Summary: I bought 3 HRF14 filters to replace a 24000 in a Honywell 52500 air cleaner. One gasket (a piece of foam included with each filter) was needed. I tried the gasket on the top and bottom of the stack, but it didn't make any difference to the performance of the unit. Assembling the 3 filters and wrapping them with the prefilter is not difficult. The air cleaner seems to be working slightly harder to move the air through the new filters, so it makes a little more noise. The ability to clean the new filters with a standard vacuum instead of replacing them is a big advantage.