The GeneralAire 4123 is the correct replacement filter for the following air cleaner models:
The GeneralAire GA104 MERV 8 Filter Media Cartridge is a replacement air filter for the GeneralAire AC24 and Aprilaire 2140 air cleaner models. This replacement filter media cartridge features a MERV 8 rating for reducing airborne contaminants and particles from your air. The MERV 8 filter measures 15 5/8" x 27 5/8" x 3 3/4" and will improve your overall indoor air quality. The GA104 replacement filter is made from durable construction material and is meant to be a long lasting filtration device.
GeneralAire GA104 MERV 8 Filter Media Cartridge specifications: