I have a white powdery substance collecting on my furnace filter. It is a MERV 5 filter and only lasts about 10 days. There has been no drywall work done for several years. Does any body have any idea what this could be?
If you’re located in a climate where indoor air gets dry in the winter, and there is a humidifier upstream of the filter, the white particles may be mineral deposits left behind by evaporating water. A properly running humidifier should be putting only water vapour into the air, leaving the mineral deposits behind in the unit. A malfunctioning unit may be putting liquid water into the air stream, along with the minerals dissolved in the liquid.
I didn’t know that furnace mounted atomizing type humidifiers were available. I recall we bought one of the standalone types for a single room but we only used it for a short while before we recognized why every horizontal surface in the room was turning white.
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