I notice that during this cold winter at Edmonton that my gas furnace filters contain a larger amount of a whitish colored ash on the cold air return side of the filter. I would like to know where this ash is coming from. The air quality in the house seems fine so I cannot see how the ash is coming from the cold air returns. Could the ash indicate a leak in the heat exchanger?

My gas furnaces are mid efficiency ICG Ultimate II (17 years old)

Regards,

Michael Brady

What you call ask could be anything. Is your dryer in the same room as the furnace?

No, the dryer is in a separate room. I think I might know what it is. It may be accumulated calcium carbonate blowing off the screen of the flow-through humidifier when it is dry. The humidifier is attached and blows into the cold air return. Does this make sense?

I would send a sample to a testing company if you really want to know what it is.