Product review (5 stars): Carrier Humidifier replacement Filter
Buying this filter online is THE WAY TO GO!
Apparently these replacement filters are not commonly carried in the large national hardware stores, thus your only solution was to pay a furnace contractor to make a home visit to simply replace these filters, an with their huge costs and the giant mark-up they charge, it was crazy. Plus, we have hard water so we need a new filter about twice a year.
I did an internet search and found these filters on AMAZON, and the price was 1/10th the price of a home visit from a contractor!
They were cheap enough that I could buy 5 year's worth of filters for the same price as a single visit/replacement from the heating contractor!
And these are the exact same filters!
They are very easy to install as well.