The Model 558 has been eliminated. The Model 550 is still part of the Aprilaire lineup. The company's first recirculating bypass humidifier was the Model 225, later replaced by the 445. Both were ...

"In the early 1990s, the flagships of the Aprilaire line were Models 550 and 560 bypass humidifiers. These models featured compression-molded, glass-filled polyester plastic housings and represented ...