Replace once a year?? or when prompted by the service light</br>Simple to replace</br>Includes o-ring</br></br>Product Description</br></br>Aprilaire Canister for the Model 800.?This is the heart of the Aprilaire Model 800 Steam Humidifier.?See your Model 800 owner's manual for replacement instructions.?</br><br/>http://www.amazon.com/gp/product/B0085YQUNY