HVAC and duct mold in Macon homes

Air conditioning is a dehumidifier that happens to also cool the air. Warm indoor air passes across an evaporator coil that is well below the dew point, moisture condenses on the fins, and the resulting water runs into a drain pan and out through a condensate line. In a Macon August the system can pull a startling amount of water out of the air over the course of a day.

That is by design and it is fine, right up until the water stops leaving.

Where it goes wrong

• The condensate line clogs. Biological growth builds up inside the drain line until water backs up into the pan and over the edge. This is the single most common HVAC water failure in the Southeast.
• The drain pan corrodes. Older galvanised pans rust through and drip onto whatever is below — a closet floor, a ceiling, or the crawl space framing.
• The coil stays wet and dirty. A coil coated in dust holds moisture between cycles, and dust is organic. Growth on the coil sits directly in the airstream.
• Ducts sweat. Duct runs through a hot attic or a humid crawl space with damaged or compressed insulation drop below dew point on the outside, and condensation forms on the exterior of the duct.
• The system is oversized. Short cycles cool the air without running long enough to dehumidify it, leaving the whole house at a relative humidity that supports growth.
• Return leaks. A return duct or plenum that draws air from a crawl space or attic rather than from inside the house is pulling humid, spore-laden air directly into the system.

Signs it is the system rather than the room

The pattern usually gives it away. The smell is worst in the first minutes after the blower starts. It is present in several rooms at once rather than one. It is strongest at the supply registers. Sometimes there is visible growth on the register grilles themselves, or dark speckling on the ceiling around them where humid air is condensing on cool drywall.

What the work involves

It is genuinely two trades, and honest contractors say so. The remediation side handles cleaning and containment — HEPA vacuuming and treating the coil, blower wheel, plenum and accessible duct interior, and removing duct that is lined with porous insulation which has become contaminated and cannot be properly cleaned. The HVAC side handles the mechanical faults: clearing or replacing the condensate line, fitting a float switch, replacing a corroded pan, repairing duct insulation, sealing leaks, and addressing sizing or run-time problems.

Doing the first without the second is the HVAC equivalent of remediating a wall without fixing the roof.

Keeping it from coming back

• Have the condensate line cleared as routine seasonal maintenance before cooling season, not after it backs up.
• Fit a float switch that shuts the system down when the pan fills, if there is not one already.
• Change filters on schedule and use a filter the system is actually designed for — an overly restrictive filter can cause its own coil problems.
• Keep the return path clean and sealed so the system is drawing air from inside the house.
• Watch run times. A system that satisfies the thermostat in very short bursts through July is probably not dehumidifying properly.