BestAir A12W Replacement Water Pad for Aprilaire models 11.375? x 14.75? x 1.625?. Uses up to 50% less water than a standard metal pad. Surface treated with Micro Free? Anti-Microbial Coating to protect against contaminants and bacteria. Water Pads are crafted to generate higher output and stronger absorption. Paper Design with metal support; Replace at least twice per season; Waterpad that fits: Aprilaire 112 136 224 440 445 445A 448 (12); Chippewa 224 225 226; Humid-Aire Neptune; Walton 600 620 660