The answer to 'when to replace ductless system' is that ductless mini-split systems typically last 10-15 years with proper maintenance. However, there are several factors that can impact the lifespan of a ductless system, including the quality of the equipment, frequency of use, and how well it's maintained.
Some common signs that it may be time to replace a ductless system include reduced cooling/heating performance, increased energy bills, frequent breakdowns, and excessive wear and tear on the components. If your ductless system is over 10 years old and experiencing any of these issues, it's a good idea to have a professional HVAC technician evaluate it to determine if replacement is necessary.