How do I find out my furnace's AFUE rating?

Check the yellow EnergyGuide label on the unit itself — it's usually affixed to the side or front of the cabinet. If the label is missing, look up the model number on the manufacturer's website or ask your HVAC technician to look it up during a service visit. Furnaces manufactured before roughly 2006 often lack this label entirely, which is itself a sign the unit predates modern efficiency standards.

Can a furnace be repaired if the heat exchanger is cracked?

Technically yes — heat exchangers can sometimes be replaced as a standalone part — but it's rarely the right financial decision. A replacement heat exchanger for a mid-range furnace can cost $500 to $1,500 in parts alone, plus labor, and it doesn't address the age or condition of the rest of the system. Most HVAC professionals will recommend full furnace replacement when a cracked heat exchanger is confirmed, and that's generally sound advice.

Is it worth repairing a furnace right before selling a house?

It depends on what buyers in your market expect and how the repair affects the inspection report. A non-functional furnace will almost certainly come up in a home inspection and give buyers leverage to negotiate the price down — often more than the repair would cost. A minor repair that restores function is usually worth doing before listing. A major repair on an old system is a judgment call: some sellers disclose the issue and adjust the price rather than invest in a system the new owner may replace anyway.

What is a typical furnace lifespan, and how do I know where mine falls?

Most gas furnaces are designed for 15 to 20 years of service life, though maintenance history has a significant effect on where in that range any individual unit lands. To find your furnace's age, locate the serial number on the data plate (usually inside the cabinet door) and look it up on the manufacturer's website — most encode the manufacture date in the serial number. If the unit is past 15 years and has had limited maintenance, treat it as being near end of life regardless of whether it's currently running.

Furnace Repair or Replace? The 50% Rule and Other Ways To Decide

The simplest rule of thumb in the heating industry goes like this: if the cost to repair your furnace exceeds 50% of what a new one would cost, replace it. That’s the 50% rule, and it’s a solid starting point — but it’s not the whole picture. A furnace’s age, efficiency rating, repair history, and the comfort problems it’s causing all factor into a decision that can easily run $3,000 to $6,000 or more either way. This post walks through every variable so you can make the call with confidence, not guesswork.

What the 50% Rule Actually Means

The 50% rule isn’t about the sticker price of a repair in isolation. It’s a ratio: repair cost ÷ replacement cost. If a new furnace installed in your home would run roughly $4,000, then any single repair over $2,000 tips the math toward replacement.

Why does the ratio matter more than the dollar amount alone? Because a furnace that needs a $1,800 heat exchanger today may need a $900 inducer motor next winter and a $600 igniter the winter after that. Older systems tend to fail in clusters — one component wears out, and the stress of compensating for it accelerates wear on the next. The 50% rule is really a proxy for asking: am I patching a system that’s already in decline?

The rule works best when you also know the furnace’s age. Most gas furnaces are designed for a service life of 15 to 20 years. A $1,500 repair on a 6-year-old furnace is almost always worth it. The same repair on a 17-year-old unit is a much harder sell — you’re investing in a system that may have only a few heating seasons left regardless.

Other Factors That Tip the Decision

Age and repair cost are the big two, but several other signals matter:

Efficiency rating (AFUE) Furnaces manufactured before the mid-2000s commonly run at 60–70% AFUE (Annual Fuel Utilization Efficiency). Today’s standard units are 80% AFUE; high-efficiency condensing furnaces reach 95–98%. In Southern California, where heating seasons are shorter than in colder climates, the payback period on a high-efficiency upgrade is longer than it would be in, say, Minnesota — but Southern California Gas rates still make efficiency worth calculating. If your current furnace is below 80% AFUE and you’re paying to repair it, you’re also paying to run an inefficient system every month it stays in service.

Repair frequency One repair in five years is normal. Two or three repairs in a single season is a pattern. Keep a simple log of what’s been fixed and when. If you’re calling for service more than once a year, the cumulative repair cost is probably outpacing the value the system is delivering.

