Please see below to order replacement parts for your P-series purifiers. The Pre-Filter needs to be replaced or washed every 6-12 months depending on the air quality of the installation space. The Cell will run for 2.5 years before it will need to be replaced. These time durations assume 24/7 continuous use. The P-series purifiers include indicator lights that automatically notify the user when to replace the Cell or change the Pre-Filter. It is easy to replace the Pre-Filter and Cell in just a few minutes.