Honeywell manufacturers the HRF-APP1 air filter for use many with many models of air purifiers. When you open it up, you see that the pre filter is full of white spots or powder. No mention is made of these spots in the instructions or on the box.
What are the white spots on this pre-filter? Are they mold?
No, they're not mold. The white spots are clusters of Zeolite, a mineral with absorbent properties that is commonly used in many commercial products. They are supposed to be on this filter.
When I install the prefilter, white spots on the outside or inside?
Honeywell told me that it does not matter which direction the spots on the filter face.
What's the cheapest place to buy these filters?
Amazon.com has them for $11.99 each. Both Honeywell.com and Home Depot charge $16.95 each. Amazon is certainly a better deal, especially if you are going to buy a whole bunch of them at once.