When to Replace Your Furnace and AC, and When to Repair

Replace when the repair is structural, not incidental: a cracked heat exchanger, a failed compressor on a system past its service life, or a refrigerant the market no longer supplies. Repair when the fault is a part and the rest of the system still measures within spec. Age alone decides nothing.

The question of when to replace your furnace and AC usually gets answered by whoever happens to be standing in the attic. That is the problem. A replacement recommendation is a conclusion, and a conclusion needs readings behind it. Here is what we look at on a service visit, and what each finding actually settles.

Start With the Age Bands, Then Stop Leaning on Them

ASHRAE's published median service life is 15 years for a residential single or split package air conditioner, 18 years for a gas fired or oil fired furnace, and 15 years for a residential air to air heat pump. ENERGY STAR puts its "look at replacement" line earlier: more than 10 years for an air conditioner or heat pump, more than 15 for a furnace or boiler.

Those are medians across large samples, not expiration dates. A correctly charged, correctly sized system with a clean return path can run well past the median, and a furnace in a mild Los Angeles winter accumulates far fewer run hours than a national median assumes. An oversized condenser short cycling in an unsealed attic will not reach it. Age tells you which questions to ask. It does not answer them.

So the first step is the nameplate, not the invoice. Manufacture date, refrigerant type, rated capacity, and the model and serial that let us look up the manufacturer's target values. Then we measure against them.

The Findings That End the Decision

A few findings move a system from repairable to finished, and none of them are about age by itself.

A breached heat exchanger. This is a safety call, not an economic one. A furnace that can put combustion products into the supply air comes out of service that day. On a furnace near or past the 18 year band, replacing the exchanger is rarely the right spend even when the part exists.

Compressor failure on a system past its service life. The compressor is the most expensive single component in the condenser, and on a unit that age every other part is the same age. You are buying the most costly piece of a machine that is going to need the rest.

Refrigerant added repeatedly with no leak found and repaired. Topping off a charge is not a repair, it is a subscription. If the leak has been chased for two or three seasons without being located, the coil or the line set is usually telling you something.

Corrosion across the coil slab. Pinhole and formicary leaks spread. One repair on a corroded coil tends to be followed by another in a different spot.

The Findings That Usually Mean Repair

Most of what fails is a part. Capacitors, contactors, igniters, inducer motors, blower motors, control boards, thermostats, condensate pumps. These are components with their own service lives, and replacing one on an otherwise healthy system is maintenance, not life support.

Two findings get misread as death sentences and are usually neither. High total external static pressure is a duct, filter and return problem, so replacing the equipment without fixing it just buys a new blower the same restriction. Low airflow from a dirty blower wheel or a crushed flex run is the same story. Both are common in Los Angeles houses where the duct system is older than the equipment attached to it.

The test is simple. After the part is replaced, do the readings come back inside the manufacturer's range? If they do, the system is not at the end of anything. We wrote about where that line sits in replacement versus optimization.

Refrigerant Is the Variable That Changed

Refrigerant rarely forces a replacement on its own. It changes what a repair costs and how certain it is, and that belongs in the decision instead of in a scare line.

R-22. EPA states that domestic manufacturers may no longer produce new HCFC-22 and importers may no longer import it, and that after 2020 only recycled, reclaimed or previously produced R-22 can be used to service existing equipment. EPA is also explicit that there is no requirement to get a new system or convert an existing one. So an R-22 system can still be fixed. A leak on one is simply a weaker investment than the same leak on a newer machine.

R-410A. Still serviceable, and EPA says plainly that there are no requirements to stop using equipment currently in use. Production is stepping down under the AIM Act, with allowances at 60 percent of baseline for 2024 through 2028 and 15 percent from 2036, so availability thins over time rather than ending on a date.

New equipment. New systems moved to A2L refrigerants such as R-454B. EPA published an amended rule on May 26, 2026, effective July 27, 2026, allowing continued installation of R-410A units manufactured or imported before January 1, 2025 until existing supplies run out. All of that is current as of October 2026 and worth re-checking at quote time.

Why the 50 Percent Rule Fails Here

The common rule of thumb says replace once a repair reaches half of what a new system would cost. It fails in Los Angeles for two reasons.

First, it treats the equipment as the whole system. In most houses we open up, the performance went into duct leakage, a starved return, and a filter housing that lets air around the media. Swapping the box leaves all of that in place.

Second, it ignores sizing. A great deal of what gets replaced here was oversized when it was installed, so a like for like replacement repeats the original mistake at full price. A right sized system sounds too small to most homeowners. That is an objection worth having before the equipment is ordered, not after it is running.

What a Service Visit Should Hand You Before You Decide

Whatever the recommendation, these numbers should be on the paperwork when the technician leaves:

Total external static pressure against the blower's rated maximum. Superheat and subcooling against the manufacturer's target. Temperature split across the coil. Compressor and blower amp draw against nameplate RLA and FLA. A combustion analysis and a heat exchanger inspection on the furnace. Nameplate manufacture date, refrigerant type and rated capacity. Filter condition, filter fit, and the state of the return path.

If a visit ends in a replacement recommendation and none of those readings, the recommendation is a guess wearing a clipboard. That is the whole argument behind what a real tune-up measures.

If You Do Replace, Decide the Scope Once

Furnaces and air conditioners fail on different schedules but share a cabinet, a coil and a duct system. Replacing the condenser alone and leaving a 20 year old furnace, coil and blower behind gives you new equipment running outside the airflow conditions it was rated at, plus a second disruption in a year or two.

When both sides are inside the age bands above, a single changeout to a heat pump covers heating and cooling with one machine and one refrigerant circuit. The reason is precision and control, not virtue. For reference on what new equipment has to meet, the federal regional minimum for split system air conditioners in the Southwest region, which includes California, is 14.3 SEER2 and 11.7 EER2 below 45,000 Btu/h.

On incentives, the federal picture narrowed. The section 25C Energy Efficient Home Improvement Credit is not allowed for property placed in service after December 31, 2025, per the IRS, confirmed October 2026. Utility programs still exist and differ by territory, and the LADWP and Southern California Edison service areas do not offer the same thing. We confirm what applies to a specific address at quote time rather than publishing a figure that moves. If you want to see what a changeout looks like for your house, start at your replacement price.