Comfort and airflow problems Uneven heating — one room cold, another stuffy — can mean a failing blower motor, a cracked heat exchanger, or simply a system that’s undersized for the home as it exists today (additions, sealed windows, changed insulation all shift the load). A furnace that can’t keep up isn’t just annoying; it’s working harder than it should, which accelerates wear.

Carbon monoxide history or cracked heat exchanger This one is non-negotiable: a confirmed cracked heat exchanger means replacement, full stop. A cracked heat exchanger allows combustion gases — including carbon monoxide — to mix with the air circulating through your home. Patching a cracked heat exchanger is rarely a lasting fix, and the part itself often costs more than 50% of a new unit anyway.

R-22 or older refrigerant (if the system is a heat pump) If you’re evaluating a heat pump rather than a gas furnace, check the refrigerant type. R-22 (Freon) has been phased out, and remaining supplies are expensive. A heat pump still running on R-22 that needs a refrigerant-related repair is almost always a replacement candidate.

How to Get a Repair Estimate You Can Actually Use

Before you can apply the 50% rule, you need two numbers: what the repair costs and what replacement costs. Here’s how to get both without wasting time:

Get the repair diagnosis in writing. A good technician will tell you exactly what part failed, why it failed, and whether any related components show wear. Ask specifically: Is this the only issue, or are there other parts that are marginal? A technician who has inspected the full system can tell you whether this repair is likely to be a one-time fix or the beginning of a series.
Ask for a replacement quote at the same visit. Most HVAC companies will give you a side-by-side comparison. If they won’t, that’s useful information too.
Factor in rebates. Southern California Gas and some local utilities periodically offer rebates on high-efficiency furnace installations. These can meaningfully shift the replacement cost downward. Ask your contractor which rebates are currently active before you decide.
Consider financing. A repair might cost less today, but replacement may be financeable at a monthly payment that’s easier to manage than an unexpected emergency repair bill.

What NOT to Do When Your Furnace Breaks Down

Don’t run a gas oven or range to heat the house. It’s a carbon monoxide risk and a fire hazard.
Don’t ignore a yellow or orange burner flame. A healthy gas flame is blue. Yellow or orange can indicate incomplete combustion and a potential CO issue. Shut the system off and call for service.
Don’t approve a repair before you know the full diagnosis. Replacing an igniter when the real problem is a failing control board just delays the inevitable — and you’ll pay twice.
Don’t assume the cheapest repair is the right repair. Sometimes it is. Sometimes a technician recommending a $200 fix on a 19-year-old furnace is doing you a disservice by not telling you the whole picture.
Don’t skip the second opinion on a major repair. If a repair quote is over $1,000 and your furnace is more than 12 years old, a second opinion costs you very little and could save you from a bad decision in either direction.

When Replacement Makes Clear Sense

Stop running the numbers and move toward replacement when any of these are true:

The furnace is 18 years old or older and has needed more than one repair in the past two years.
A cracked heat exchanger has been diagnosed.
The repair quote exceeds 50% of replacement cost and the unit is past the midpoint of its expected life.
The system was undersized or poorly matched to the home from the start — no amount of repair fixes a fundamental sizing problem.
You’re planning a home addition, significant insulation upgrade, or window replacement. A load calculation after those changes may show the existing system can’t serve the updated envelope anyway.

Making the Call

Most homeowners facing a furnace breakdown are doing it in January, when the system stops working and the house is already cold. That’s not the ideal moment for a calm cost-benefit analysis, but it’s the moment most people actually face it.

If you’re in Corona or the surrounding Inland Empire area and you’re not sure whether a repair or replacement makes more sense for your specific system, RT Olson Plumbing, Heating and Air Conditioning can walk you through the diagnosis and give you honest numbers for both paths. Call (951) 344-5596 to schedule a furnace inspection or get a replacement quote — the goal is to give you the information you need to decide, not to push you toward the more expensive option.