You have to evaluate the big picture to see what is most cost effective and practical for you. So instead of a simple answer, I'll pose a lot of questions. What types of parts are failing? Are they parts that you could learn to identify, troubleshoot and replace yourself? Is it the same stuff all the time? Do you own a screwdriver? Is a service/insurance contract available from either your current company or another one in the area? At least you'll have control over your yearly maintenance expenses. Is it worth replacing the systems entirely to gain another 10 years of *free* service contracts. Has the technology improved significantly? Is your current system sized correctly? Shop around. Is it worth continuing with the same type of system? 300% efficient electric heat is great as long as the payback on your upfront investment is shorter than the life expectancy of the equipment. Might a 90+% efficient natural gas system cost less to buy, operate, and maintain over the next 10 years? What about cooling?