AC Smells Like Feet when on, coils clean and draining, techs can’t figure it out
Before I start, I’ll say I have done some homework on the internet regarding this common odor problem. None of the common solutions seem to apply (except possibly dirty ductwork, but its a newer system?). Tech has been out twice and has assured me of the following: Drain pan is clean and draining, condensate pump is working and lines are not plugged, coils are clean and recently recoated.
The system was installed November 2021. New American Standard 2 stage gas fired furnace, new ductwork, new Aprilaire 8100 ERV (ducted into return), new 2 stage A/C. We replaced a boiler system so everything was new.
One story house, 2000sf, system/ductwork is located in the basement. Basement is semi-conditioned. Climate zone 5A.
I have a dehumidifier in the basement keeping it around 50%. Upstairs humidity is less controlled, varies with the outdoor conditions. We rely mostly on the AC to keep humidity down.
I have replaced the filter 3x in the last month trying to fix it. It does not seem to help. We are have an Aprilaire 2210 filter box and are using OEM Merv 13 filters. The smell does seem to not exist in the return side though and only exists forward of the coils/blower.
The smell comes from all floor vents, so its not like something dropped in one of the vents. Typically, if the system is off for a while (half day or more), it will kick on for 5-10 min without a smell, then the smell starts 5-10min in and continues if it cycles on and off often.
Any thoughts, advice or expertise would be appreciated. At this point the HVAC techs are just cleaning/replacing to rule things out on our dime and they are at a loss. Their current recommendation is to clean and sanitize the ductwork, but it seems weird in such a new system. The smell has been occurring this entire cooling season, did not have any smells during heating season or last year’s cooling season. I’d also like to know whats causing it to avoid this happening again.
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Replies
Sounds like “dirty socks syndrome”
It is most important to be 100% sure the side of your evaporator coil where the return air enters is clean. Often this side of the coil is difficult or imposable to see without cutting a new hole in the ductwork.
Is their a trap on the drain line without a deep enough trap the blower could pull in air from the pluming vent IE sewer gas.
https://phyxter.ai/blog/dirty-sock-syndrome
Walta
"ERV (ducted into return)"
I think this is where your problem is. If this is like 99% of installs, the furnace fan is interlocked with the ERV. Because of this, during cooling season, the furnace fan will continue to run when the AC cycles off which causes the condensate on the coil to re-evaporate. Along with the moisture you get the dirty sock smell.
Simple test is to turn off the ERV (also make sure your thermostat is set NOT to run the furnace fan all the time) and see if the smell is gone.
If this fixes it, you need better controls for the ERV.