A/C condensate floor drain backing up

My A/C unit is in the basement and the condensate drains into a floor drain. The drain is very unadorned, it is just a hole in the concrete. I suspect this drains into the sump; I don’t know where else it could go.

  1. Does this drain into the sump?

I also have a portable dehumidifier in the basement and have a hose from that to the same floor drain. It seems like if condensate can go in from one source, it could go in from another.

  1. Is there anything wrong with doing this?

This drain has started to back up occasionally. I do not know if this is because there is a clog (if it is just a hole to the sump, I don’t know how it could possibly be clogged), or if the sump is overflowing (is this the only spot where it would overflow? The sump pump seems to be working so this doesn’t make much sense either). I suction it out with a wet vac (maybe 1-2 quarts of water) and things seem to be fine for a while until it happens again.

I have turned off the dehumidifier to reduce the water until I figure out what’s going on. This first happened years ago and when I suctioned out the drain I got debris that made it look like a clog (dead mouse; wooden disk) but now it is happening more often.

  1. I want to call in a professional. Do I need an A/C tech, or a plumber?

ETA: The drain is underneath the air return ductwork leading to the A/C unit with 2-4" of clearance. I can fit a hose into it but it is hard to reach and removing the ductwork to access it more easily would be a job.

I’d try pouring a cup of bleach down the drain to kill any algae. If you want to go all out to prevent recurrence, go ahead and get some of those algaecide tablets.

I have the exact same setup. I’ve been draining the dehumidifier into the same drain as the AC to no ill effects.

In my basement at least, the drain hole is there for the slop tub. The slop tub also drains into the hole, and my washing machine drains into the slop tub.

Therefore as far as I know the drain is for waste water and not storm water. If it was for storm water I’d be pumping laundry soap into my yard!

So, do you have a slop tub in the basement? Where does it drain to?

And …you can get dye to put in the drain and see if it comes in to the sump crock.

I would call a plumber about the drain. Once you’re to the condensation exiting, the AC guy isn’t involved.

I had something that looked similar: a plain floor drain under the HVAC units and the HVAC condensate was piped towards the opening via flexible tubing. The humidistat overflow and the water heater emergency overflow lines also led to the same floor drain the same way.

But, that drain was plumbed with 4" PVC into the whole house waste water system that led out to the septic tank.

The only way for the OP to know for sure where it goes is to feed a plumbing camera down it and see.

(I’m both a licensed plumber and HVAC tech)

Sounds like the drain needs to be cleared. If the evaporator is draining, I agree its a plumbing issue. In my experience, it’s not pumped to the sump, but rather your main drain.

If nothing else in the house is backing up, I’d suspect the trap at that local floor drain.

I had a drain specialty company come in. They snaked the drain and found some gunk but did not find a major clog. I was not here when they came so I didn’t get to ask questions, but I tend to agree it probably drains into the sewer line. Nothing else is backing up, although it’s the lowest drain in the house. There are no other floor drains in the basement.

Hopefully this is resolved, but it’s happened so often that I am going to have to replace some carpeting and probably some baseboard.

Hooray for your fix.

IME A/C condensate seems to love to grow mold or other mysterious bio-goop.

You might find that dumping a half-cup of laundry bleach down there every couple months pays dividends. It’s certainly cheap insurance. That wouldn’t be real helpful to your septic tank biota if you had a tank, but you’ve said you’re on a sewer system.

I have a condensate trap on the line out of the A/C unit and it seems to be designed for mysterious goop to build up; it has a float valve to shut off the A/C and a brush to clear the trap out. But condensate should be practically like distilled water, shouldn’t it? Where does that brown crap come from?

Yup, Fairfax County sewer.

Thanks again!

Probably algae. (Cough…post #2…cough)

Junk that collects on the pipe. It is wet and mold and other junk will grow on it.

Better get that looked at. Are you allergic to algae?