What Age Actually Tells You
Equipment age is one data point. It tells you roughly where the system sits on its expected lifespan curve. According to the Department of Energy, furnaces typically last 15-20 years and air conditioners last 15-20 years. Heat pumps, which work year-round, tend to die earlier, around 10-15 years.
But averages aren't predictions. They're what happens when you combine the systems that fail at 8 years with the ones that last until 30.
The 1991 furnace in that colonial? The homeowner had a binder with every service record since 1993. Annual tune-ups. Two heat exchanger inspections. New inducer motor in 2011. New blower motor in 2018. That furnace was better documented than most used cars.
I looked at the heat exchanger with my inspection camera. No cracks. No rust. Combustion appeared clean. The burners looked like they could go another decade with proper care.
"This thing's been babied," I told him. "I can't guarantee how long it will last, but it's in better shape than a lot of 10-year-old furnaces I see."
My Brother-in-Law's Expensive Lesson
Rick bought a house three years ago with an 8-year-old furnace and AC. Practically new by my standards. No service records, but the previous owner said it worked fine.
Within 18 months, the AC compressor failed. $2,800 to replace. Six months after that, the furnace inducer motor died. Another $600. Then the heat exchanger cracked. $1,800 for the part alone, plus the technician recommended replacing the whole furnace because of the labor involved.
"I thought newer meant better," Rick said. "I didn't even think to ask about maintenance."
The previous owners had never serviced anything. They ran the system until something broke, fixed it with the cheapest option, and sold the house before the next thing failed. Rick inherited years of deferred maintenance disguised as a "newer" system.
What Rick Missed
Looking back, there were signs. The furnace filter was caked with years of grime. The condenser coils looked like they'd never been cleaned. The condensate drain was partially clogged. The supply registers had layers of dust that suggested infrequent filter changes.
These are things an inspector notes, but they're also things you can check yourself. Clean systems with service records are likely to keep running. Dirty systems with no maintenance history are gambling with someone else's chips.
The Repair vs. Replace Question
Here's the framework I use when clients ask whether to repair or replace an aging system.
The 50% Rule
If the repair costs more than 50% of replacement and the system is over 10 years old, replacement usually makes more sense. You're putting a lot of money into something with limited remaining life.
Example: A 14-year-old AC needs a new compressor. Compressor replacement is $2,500. New AC installed is $5,500. At 45% of replacement cost, you could go either way. But that compressor is going into a system with 14-year-old coils, contactors, and capacitors. What fails next?
If the same compressor fails at 6 years old, the math changes. The rest of the system has another decade of life, probably. Fix it.
The Efficiency Argument
Old HVAC equipment is less efficient than new equipment. A furnace from 1995 probably runs at 80% AFUE (Annual Fuel Utilization Efficiency). A new high-efficiency unit runs at 95-98% AFUE. That's 15-18% less fuel for the same heat output.
The same logic applies to air conditioners. Old units might be 8-10 SEER (Seasonal Energy Efficiency Ratio). Current minimum standards require 14-15 SEER. High-efficiency units hit 20+ SEER.
But efficiency savings don't always justify early replacement. In mild climates with low utility costs, the payback period can exceed the equipment's lifespan. Run the numbers for your situation before assuming new is better.
The Refrigerant Issue
Here's one that actually does force replacement timing: R-22 refrigerant.
Air conditioners made before 2010 likely use R-22 (also called Freon). The U.S. phased out R-22 production in 2020. The refrigerant that's still available is recycled from old systems, and prices have gone through the roof.
My friend Carol has a 2003 AC unit that developed a slow refrigerant leak last summer. The HVAC technician quoted $150 per pound for R-22, and her system needed about 6 pounds. That's $900 in refrigerant alone, plus $400 for the leak repair, for a 21-year-old air conditioner.
She replaced the whole system instead. The new one uses R-410A, which is widely available and reasonably priced. It also dropped her summer electric bills by about $40 a month.
When to Get Ahead of Failure
Emergency replacements cost more. When your furnace dies on a January Sunday, you're not shopping around. You're paying whatever the first available contractor charges to get heat back before your pipes freeze.
I tell clients with 15+ year systems to start getting quotes proactively. Not because they have to replace right now, but because having numbers in hand changes the dynamic.
The Planning Window
When a system is 15-18 years old and working fine, that's the time to get three quotes. Learn what replacement costs in your area. Ask about equipment options. Find a contractor you trust.
Then when the system does need a major repair, you can make an informed decision. Spend $1,200 to fix the blower motor, or apply that money toward the $7,000 replacement you already know is coming?
Contractors also offer better deals when you're not in a rush. Spring and fall are the slow seasons. Summer emergency calls and winter panic replacements are the profit centers. Timing matters.
What Quotes Should Include
When getting HVAC replacement quotes, make sure each one specifies:
- Equipment brand and model numbers
- SEER rating (AC) and AFUE rating (furnace)
- What's included (thermostat, pad, disconnect, line set, permits)
- Warranty terms for parts and labor
- Removal and disposal of old equipment
- Timeline for installation
Compare apples to apples. A quote for an 18 SEER unit isn't comparable to one for a 14 SEER unit, even if the second one is cheaper.
Real Numbers From Recent Replacements
I asked around my network for recent HVAC replacement costs. Here's what people actually paid in 2024:
Furnace Only
My neighbor Dave replaced his 22-year-old furnace last October. 80,000 BTU, 96% AFUE, mid-range brand. Total installed cost: $4,200 including a new thermostat.
My client Jennifer went high-end. Variable-speed blower, modulating gas valve, premium brand. She paid $6,800.
The cheapest I've heard of recently was $2,900 for a builder-grade 80% AFUE unit with basic installation. You get what you pay for, but sometimes basic is enough.
AC Only
AC replacement ranges from about $4,000 for a 14 SEER unit to $8,000+ for high-efficiency systems with variable-speed compressors.
Carol's replacement that I mentioned earlier was $5,400 for a 16 SEER unit. That included new refrigerant lines, electrical disconnect, and concrete pad.
Complete System
Furnace and AC together typically runs $6,000-15,000 depending on efficiency level, brand, and installation complexity.
A standard mid-efficiency system in a straightforward installation: $7,000-9,000. High-efficiency with premium features: $12,000-15,000. Budget installations with basic equipment: $5,500-7,000.
These are rough guidelines for my area. Prices vary significantly by region, contractor, and current demand.
What I'd Do
If I was buying a house with a 15-20 year HVAC system, here's my approach:
First, I'd look at the service records. A well-documented system with annual maintenance gets the benefit of the doubt. No records? I'm factoring replacement into my budget.
Second, I'd get quotes during the inspection period. Not to necessarily demand replacement, but to understand my exposure. If the AC is 18 years old with no records, I want to know whether replacement is $5,000 or $10,000 before I finalize my offer.
Third, I'd consider a home warranty. For $500-700/year, you get some protection against the major failure that could happen in year one. It's not perfect coverage, but it smooths out the risk.
Fourth, I'd budget for eventual replacement even if nothing is wrong today. An 18-year-old system isn't going to run forever. Knowing that a $10,000 expense is coming in the next few years helps with financial planning.
The worst position is surprise. The furnace dies, you're scrambling for contractors, and you're paying whatever it takes to not freeze. A little advance planning goes a long way.