Change the school building’s air filter every 2 months

After exactly 2 months, the hospital-grade furnace filter in our school building was caked with dust. (Happily, it was changed this week, on 2/9/23.)

Old filter on the bottom; new one on top, for comparison.
(As usual, click/tap on an image to enlarge it.)

So this is a brief note just to say: Hooray for routine maintenance! 👏