Houston Attics Often Have Mold From HVAC Condensation
We really shouldn’t put air conditioning air handlers in the attic. It causes several issues, and the majority of homes here have a least a little bit of HVAC sweating. Whether or not it becomes a larger issue depends on several factors.
The video above is in a relatively new house, and the suspected microbial growth on it looks like it’s been building up rapidly. While the homeowner told me it’s “mold,” I usually refer to it as suspected microbial growth – but that’s a topic for a future blog.
What to look for in your attic
If you see condensation (often called “sweating”) on your air handler, that’s a problem. While it’s normal to have a little bit of sweating, it can still drip and cause mold to grow. If you see condensation in several areas around the HVAC system, it could be a much bigger issue than meets the eye.
When there’s liquid water dripping in the attic, it often runs down into the blown-in insulation where it spreads out, saturates all of the insulation that’s touching, and even starts to grow mold on the drywall below.
If the condensation is near your HVAC filter like in this video, that’s especially bad. You never want the inside of your HVAC to have condensation (aside from the condenser coils). The paper filter is a great source of fuel for mold to grow – all it needs is enough moisture.
If the condensation is significant enough to be dripping on the wood platform that the air handler sits on, that’s a big problem. While the wood subfloor is very resistant to dry rotting, it will eventually rot. The bigger problem lies underneath of it, however.
Improperly sealed air handler
If you see gaps in the tape or mastic as shown in this video, that is likely creating additional moisture issues. When the air conditioning is on, cold air may be escaping out of the cracks into the attic, causing condensation. When the AC is off, those cracks are also allowing hot, humid attic air into the air handler. This could even be a bigger problem than cold air escaping.
Other parts of the HVAC system should also be sealed, including the ducts, boots, plenum, and dampers. It’s complicated…but the general idea is you don’t want hot attic air getting into the system, and you also don’t want cold air shooting out into the attic.
Attic insulation wet enough to grow mold
When the HVAC system is sweating, the blown-in insulation throughout the attic should be checked with an invasive moisture meter as shown in the video. You can’t tell if insulation has elevated moisture by touching it. Instead, rely on moisture readings from a quality moisture meter. Generally speaking, 16% moisture content can support mold growth, and 20% moisture content can cause wood to dry rot.
The blown-in insulation is also sitting on the paper-faced side of the ceiling drywall of the room below. The moisture from the insulation eventually causes the ceilings to grow mold and bacteria, so it’s a good idea to start mitigating this problem as soon as you notice it!
If you’re not sure whether your attic has these issues, feel free to fill out the form below for an inspection!
Great point—HVAC condensation is a major but often overlooked cause of attic mold. When an air handler is sweating, that excess moisture can drip into the attic, creating the perfect environment for mold growth and costly mold remediation. Regular maintenance, proper insulation, and ensuring the unit is sized and installed correctly can help prevent these moisture issues before they escalate.
Agreed! Thanks for sharing your thoughts.