m Ransley wrote:
Using 5, 1" filters wont work, you wont have enough air pass and will
overheat your furnace and get little air. A 5" media lasts, allows
much less 1st time pollutant pass through. Use what its designed for
a 5" unit.

I built a wooden frame that fit in my 5 inch media slot and which accepted
standard one inch media.

The problem with 5 inch is that it "looks" dirty just as fast as one inch and
nobody will tell you "for certain" how long you should use the filter before
replacing and the HVAC crowd is always warning us about not letting the filter
get too clogged. Well if you don't have a pressure meter how do you tell this?

With a three to five dollar one inch filter I can take the attitude "if in doubt
replace it". That gets pretty expensive with five inch media. The stuff that
came in my furnace was over forty dollars a pop.