The $5,000 rule, and what it is worth
You will find this everywhere: multiply the age of the equipment by the cost of the repair, and if the answer exceeds $5,000, replace it. A fifteen year old system facing a $400 repair scores 6,000, so the rule says replace.
It is a useful prompt and a poor decision-maker. It knows nothing about what actually failed, whether the rest of the equipment is sound, or whether the repair is a wear item or a symptom of something larger. We would rather look at the system.
What actually matters
What failed
This is the single biggest factor. A capacitor, contactor or fan motor is a wear item. A compressor, a leaking evaporator coil or a cracked heat exchanger changes the conversation, because those are expensive and often signal the equipment is near the end.
The repair history
One fault is a repair. A pattern across recent seasons is information about what the next few years will look like.
The condition of everything else
Fixing one component on equipment where several others are visibly tired buys you a short reprieve.
The cost comparison
When a repair starts approaching a meaningful share of replacement cost on equipment with significant age, the maths shifts. Not at a fixed percentage, because it depends on how much life the repair realistically buys.
Problems that were never solved
If the system never heated or cooled the house properly, replacing like for like will disappoint you. That is usually sizing or ductwork, and it is worth establishing first.
What about age on its own?
People start asking somewhere past ten to fifteen years. A well maintained system can run considerably longer, and a neglected one can fail much sooner. Age tells you when to start paying attention, not what to do.
Where we stand
“If a repair will get you through the season, we will tell you, even when a new system is the bigger sale.”
Replacement is worth far more to us than a repair. That is precisely why the commitment is worth making, and why you should expect us to explain the repair option when there is one.
Common questions
What is the $5,000 rule for air conditioners?
Multiply the equipment's age by the repair cost, and if the result exceeds $5,000 the rule says replace. It is a conversation starter. It knows nothing about what actually failed or the condition of the rest of the system.
What is the average life of a house furnace?
Most residential furnaces are considered to be at the older end somewhere past fifteen years, though maintenance and use change that a great deal in both directions.
Is it worth repairing a 15 year old AC?
Often yes, if the failure is a wear item and the rest of the equipment is sound. Much less so if the compressor or evaporator coil has failed.
Should I replace before it fails?
There is a reasonable case if the equipment is well past its useful life and you would rather choose the timing. There is no case for replacing equipment that is working properly because of its age alone.
Reviewed and updated September 2026. Prices shown are owner supplied typical ranges, confirmed after an assessment. If anything here looks out of date, call (615) 400-4993 and tell us.