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PadMatch / Every humidifier water panel and furnace filter size

Part numberAprilAire 12 vs AprilAire 35
no
AprilAire 12
11.5 in W x 14.75 in H x 1.75 in D
AprilAire 35
10 in W x 13 in H x 1.75 in D
AprilAire 12 fits
AprilAire 112, 224, 225, 440, 445, 445A, 448
AprilAire 35 fits
AprilAire 350, 360, 560, 560A, 568, 600, 600A, 600M, 700, 700A, 700M, 760, 760A, 768

Whether the AprilAire 12 and AprilAire 35 humidifier pads interchange.

Not interchangeable. The AprilAire 12 and AprilAire 35 fit different humidifiers.
Fitment notes

Both are Aprilaire mesh panels but different sizes: the 12 is 14.75 inches high for the 440 and 445 units, the 35 is 13 inches high for the 600 and 700 units. They do not interchange.

The 12 is the tallest Aprilaire panel. If a replacement stands almost 2 inches proud of the frame, you have a 12 in a 600, or a 35 in a 440. Match the humidifier model number.

Find your model

Read the number stamped on the humidifier cabinet or printed on the old pad, then match it below. Confirm the frame size before buying a generic.

Related

Sources: AprilAire Water Panel 12 product page · AprilAire Water Panel 35 product page · AprilAire Water Panel Guide