My family has a conditioned garage with an horizontal furnace hung from the ceiling. I noticed some black material on the plaster that surrounds the ductwork in the garage. I used an infrared camera to see if i could determine if there was a temperature difference in the area. To me the area in question is where the conditioned cool air leaves the handler and enters into the ductwork. My concern is that condensation is forming in this area and could be a potential area for fungal growth. The garage is conditioned and stays around 75 degrees, but a lot of warm air come into the garage daily and likely rises and condenses on the cold area. I do not want to confuse the black material as sealant. I plan to use a moisture meter and will also swab the material and will send it to a lab for analysis. Anybody in SWFL have experience seeing this? I am new to inspecting and the area and am trying to learn as much as possible.
What did you see without the infrared imager?
Yes, John, I saw that pic.
My question was:
I would recommend that you get some training in order to use the IR imager satisfactorily.
Hi Larry,
I see what appears to be a black like material running along the rim of the air handler. I am currently taking Internachis Infrared Course and just need to complete the research assignment and final exam, which is why I posted this. I do agree I need help in terms of calibrating the camera correctly so I can get the correct information from the image. If you have any recommendations to any extra infrared training please let me know. I am just using it as a tool combined with my eyes & moisture meter. Just looking to see if anyone has seen this before and trying to learn as much as possible.
Yes. I see it frequently. It is either mold or fine particulates such as dust/soot.
Generally, in my area, the warm, humid state of GA, it is mold that flourishes on the porous mastic material. This typically occurs in unconditioned spaces with little or no ventilation due to high humidity and surface dew point. Crawlspaces, garages and attics with poor ventilation are frequent offenders.
Seam/air leakage may contribute to the issue.
If you use it on that plenum it will read 99% saturated 100% of the time no matter the moisture content.
A couple from what is available:
The first question to address is: What was the dew point temperature in the garage? Your camera is showing a temperature of 72 degrees Fahrenheit. Is this below the dew point temperature? This is crucial because anytime the temperature goes below the dew point, condensation occurs.
Additionally, it is important to consider the normal operating temperature of the HVAC evaporator. When the evaporator runs at a temperature below the dew point, condensation becomes inevitable.
Concerns About Fungal Growth
Why are you so concerned about fungal growth in the garage? It is not inside the house. However, placing the air conditioner air handler in the garage is not ideal for your geographical location. Unfortunately, this is how the house was constructed.
Issues with Plaster and Moisture Retention
The use of plaster around the air duct connection to the air handler is problematic. Plaster is porous and retains moisture, much like your ceiling. This can exacerbate issues related to condensation and fungal growth.
Observations from Thermal Imaging
The thermal anomaly visible in your thermal image is geometrical and consistent. If you find it bothersome, you can simply wash it off with a cleaning solution like 409.
Mold and Its Origins
It is important to note that mold originates outdoors. The garage is considered an outdoor space, and the air conditioner operates outdoors as well. In your area, the air conditioner produces temperatures below the dew point nearly 100% of the time when it runs due to high humidity levels. This makes condensation and mold growth a persistent occurrence.
Seam/air leakage may contribute to the issue.
Hi Brian,
Thanks so much for the info and your response. Im in Fort Myers FL and it is also very humid here. Will take that into account in regards to the moisture meter.
Thanks so much!
I think the original post is evolving. 
I do not see that anywhere in the post. I should say, air leakage (if present) could contribute to the problem.
Hi David,
Thank you for your response. I recently have read a lot about dew point and am trying to understand it better. You make a great point in how the dew point also contributes to condensation. A lot of stuff is going on in the garage between the AC for the garage, the air handler hung from the ceiling and the hot air that infiltrates in frequently. Thanks for all the info and will continue to learn/investigate.
Morning, John. Hope to find you well.
May wag…Mildew.
To me, the black streaky stains on the tape is mildew on the sealing tape at the airhander transition to the ductwork.
Poorly sealed transition area.
Remedy: Appropriate sealant tape like mastic or mold-resistant foil tape or mastic sealant.
As well, the condensate disposal is suspect.
Have any other images of the furnace and evaporator housing and condensate dispersal lines?
Hi Robert,
Thanks for your response and information. I do not have any other photos of the evaporator housing as I did not dismantle the front cover. I can find where the condensate line starts and ends but did not follow it completely. It either runs through the wall or the attic to the exterior. Will try and get more photos as I investigate. I appreciate you providing insight!
Here in Florida, nearly every AHU in a garage will have that condition on the plenum. Some are much worse that what you have in that photo.
Although I don’t live in Florida, I do remember seeing that condition on several garage AHUs while visiting and helping my brides parents and their friends who wintered down there over the years.
Hi Dominic,
Thanks for the information! Will keep this in mind moving forward.
