What's the oily discharge coming from our central air and heat?!

December 4, 2008 8:20 AM

Our central AC/Heating system leaked some kind of, uh, oil (!?) last night. I have no idea what it is, the super is baffled. More inside.

My wife and I have been living in our current apartment for about 6 months now. It has central air and heat, ducts upstairs and downstairs, and those ducts are covered with sheet rock or drywall- Something to obscure them and make them mesh with the walls.

We've had no problems with the AC and while the heat is INCREDIBLY HOT and dry, we've had no problems using it for the last 6 weeks or so.

Last night my wife noticed what looked like water damage spreading in a maybe 6x6 inch circle. I was concerned, so I got up on a ladder and wiped it up. To my surprise it was NOT water. It was slightly oily and had a faint odor. It reminds me of mechanical lubricant. It's a clear liquid and it had collected in a couple of fat drops within the circle, but none had dripped on the table below.

I wiped it up and aside from a very hard to see oil stain underneath the duct, there hasn't been any other leakage.

As far as I know, our heat is gas, not oil. We are on the first floor, but no one above us has had any issues.

We're flummoxed, the super is flummoxed, I was hoping MeFi might have some suggestions. As of this morning no more of the, uh, discharge had collected in that spot despite our running the heat on and off all night.

Thoughts?

posted by GilloD to home & garden (6 comments total)

It might be propylene glycol or some other anti-freeze type fluid. My HVAC system, although ultimately ducted hot air, heats up glycol that is run through pipes to the air handlers in the basement and attic, exchanging the heated fluid with heated air. I had a leak shortly after the system was put on-line.

In large quantities it'll be a pinkish fluid but in a small puddle it might look clear. It's probably mixed with water as well, further diluting the color.
posted by bondcliff at 8:38 AM on December 4, 2008

Should we be concerned?
posted by GilloD at 8:40 AM on December 4, 2008

If it's Glycol, it's just alcohol. We're told it's "food grade", though I wouldn't go drinking it. Personally I'd be concerned about any leak but I don't think you have to worry about your short-term health. (I am not your...) Glycol is just a guess anyway, based on the fact that it's coming from an HVAC system.

I think the concern about any leak in the home is not with what you can see, but with what you can't see.
posted by bondcliff at 8:47 AM on December 4, 2008

I think you could have a potentially serious problem with your heating system.

I agree with bondcliff that it's probably some kind of heat exchanger fluid, but as I understand your question, it sounds like it is leaking from one of your ducts into a ceiling far from the actual heater--and above it.

That means the leak you are seeing is not a drip from a pool of liquid that came out of the heater as a liquid, but is liquid condensed from a vapor and leaking from a joint in one of the ducts.

This in turn would imply that your heater is somehow boiling the heat exchanger fluid and sending it into the duct work as a vapor. It could be doing that as a result of a leak in the exchanger piping allowing fluid to drip onto a hot element, or because the fluid in the exchanger is getting so hot the pressure in the exchanger piping is building up to a point that a relief valve opens and blows off some vapor.

Because your "heat is INCREDIBLY HOT and dry", I would say the latter, but in any case you should get a qualified service tech in there as soon as you can.

By the way, I would imagine you could see some of the exchanger fluid as a film on the inside of your windows, if they are single glazed.
posted by jamjam at 9:48 AM on December 4, 2008

It's probably oil from the AC compressor. A typical AC unit uses R-134a as a refrigerant and that will evaporate at ambient conditions, so it's unlikely to be a heat exchange fluid. Call a service tech. I'll wager you'll need to have the compressor replaced.
posted by electroboy at 10:21 AM on December 4, 2008

Via Follow-up: Our super said it was a bit of excess sealant from the ducts, probably melting under the heat. It hasn't happened since, so I'm not sure if that's correct or not, but it doesn't seem to be a recurring problem.
posted by GilloD at 10:40 AM on January 5