A ducted system properly looked after should last 15 to 20 years. Most of the systems we replace across Sydney fail somewhere between 12 and 18 years, usually because something major has gone (compressor, indoor fan motor, or the ductwork itself) and the repair quote sits uncomfortably close to the cost of a new system.

Knowing when you’ve hit that point matters, because the wrong call goes one of two ways. Replace too early and you’ve thrown out a system with years left in it. Wait too long and you’re throwing good money after bad on repairs to a system that’s going to die anyway, often during the first 38°C weekend in January when nobody can get to you for a fortnight.

Here are the five signs that tell us a system is genuinely on the way out, not just due for a service.

1. The power bill has crept up without the usage changing

If you’re running the system roughly the same hours as last year and the bill is meaningfully higher, the system is losing efficiency. A 15 to 20% efficiency drop over time is normal for a system that hasn’t been serviced. A 30%+ drop usually means something more serious: a refrigerant leak that’s left the system undercharged, a compressor that’s wearing out, or ductwork that’s been quietly leaking conditioned air into the roof space for years.

A service can sometimes recover that efficiency. On older systems past the 12-year mark, often it can’t. The components are simply at the end of their useful life.

2. Some rooms cool fine, others never quite get there

Even temperatures across the whole house is the entire point of ducted. When that breaks down (the living room sitting at 22°C while the back bedroom is still at 28°C), something has changed in the way the system distributes air.

The causes are usually one of: ductwork that’s collapsed, disconnected or sagging in the roof space, zone motors that have failed and are stuck open or closed, an indoor fan motor that’s lost capacity and can’t push air to the furthest vents, or a system that’s now undersized because the home has been extended.

Ductwork repairs are sometimes worth doing on a younger system. On an older one, where the existing ducts are likely also tired, replacing the whole system with new ducting is often better value than patching the old one.

3. Frequent repairs or unusual noises

The 12-month rule we use: if you’ve had two service calls in the same year, or one repair quote that’s more than a third of the cost of a new system, replacement is almost always the better call.

Specific noises worth paying attention to:

A grinding or screeching from the outdoor unit usually means the compressor or condenser fan motor is failing. Compressor replacement on an older system runs $1,500 to $3,000+, often more than the system is worth.

A loud rattle from the indoor fan coil in the roof points to fan bearings going. Indoor motor replacement is $600 to $1,200.

A persistent whistling or rushing sound from vents usually means duct damage. Could be a $200 fix, could be a full duct replacement.

A clicking or clunking when the system starts is usually a contactor or capacitor on its way out. Cheap to replace ($80 to $200) but a sign the electrical components are aging across the system.

One repair, particularly on a younger system, isn’t a reason to replace. Three repairs in two years on a system over 12 years old is a clear signal to stop spending money on it.

4. The controller is from a different era

If you’re still running the original wall thermostat from a 2008 install, the system underneath is from that era too. Older non-inverter systems run at one speed: full. They turn on, blast cold air, hit the set temperature, turn off, and wait for the room to drift before kicking back on. That cycle is hard on the components and expensive to run.

Modern inverter-driven systems modulate output continuously, which is quieter, cheaper to run, and gentler on the system. Pair that with proper zoning (MyAir 5, AirTouch 5, ActronAir Que, Daikin Zone Controller) and you’ve got a fundamentally different machine to what was sold a decade ago.

The controller upgrade alone isn’t usually possible on older systems. The control board, indoor unit and outdoor unit are an integrated package, and modern controllers don’t speak the language of older systems.

5. The system is past 12 years old and showing any of the above

Age on its own isn’t a reason to replace. Plenty of 14-year-old Daikin and Mitsubishi Electric systems are running fine across Sydney because they were properly sized, professionally installed, and serviced annually.

Age combined with any of the above signs is a different story. The components are all aging together. Once the compressor goes, the fan motors aren’t far behind. Once the ductwork starts leaking, the insulation in the roof is usually shot too. Replacing one piece on a system this old often just shifts the next failure six months down the road.

We also see manufacturer parts availability dropping off around the 15-year mark on most major brands. Once OEM parts go out of production, you’re either waiting weeks for a part to come in from overseas, or fitting a generic replacement that’s not quite the right spec.

A word on the home being extended or renovated

This catches plenty of homeowners off guard. A ducted system is sized to the house it was designed for. If you’ve added a room, opened up the kitchen, raked a ceiling, or put in floor-to-ceiling glazing, the original system is now undersized for the home it’s serving.

Symptoms include the system running constantly without ever quite hitting the set temperature, the new spaces being noticeably warmer or cooler than the rest of the house, and the power bill climbing because the system never gets a break.

This isn’t a fault with the system. It’s a sizing problem. Sometimes you can add capacity (an extra zone, an additional split for the new space). Sometimes the right answer is a properly sized replacement.

Repair vs replace: how we actually decide

The rough rule we use on a quote visit:

System under 8 years old: repair almost always wins, unless something catastrophic has happened (compressor failure, major duct collapse).

8 to 12 years: depends on the repair cost. If the quote is under 25% of new system cost, fix it. Above that, the maths gets harder.

12 to 15 years: if multiple components are aging or the system has known issues elsewhere, replacement usually wins on total cost over the next 5 years.

15+ years: any major repair quote is worth comparing directly to a new system. The new system will be more efficient, quieter, come with a fresh warranty, and likely outlive the next repair cycle.

A new ducted system in a four-bedroom Sydney home runs $9,000 to $14,000 supplied and installed for a competent mid-range setup. Larger or more complex installs push higher. We’ll always quote the genuine repair option alongside the replacement so you can compare like with like.

What to do next

If your system is showing one of these signs, book a service first. Sometimes the answer is a properly cleaned coil, a refrigerant top-up after the leak is fixed, or a duct repair, and you’ve bought yourself another five years.

If multiple signs are stacking up, or the system is past 12 years old and getting tired, it’s worth getting a replacement quote in parallel. Knowing what both options cost makes the decision straightforward.

Either way, get it sorted before summer. The worst time to discover the system needs replacing is the week of the first heatwave, when every installer in Sydney is booked out for a month.

Frequently asked questions

How long should a ducted air conditioner last? With annual servicing, 15 to 20 years is realistic. Without, 10 to 14 years is more typical, often with a major repair somewhere in the middle.

Is it worth repairing a 15-year-old ducted system? Depends on the repair. Minor repairs (capacitors, drain line, sensors) are usually worth doing. Major repairs (compressor, indoor fan motor, ductwork) on a system this old rarely make financial sense.

How long does a ducted replacement take? Most full ducted replacements run 1 to 2 days. Two-storey or more complex installs can push to 3 days. The system goes back to fully operational on the same day the install finishes.

Are there rebates available? NSW periodically runs energy efficiency incentives through the Energy Savings Scheme, and some manufacturers offer cashback promotions through the year. Worth asking at quote stage what’s currently available.