Mould and Condensation
What causes condensation around AC diffusers?
Water forming at or around a diffuser indicates that surfaces are reaching the temperature at which moisture in the air condenses.
What is happening
Condensation forms when a surface is cold enough relative to the moisture content of the surrounding air. Around diffusers, cold supply air meets humid room air at the grille face and adjacent ceiling.
Contributing factors
High indoor humidity, low supply-air temperature, air leakage around the diffuser, insulation condition in the ceiling void and the introduction of untreated outdoor air can all contribute.
Why it should not be ignored
Persistent damp around a diffuser affects ceiling finishes and can lead to staining and recurring growth on nearby surfaces.
The approach
An assessment establishes measured humidity, surface conditions and the behaviour of the ventilation and AC systems. Reducing indoor moisture with independent humidity control addresses the underlying condition; mechanical and insulation issues are addressed separately.
Technical note: Final equipment selection and expected performance depend on site conditions, system design, outdoor-air conditions and professional assessment.
Related reading
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Mould and Condensation
Why does mould return after cleaning and repainting?
Cleaning removes what is visible on the surface. If the conditions that allowed growth remain, the same surfaces stay at risk.
Humidity Basics
Why is my home humid while the AC is running?
Air-conditioning is designed primarily to control temperature. Moisture removal is a by-product of cooling and varies with conditions.