The Aprilaire 4021 is the correct replacement for the following humidifiers:
The Aprilaire 4021 Humidifier Orifice is a tiny red nylon component that allows a specific amount of water to enter your humidifier. Some of the water will evaporate and some performs the important flushing action. This process will keep the water panel clean while reducing maintenance to a minimum. Also known as part number 4021, the Aprilaire humidifier orifice is a unique fit for the Aprilaire 112 and 224 humidifier models. The Aprilaire brand is also identified by the following spelling variations: April Aire, April Air or Aprilair.
Aprilaire Red Orifice specifications:
The Aprilaire orifice could become clogged with mineral deposits and sediments, such as rust and scale. For optimum performance of your Aprilaire Humidifier, replace your orifice annually, based on usage and water quality. Disconnect the power and shut off your water supply before servicing. 120 volts could cause serious injury from electrical shock. Don't forget to clean or replace your inline strainer when you replace your orifice.