How Long Does a Furnace Last? (Lessons From Years of Service Calls)

The nameplate said 2003. Mississauga, a two-storey on a quiet crescent, and the homeowner — mid-fifties, spreadsheet guy — had the blower motor quote in his hand — close to a thousand dollars, parts and labour. “The furnace is over twenty years old,” he said. “Be straight with me. Is this throwing good money after bad?”

Fair question. We get some version of it every week from October through March. Here’s the straight answer, then the full version.

The short answer: most gas furnaces last 15 to 20 years. A well-maintained one can hit 25. A neglected one can be done at 12. The number on the nameplate is only the starting point — what happened in the years since matters more.

What actually decides how long yours lasts

Annual maintenance. This is the big one, and it’s not close. A furnace that gets a professional tune-up every fall — burner cleaned, flame sensor checked, heat exchanger inspected, gas pressure verified — will outlive an identical unit that’s never been serviced by five years or more. We’ve pulled apart 20-year-old furnaces that look almost new inside because someone serviced them every year, and 10-year-old units that are rusted out because nobody ever did. Skipping a $200 tune-up to “save money” is how you buy a $7,000 furnace five years early.

Whether it was sized right. An oversized furnace short-cycles — fires up, blasts heat for eight minutes, shuts off, repeats. Every one of those cycles is wear on the ignitor, the blower motor, and the heat exchanger. A properly sized furnace runs longer, steadier cycles and lasts noticeably longer. If your furnace has been short-cycling since day one, its real age is older than the nameplate says.

How hard it works. A furnace in a drafty 1960s bungalow in Oakville with original windows runs a lot more hours per winter than the same furnace in a well-insulated 2015 build. More runtime, more wear. There’s nothing wrong with that — it’s the job — but heavy-use furnaces age faster. This is also why the thermostat wars matter less than people think: a steady 21°C is easier on the equipment than swinging between 18 and 24.

Installation quality. Undersized gas lines, sloppy venting, no combustion air, ductwork that chokes airflow — a bad install can take five years off a furnace before it ever really gets going. According to Natural Resources Canada, installation quality affects efficiency and equipment life as much as the equipment itself. If your furnace has had chronic problems since it was new, the install is the first thing we’d question.

The signs yours is on borrowed time

Your Enbridge bill keeps climbing. Same house, same thermostat setting, but January’s gas bill is 15 to 20 percent higher than it was three years ago. That’s efficiency bleeding away — usually a tired heat exchanger, worn burners, or a blower motor working harder than it should. A new 96% AFUE furnace uses roughly a third less gas than a 20-year-old 80% unit doing the same job.

Repairs are getting frequent and expensive. One repair in five years is normal. Two repairs in two winters on a 16-year-old furnace is a pattern. Our rule of thumb: if a single repair costs more than a third of a new furnace and the unit is past 15, the math almost never works. A $1,200 repair on a $6,500 replacement for a 17-year-old furnace is a bet you’ll usually lose within two seasons.

Some rooms never get warm anymore. When the far bedroom that used to be fine is suddenly cold every winter, and it’s not a duct problem, the furnace is losing capacity. Heat exchangers scale up inside over the years, blowers weaken, and the system just can’t push the heat it used to.

The burner flame is yellow instead of blue. Peek through the sight glass when it’s running. A healthy gas flame is steady and blue. Yellow, flickering, or lazy flames mean incomplete combustion. Either way, call a technician.

It’s past 15 and you’re planning to stay. This isn’t a failure sign, it’s a planning sign. At 15-plus years, start budgeting. Furnaces rarely die in September. They die in January, at 11 p.m., when every company in the GTA is booked solid and you’re paying emergency rates. Replacing on your schedule costs less than replacing on the furnace’s schedule.

A cracked heat exchanger. This is the safety red line, and it’s non-negotiable. The heat exchanger keeps combustion gases — including carbon monoxide — separate from the air blowing into your home. When it cracks, that separation fails. Symptoms can include a CO alarm going off, soot around the furnace, or a flame that dances when the blower kicks on. If a technician finds a cracked heat exchanger, the furnace gets red-tagged and shut down on the spot. No debate, no “let’s see how it goes.” On a furnace past 12 to 15 years, a heat exchanger replacement ($1,800 to $2,500 or more, parts and labour) is almost never worth doing — put that money toward a new unit.

How to squeeze more years out of the one you’ve got

Change the filter. Every 60 to 90 days, every 30 if you have pets. A clogged filter is the number one cause of overheating and short-cycling, and it’s a $20 fix for a problem that kills $7,000 equipment.

