No secondary drain line? Float switch installed

Im seeing this more and more on new builds. Theres a float switch installed but the secondary drain is capped. Is this ok. Personally I dont think so, i woukd want both. Any requirements that state either or?

IMO that condensation line should terminate to a drain.

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My understanding is that is OKAY

From IRC:

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 not less than 3/4-inch (19 mm) nominal pipe size. One of the following methods shall be used:

  1. An auxiliary drain pan without a separate drain line shall be installed under the coils on which condensation 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 pan shall be equipped with a fitting to allow for drainage. The auxiliary drain pan shall be constructed in accordance with Item 1 of this section.

Edit: but maybe the secondary drain should have an uncapped nipple leading into the pan, instead of being capped like you said? Ill let others provide input on that.

Edit2: On second reading, that standard does say “the pan should have a fitting to allow for drainage.” That’s referring to the inner pan, huh? looks like you do need a fitting to allow drainage into the aux pan.


There is no requirement to hook up the secondary. There is a requirement to install a float switch or equivalent if there is a drain pan below the unit and it is located above the ceiling in the Attic Etc.

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Float switch is fine.

I just make an informational comment in my report about them so they know if the system shuts down, call an HVAC tech.


I guess you could just unscrew it?

Yep, from what I’ve learned it’s one or the other. To me it’s much more important to be sure the pan is completely under the coils and water will actually reach the drain or switch. In that pic the looks to be separated from the pan and there’s a good chance the condensate will run out before triggering the switch.

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There are two different pans being referred to here, in my understanding.

There’s the pan inside the evap coil, and then there is the aux pan. The aux pan should not have the plug taken off, if it is not drained to the exterior.

The secondary condensate drain on the evap coil unit needs to have the cap taken off, if it is meant to drain into the aux pan… without damaging the evap coil, anyway

I would not refer to the aux pan drain that you just referenced as the “secondary condensate”, necessarily. After all, sometimes there is a secondary condensate drain in addition to the aux pan drain (they are almost always joined at some point, but my point stands)

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OP, you have a picture of the larger area, including the evap coil?

I am not sure what that is.

I know of this

And this:

What do you call the port that has this float switch installed on it?

It’s not the primary…not the tertiary… it’s the……

The primary and secondary condensate drains are directly attached to the interior drain pan below the evaporator coil. Typically, the secondary drain is either elevated vertically above the primary drain or there is a partial plug in the secondary compared to the primary. The auxiliary drain pan and drain are the exterior pan and drain below the hvac unit.


The evaporator coil is not going to get damaged if the secondary is plugged. The coil is usually made of aluminum or copper and is wet during operation anyways. That’s where the condensate(water) comes from in the first place.

If the secondary drain is plugged, the water overflows the internal drain pan and gets soaked up in the insulation and eventually leaks out at joints in the outer metal box surrounding the evaporator coil, and then into the pan below. The metal box will rust but that’s not the main problem. The main problem is the wet insulation holding water and becoming a mold factory. The wet insulation also loses R-value, which is an energy efficiency issue. The outside metal box is also now going to have moisture condense on it, leading to more mold growth on the outside. If the unit is in a crawlspace, it will start activate the mold in the crawlspace. Triple whammy.


That’s the damage I was referring to

The cabinet, not the coil. My bad.

Exactly what I was imagining!

??? Sorry that drain should terminate over a window to help indicate that there is an issue. The float switch is an emergency back up incase the line gets stopped up. That setup is relying on a man made, properly installed, and operating device.

The whole system needs to be properly maintained. The pan’s drain can get clogged just as easily and you won’t see any dripping in front of a window until it’s leaking down the ceiling. The codes, as mentioned, allow the secondary pan not to drain if there is a float kill switch. If you do not agree, the codes need to change. Now, I agree that both would be better than just the switch alone, but it’s not required. Usually, the switch kills the AC and people call a tech to fix the issue, so no problem. The float switch should be tested yearly, just like a low water level cut off on a steam boiler.

If the switch works right. To me it’s just cheapness and laziness, and god forbid should an HVAC tech make a mistake, and they are never cheap and lazy. There’s a better chance that the wonder kill switch wont work than the line clogging up. The line won’t usually clog unless the system has had deferred maintenance for a while.