Quote:
Originally Posted by Michael G.
My carrier unit is going on 2 years and I have a 4" filter.
Munn's says replace every 12 months.
We also have to remember our ventilation systems run very little in the winter months
to dirty any filter unless there's a pet in the house.
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I use a Merv 11 filter and replace it every 6 months. Even if the filter is not dirty, the filter material can deteriorate.