Pee-ew, My Air Conditioning System Stinks (literally)

lynnie338July 26, 2011

I have a brand new central air conditioning system that was installed in my house last year. My house was built in 1910 and never had air conditioning before. I have a dual A/C system with a high velocity (small duct) system for the second and third floors and a standard Carrier A/C system located in the basement that cools only the first floor.

The basement has stone walls and is unfinished. Some areas of the floor have damp spots. The floor is poured concrete that has not been painted.

I purchased a new A/C filter before I started using the first floor A/C system two weeks ago. When I turned on the first floor A/C, I noticed that the air blowing from the vents makes the first floor smell and feel like the basement- damp and musty.

Before I realized that there might be something wrong with the system, I took a scented gel sheet (lilacs) into the basement to mount onto the A/C filter to get rid of the odor and so that the first floor would smell like lilacs. However, I did not know which side of the filter was the intake/outlet so that I could place the gel sheet correctly. So, I left the gel sheet on a table in the basement next to the A/C/unit (which was on). I went to the second floor of my house to get the A/C instruction manual to identify the intake/outlet, so that I could place the gel sheet on the correct side of the filter.

When I returned to the first floor, the whole floor smelled like lilacs, and I did not even install the gel sheet. Therefore, it seems to me that the A/C unit is drawing air from the basement. I then thought that the A/C unit was supposed to draw air from the outside.

I called the A/C installer and he came to my house. He checked the ductwork in the basement to make sure that it was securely taped at the joints. He could find no openings where basement air would enter the A/C system. I asked him where the outside air intake was for the system. He told me that I have a "closed system" and that air is re-circulated from the first floor through the return vents to the A/C unit and that air is not brought in to the unit from outside. He also said that if air was brought in from the outside, on a very hot day the A/C unit would have to work much harder to cool the air.

Also, the A/C unit does not seem to help dry out the humidity in the basement because the floor has damp spots.

I have two questions:

(1) How is the basement smell getting into my air conditioner?

(2) How do I get my air conditioner to stop sending damp and musty air to my first floor?

Thank you!!

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If you turn off the first floor AC, does the lilac smell migrate to the first floor from your cellar table?

If not, you are right and the installer is wrong. You have a duct leak somewhere that is drawing cellar air into your system. That depressurizes the cellar and pressurizes the first floor. Outside air is then sucked into the cellar and inside air blown out of the first floor area. That seems like way too much air leakage for a new system. It is inefficient at best, but it can cause other problems as well.

Depressurizing an area of the home can be dangerous. It can prevent the exit of combustion fumes from water heaters, boilers and furnaces and fill the house with them. What kind of heat and water heater do you have and where are they located?

If you cellar is cool and outside is humid, drawing in outside air could lead to higher humidity in the cellar if the dew point of the outside air is lower than cellar temperature.

f the system is not supposed to condition the cellar, you should not see much of an effect on humidity down there. What was the cellar humidity like before AC install? You might have to attack this problem separately. Is it warm or cool down there?

Did the same outfit install the second system?

    Bookmark   July 26, 2011 at 2:26PM
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Thanks Ionized.

If I turn off the A/C, I get no smells from the basement. No damp/musty smell and no lilac smell.

I have a tankless water heater and an oil tank for oil heat, both in the basement.

When the installer came to check the problem, he told me that the A/C was supposed to help dry out the basement. The basement is a little cooler than the first floor.

The humidity seems worse than before I installed the A/C. I thought that I might be because I power-washed the basement floor a month ago and the damp spots have not dried even though I ran two portable de-humidifiers for several days afterwards. (There is a french drain around the perimeter that channels water to an exit point out of the house.)

The installer installed both systems. The upstairs system works fine and there are no unusual smells.

    Bookmark   July 26, 2011 at 11:41PM
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The installer is making no sense if you are relaying the information correctly. If the AC is supposed to be helping to dry the basement, you will get air mixed into the first floor air. Yet he checks for leaks in the cellar ducts. Small leaks would be of little importance if there are intentional ducts openings there to intentionally circulate drying air.

It sounds like you have a moisture problem in the cellar that should be addressed. If hot, humid air from outside is being drawn in by your new AC, it cold be making the humidity problem worse.

Can you check to see if air is being drawn in through the water heater or chimney when the AC blower is running?

    Bookmark   July 27, 2011 at 2:11PM
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Make sure your condensation line has a trap in it. I don't know where you are draining it to but if it is draining to a basement drain, if there is no trap it could pull air from the basement into the system

    Bookmark   July 27, 2011 at 2:22PM
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I understand. Now then, I don't see how the basement could get dry if there are no openings in the ductwork in the basement. I will ask the installer to clarify.

I will check tonight to see if air is being drawn in through the water heater or chimney when the A/C blower is running.

My condensate line is a small pvc pipe that drains into an open French drain in one corner of the basement. I do not know if there is a trap. But that is certainly something to check, especially since the pipe ends at the most damp and odorous corner of the basement.

    Bookmark   July 27, 2011 at 4:41PM
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The drain should be positive, shouldn't it?

    Bookmark   July 27, 2011 at 9:34PM
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I checked for a trap. There is a j-shaped pipe leading out of the condenser unit and the drain is directed positive (downhill) until it gets to the floor, then it is flat until it gets to the drain opening in the floor, when it is positive again.

I ran the A/C with a lighted incense stick at the end of the drain pipe and the smoke from the incense stick did not get drawn into the drain pipe.

I did find that there is a section of bellows-like material that is stapled closed and air might be getting in there. I also found that when I placed the incense stick at the top of the condenser unit, the smoke blew around alot and I could feel an air current

    Bookmark   August 2, 2011 at 9:49AM
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This thread is from 2011. It EXACTLY describes to a tee my situation. Wondering, if Lynnie338 is still on GW, if there was a resolution?

I'm desperate!

    Bookmark   September 21, 2014 at 12:55PM
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