.

'All he has to say is wet switch and he's covered."

Maybe I am misinterpreting this post, but a "wet" switch isnt a replacement for a trap in the primary condensate line.


What am I missing?????

This is one of the biggest items I write up around here. I wish the manufactures put it in bold print Trap or no trap. Secondary or no Secondary. I get so much flack from new and old homes from the builders and hvac installers. Most of the time they say the unit doesn't operate properly if the secondary has a trap or the stand pipe before the trap needs to be open not capped. Or It's in the crawl space so it's not required.

Originally Posted by imported_John Smith

'All he has to say is wet switch and he's covered."

Maybe I am misinterpreting this post, but a "wet" switch isnt a replacement for a trap in the primary condensate line.


What am I missing?????

Hi John

As far as I am concerned it is a replacement form a trap onm a secondary. There is no need for a trap past a float switch or the float switch won't work.

If you have a float switch on the secondary the unit shuts down when the water backs up in the unit and it alerts the occupants that the system needs servicing.

The picture below is one I did today with the evap coil over the gas heating unit. No float switch and the water flows over the heat exchanger. Also in this situation and close quarters it is extremely difficult to put a main and secondary drain and trap and vent and and and and

Sorry but the pic load failed. I have to shrink it but I am sure you know what I mean.

Also I have seen every type of system with a main and secondary drain line have a trap on them. Heast Pumps, gas units, electric units.....alll had water flowing thru the primary at a steady pace with no hic ups. They say some set ups will just have the blow blowing around and around and never come out the line. I for one after seeing every set up ther is will tell you that a trap and vent on both the main and secondary works and works well. Thos without just blow a serious amount of conditioned air into the attic or where ever the unit is mounted.

I write up every home I see when there is air blowing out of the main and secondary....new or existing home. It cost literally a few bucks per unit while the units are being installed to save a fortune over time. Also....why does every freaking unit I inspect have air blowing out all around the unit. Do the HVAC guys installing just do not care or what. No offence to those who seal the units. God bless you

OK...so...I am ranting. This is one of my pet peeves.

Ted that is the second issue that is found on the majority of homes. Why can't they seal the coil box to the stinking air handler.

Note my reply said "PRIMARY". I understand the float in regards to the secondary. Maybe Jerry can weigh in on something I havent considered.


"Maybe I am misinterpreting this post, but a "wet" switch isnt a replacement for a trap in the primary condensate line.


What am I missing?????"

Around here condo installations seem to be the worst, often with no pan, no traps, and both lines just stuck down a drain.

When I see them, I ask clients if they want to continue paying to air condition the city sewer lines.

Originally Posted by imported_John Smith

'All he has to say is wet switch and he's covered."

Maybe I am misinterpreting this post, but a "wet" switch isnt a replacement for a trap in the primary condensate line.


What am I missing?????

The water level shut off switch (they are simply float switches in those devices) are allowed in the primary condensate lines under given conditions, and, as you stated, the shut off switch *is not* a substitute for a trap - the trap is still required.

While the shut off switch in the primary condensate line is allowed, to me it is simply a stupid idea, even if the HVAC installers install an anti-freeze switch, but at least an anti-freeze switch would make the use of a shut off switch in the primary condensate line easier to accept.

It is *rare* to find that an anti-freeze switch has been installed, which makes installing the shut off switch in the primary condensate drain line one of the dumbest, stupidest, wackiest, bassackward things the code allows. (Did I control myself enough there? )

I know this is an old thread but I ran into this lack of a secondary drain this morning. I see all the verbage about a water switch, trap, etc.

But....the basic question I have is if there is no seconday drain, and the main drain backs up, how does the water find it's way in the pan when there is no secondary drain line installed. See my photo from this morning.

My point is, it does not have an easy path to the drain pan and backs up inside the coil until gravity finds a way for the water to get out.

Originally Posted by Gene South

My point is, it does not have an easy path to the drain pan and backs up inside the coil until gravity finds a way for the water to get out.

Hence the reason the pan must be 3" larger than the coil cabinet. Remember we are talking minimum requirements.

Originally Posted by Gene South

My point is, it does not have an easy path to the drain pan and backs up inside the coil until gravity finds a way for the water to get out.

The secondary drain should be installed, it could just drain to the auxiliary drain pan.

As yours is set up, the interior pan will overflow into the bottom of the unit, the insulation on the bottom of the unit will become saturated with the water and become useless, the water then continues on and runs out every opening, hole, joint, etc., that it can.

Now, the insulation on the bottom of the AHU needs to be replaced, and it is quite possible that the insulation on the sides of the AHU also need to be replaced. All because there was no secondary drain line to the auxiliary drain pan.

My understanding is when a pan fills inside the unit it can also get water blow by. Water actually blown or drawn into the ducts.

Originally Posted by Mike Schulz

My understanding is when a pan fills inside the unit it can also get water blow by. Water actually blown or drawn into the ducts.

Yes, that too.

What I was pointing out is something a lot of a/c service technicians miss (or ignore) when responding to water overflowing into the auxiliary drain pan and the unit shuts down - they do not do anything with the now-ruined insulation inside the unit.

Maybe I missed this, but if you have a secondary drain line that is trapped, the trap has to have liquid in it to block air flow, right? As long as the primary is draining, how is any water going to get into the secondary trap?

Correct. I always recommend priming the trap with mineral oil or a similar non-toxic to prevent dry traps due evaporation.

Originally Posted by Jim Luttrall

Correct. I always recommend priming the trap with mineral oil or a similar non-toxic to prevent dry traps due evaporation.

Thanks, although I may recommend extra virgin olive oil.

Originally Posted by John Arnold

Maybe I missed this, but if you have a secondary drain line that is trapped, the trap has to have liquid in it to block air flow, right? As long as the primary is draining, how is any water going to get into the secondary trap?

By priming it with liquid.

When the secondary is primed with water, yes, the water will evaporate, so one could use glycerin or mineral oil (which does not evaporate, at least not very fast, it would take years and years) and the water would flow out through the trap past the mineral oil, etc.

How many do prime the trap with mineral oil? Probably very few.

How many prime the trap with water? Probably very few.

Which means that the secondary traps are, most likely, open to allow air to go through.

Then again, how many do everything else they should do? Probably very few.

How many do that other stuff correctly? Even fewer.

The 3 pictures that Matt has shown indicate a coil on the negative air pressure side of the air handler. Secondary drains on these units typically clog before the primary due to the smaller opening at the pan( secondary drains usually are 1/2 the opening of primary at the pan). In basement conditions, a moister alarm or pan switch is preferable to a secondary drain that may mask a drainage issue for some time. Trap switches have proved to work well to prevent damage if they are wired to shut the system down by breaking R on the low voltage side. I would be more concerned of the lack of insulation on the suction line as a probable water issue.