There are several variables that determine how long your HME will last. Your pressure setting, how often you use the HME, and how you store it. It is recommended that the HME is stored in an airtight container/zip lock bag when not in use to help it last longer. The estimated time is 7-30 days depending upon the variables listed above. If you feel it is not providing enough humidity, it is time to replace the HME.