Troubleshooting guide
Typical ranges, what actually moves them, and the point where repairing stops making sense.
These are the ranges the trade generally works to. Treat them as planning figures, not promises. Individual units routinely beat them or fall well short.
| Equipment | Typical service life | What tends to end it |
|---|---|---|
| Central air conditioner | 12 to 17 years | Compressor failure, refrigerant leaks, coil corrosion |
| Gas furnace | 15 to 20 years | Heat exchanger cracking, control board failure |
| Heat pump | 10 to 15 years | Runs for both heating and cooling, so roughly double the hours |
| Wall or floor furnace | Often 20 or more | Simple, few moving parts, but low efficiency and safety standards have moved on |
Notice the heat pump line. It is not built worse than an air conditioner. It simply does two jobs, so it accumulates run hours roughly twice as fast.
Run hours, not calendar years. This is the one that matters most, and it is why local context beats a national average. A system in the East Bay might run a few weeks of real cooling load a year. The same model in Phoenix runs most of the summer. Fifteen calendar years here is simply not the same amount of wear.
Salt air, if you are near the water. Condenser coils are aluminium and copper sitting outdoors. Close to the Bay, in parts of Alameda and along the shoreline in San Leandro and Oakland, salt accelerates corrosion on those coils and on the cabinet. It is a genuine local factor, and rinsing the outdoor coil with plain water a couple of times a year is a real, free mitigation.
Filter changes. The single cheapest thing that extends equipment life. Restricted airflow makes the furnace overheat and the AC coil freeze, and both stress components that are expensive to replace.
Whether it was sized correctly. An oversized system short cycles, switching on and off repeatedly instead of running steadily. Every start is the hardest moment in a compressor's life, so an oversized unit ages faster while also being less comfortable.
The heuristic most of the trade uses is simple arithmetic: multiply the age of the unit in years by the quoted repair cost. If the result is more than about five thousand, replacement is usually the better spend. A four hundred dollar repair on a six year old unit is clearly worth doing. The same repair on a sixteen year old unit is not, because you are investing in something with little life left.
It is a rule of thumb rather than a law, and it deliberately ignores things that matter to you specifically: how long you plan to stay in the house, whether the repair is a known weak point or a random failure, and whether you would want to change fuel or add cooling anyway.
One local note worth knowing before you decide. Alameda County jurisdictions require a permit for furnace and AC replacement, which brings an inspection of venting and gas connections. That is a real cost and a real timeline, and it is also the reason a quote that quietly omits the permit is not actually cheaper.
FAQ
A central air conditioner typically lasts 12 to 17 years. Systems in mild climates such as the Bay Area often reach the upper end of that, because they accumulate far fewer run hours than the same equipment in a hot inland climate.
A gas furnace generally runs 15 to 20 years. Older wall and floor furnaces, which are common in East Bay housing stock, often exceed that because they are mechanically simple, though they are far less efficient and predate current safety standards.
Usually only if the repair is minor. A common rule of thumb is to multiply the unit's age by the repair cost: if the result is over roughly five thousand, replacement tends to be the better spend. A 15 year old unit needing a compressor is almost always a replacement.
Typically a little less, around 10 to 15 years, but not because it is built worse. A heat pump provides both heating and cooling, so it runs roughly twice as many hours per year as a cooling-only air conditioner.
Change the filter on schedule. Restricted airflow causes the furnace to overheat and the AC evaporator coil to freeze, and both of those stress the expensive components. If you live near the Bay, rinsing the outdoor condenser coil with plain water a couple of times a year is the second best thing, because salt air corrodes it.
Local repair