Keep supply and return vents open and unblocked. Closing vents in unused rooms doesn’t save money — it raises static pressure and strains the blower and heat exchanger.

Get the annual tune-up, every fall, before heating season. We check the heat exchanger with a camera scope, test for CO, clean the flame sensor and burners, verify gas pressure, and test every safety switch. It takes about an hour. It catches the small things — a weakening ignitor, a drain starting to clog — before they become midnight emergencies.

Don’t ignore new noises. A blower that suddenly sounds different, rattling that wasn’t there last winter, a new hum or whine — furnaces talk before they quit. The ones that “died suddenly” almost always gave weeks of warning.

Repair or replace: how we actually decide

Back to the spreadsheet guy in Mississauga with the aging furnace and the blower motor quote. Here’s the math we walked through together.

His furnace was well past twenty — past the typical range, living on bonus time. The repair was about 15 percent of a new furnace, not a third, so cost alone didn’t kill it. But the heat exchanger had never been scoped, the unit was an 80% efficiency model from 2003, and his gas bills had been creeping up for three winters. A new 96% two-stage furnace would cut his heating costs by roughly 25 to 30 percent and come with a 10-year parts warranty plus extended labour coverage.

He replaced it. Total installed: around seven thousand dollars for a high-efficiency two-stage unit. His January gas bill dropped noticeably the following winter.

That’s the framework: age, repair cost relative to replacement, efficiency gap, and the heat exchanger’s condition. Any two of those pointing the wrong way on a 15-plus-year unit, and replacement is usually the smarter money. A single cheap repair on a 12-year-old furnace that’s otherwise healthy? Fix it and keep going.

For reference, a new furnace installed in the GTA in 2026 typically runs $4,500 to $8,500 depending on efficiency (single-stage versus two-stage or modulating), brand, and installation complexity. The Ontario Save on Energy program periodically offers rebates on high-efficiency equipment — worth checking before you buy, since a qualifying 96%+ AFUE unit can knock hundreds off the net cost.

FAQ

My furnace is 18 years old and running fine. Should I replace it preemptively?
Not necessarily, but get the heat exchanger inspected and start budgeting. If the inspection is clean and it’s been maintained, running it another few years is reasonable. Just don’t be surprised when it quits — and have a plan that isn’t “call three companies during a cold snap.”

Does the brand matter for lifespan?
Less than maintenance and installation. A well-installed, well-maintained Goodman will outlast a neglected premium brand every time. That said, we install what we’d put in our own homes: as a Goodman Private Label Plus Dealer and Rinnai Pro installer, we stand behind Goodman and Rinnai, and we also carry Daikin, Amana, Lennox, Clean Comfort, Rheem, and Bradford White for the same reason — they’re built to last when they’re installed right.

How much does an annual furnace tune-up cost?
In the GTA, a proper professional tune-up runs $150 to $250. It should include heat exchanger inspection, CO testing, burner and flame sensor cleaning, gas pressure check, and safety control testing — not just a filter change and a sticker. If a “tune-up” takes 15 minutes, it wasn’t one.

Can a furnace really last 25 years?
Yes, we’ve serviced them. The 25-year furnaces all have the same story: annual maintenance without gaps, correct sizing, decent installation, and owners who changed filters. It’s the exception, not the rule — plan for 15 to 20, and anything beyond that is a bonus.

Is it safe to keep running a very old furnace?
Age alone isn’t dangerous, but neglect is. The real risk is a cracked heat exchanger leaking carbon monoxide, which is why annual inspection with CO testing matters more as the unit ages. Keep a working CO alarm on every floor regardless — it’s the cheapest life-safety device in your house.

What’s the actual efficiency difference between my old furnace and a new one?
A furnace from the early 2000s is typically 80% AFUE — 20 cents of every heating dollar goes up the chimney. A new high-efficiency unit is 96 to 98% AFUE. On an average GTA winter gas bill, that gap is worth several hundred dollars a year, which is part of why replacement math often works even before the old unit fully dies.

If your furnace is getting up there in years and you’re not sure where it stands, we’d rather check it in October than meet it in January. Call First Choice Heating & Air Conditioning at 905-334-7885 — we’ll scope the heat exchanger, test for CO, and give you a straight answer on whether you’ve got years left or you’re on borrowed time. TSSA-certified, our own technicians on every call, never subcontracted, and we’re available 24/7 when the heat quits at the worst possible moment.

About First Choice Heating & Air Conditioning: First Choice Heating & Air Conditioning provides residential heating and cooling services in Oakville and surrounding GTA communities, including furnace, air conditioning, heat pump, ductwork, water heater, and indoor air quality services.