According to most manufacturer recommendations, you should change the humidifier pad once a year. Nonetheless, it may wear out faster during the winter. For this reason, consider changing it frequently.Failure to replace it will cause you problems, which may include reduced efficiency, clogging of the humidifier drainage, and so on. You need some professional knowledge of humidifiers to change the pad. Otherwise, you could damage your unit. When the need arises, it is best to seek the help of an expert.