Our home AC system allows us to put a filter either in the ceiling intake or directly under the air handler intake. I feel the ceiling intake may be better because more debris will be trapped before it gets into the air return duct work. Is a filter at the ceiling intake or the air handler intake location better?

We have been using an 18x30 filter in our ceiling intake, but the filters keep getting bent and sucked into the intake. The actual intake hole measures 18x30 and the filters are 17.5x29.5 and they just don’t fit very snug. We seem to remember when we originally moved into the house it had a filter that was 18.5 x 30.5, but that does not seem to be a standard filter size. Is 18.5 x 30.5 a standard size?

I was thinking get a cheap cut-to-fit "blue" filter to catch the large debris at the ceiling intake to solve our size issue and use a better quality filter at the air handler intake to catch the smaller particles. Is this double filtering too much air flow restriction?

  • As a general statement: if the filter is getting sucked in (as opposed to perhaps getting a little deformed in the middle), then your filter is probably too restrictive for your particular installation or it is poorly constructed. What brand / type of filter are you using? I used to use 3M Filtrete 1000 (the red ones) but found them too restrictive, so switched to the 3M Filtrete 600 (the less-common green ones) and had better results.
    – JimMSDN
    Sep 27, 2020 at 12:19

1 Answer 1


There is no advantage of one location over the other, it's all the same air moving through.

Generally there is a bracket or sometimes just a steel rod that is jammed across the opening to prevent the filter from getting sucked in. Maybe yours got lost along the way? Mine did, so I just bought a piece of steel rod and cut it larger than the opening so that I wedge it in diagonally to hold the filter in.

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