The expected lifespan of a humidifier-dehumidifier combo can vary depending on the specific model and how well it is maintained. On average, a high-quality humidifier dehumidifier combo unit can last several years with proper care and maintenance. Factors that can impact the lifespan of a combo unit include the frequency of use, the water quality, and the overall quality of the unit. It's important to regularly clean the unit according to the manufacturer's instructions to prevent mineral buildup and other issues that can shorten its lifespan. Choosing a combo unit with high-quality materials and components can also help ensure its longevity.