Replace it if it is leaking from the tank, if it is past 12 years and showing rust or noise, or if a repair would cost more than a third of a new unit. Otherwise, fix it and start saving for the replacement.
Replace it if the heat exchanger is cracked, if it is past 15 to 20 years and needs a major part, or if a repair would cost more than a third of a new furnace. Replace a working furnace early only if the efficiency gain is large and you will stay long enough to collect it.
Replace it if the compressor has failed on a unit past 10 years, if it uses R-22 refrigerant and has a leak, or if a repair would cost more than a third of a new system. Replace a capacitor, contactor or fan motor and keep going.
The age you just looked up is the kind of fact that gets lost. A written record of serial numbers, install dates, repairs and who did the work saves the next owner, inspector or insurer from guessing.
A lifetime logbook for the house, organized by system, with room for serial numbers, install dates, repairs and contractors. It stays with the house for the next owner.
Galvanized, polybutylene, cast iron and the sewer line: what fails, what it costs, what insurance won't cover and how to decide.
A buyer's guide to older homes: wiring, pipes, lead, asbestos, insurance refusals and what the repairs actually cost.
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