Is a service contract a good deal?
We replaced our central AC last year, and the heating/AC company that did the work offered a costly annual service contract that provides annual preventive maintenance.
We have not signed on. In the 17 we've lived in this house, we only occasionally had preventive maintenance done, and have not had any serious problems. We have a natural gas hydronic heating system which means that when the thermstat calls for heat, water from the hot water boiler is pumped into a heat exchange device (I think they're coils), and a fan blows air over the coils thereby heating the air and blowing it into the house. I believe this heat exchange system is also integrated into the AC, but I'm not sure how and what purpose it serves (Is it the condenser?). The system is very good for smaller size homes like ours (1600 square feet), although it is not the most efficient. We avoided the highly efficient gas furnaces (like Trane) (98% efficient) because they tend to dry the air too much, and using a humidifier to compensate for that can be problematic.
My question is: How often should I have a service technician do preventive maintenance on the system?