Attic furnace with abandoned secondary drain/overflow pan with float switch on primary cond. line

How would you guys and gals comment on this? Seems like the secondary drain line & overflow pan were abandoned after previous issues and a float switch was installed on the primary line.

  1. is this sufficient overflow protection? it seems like the same amount most closet units have.

  2. would you comment on the corrosion in overflow pan & disconnected drain line if it’s apparently no longer being used?

thanks everyone!

My speculation would be that it was more than likely damaged. It still needs to be there, so recommend having it corrected.


im curious - is there any way for condensation to make it into the secondary line/pan if there is a float switch directly on the primary line?

Leak in the drain pan, partial clog, dirty filter causing the a-coil to freeze, ETC… Water will find the path of least resistance.


The reason for the pan is to catch other leaks that can develope. Sometimes condensation can drip from the cabinet into the pan. If that happens, it’s just going to flow out the broken pipe.


yes, thank you

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AHRI’s Fundamentals says, “Even if the condensate drain pan is empty, any signs of prior spill-over should be investigated.” How does that float where it’s placed, if I understand it–the connection on the right-side in photo–, do anything if the primary drain pipe is clogged and there’s no water in it to begin with?

In the likely case the main drain line in a poorly maintained unit like that will clog up, the call seems pretty straightforward inasmuch as the internal drain pan’s auxiliary drain (on the left), as well as the drain from the external, secondary attic pan, will both drain directly to the floor because of the disconnected pipe. As someone pointed out, if the coil ices up from a clogged filter and drips all over the place, the water’s going straight onto the attic floor and into the ceiling below.


Yes. If there is an airflow problem (in A/C) water will flood the interior of the unit.

The switch on the primary drain detects if the pipe is blocked downstream. It does not do anything happening upstream.

The secondary drain is not needed, but the auxiliary pan below the unit must be piped if an auxiliary pan float switch is not installed. I don’t see one anywhere. There is something at the top edge of the pan with wire going to it, but it doesn’t look like it has a pan float inside the pan.

If it wasn’t broken, yes.

Yes. It is still being used. But also note it is not wet at the time (but will be sometime down the road).

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Thank you. My coursework is coming back to me. I was thinking there would only be a condensation leak in the enclosure once both lines were backed up, as a third back-up measure.