Quick Answer
Often, yes — if both are getting old. Your furnace and central AC share the same blower and ductwork, so replacing them together gives you a properly matched system, one installation instead of two, and warranties that start at the same time. If one of them is still fairly new, replacing just the older one usually makes more sense.
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When your furnace or air conditioner needs replacing, it’s worth asking about the other one too. Here’s when replacing both makes sense — and when it doesn’t.
How Your Furnace And AC Work Together
In most Ottawa homes, central air isn’t a separate system. The AC coil sits on top of the furnace, and the furnace’s blower pushes both warm and cool air through the same ductwork. That means the two need to be matched — a new AC paired with an old furnace blower may not deliver the airflow it was designed for.
Benefits Of Replacing Both At Once
- A properly matched system. The furnace blower and AC coil are sized to work together for the best comfort and efficiency.
- One installation. Much of the labour overlaps, so a combined project can cost less than two separate ones — and you only deal with the disruption once.
- Warranties on the same timeline. Both systems start fresh together, instead of one aging out while the other is new.
- No surprise second project. If both are old, replacing one now often means replacing the other in a year or two anyway.
When It Doesn’t Make Sense
- One system is still fairly new and running well
- The newer system is compatible with the replacement and has plenty of life left
- Your budget only allows for one project right now — replace the one that's failing
Ask About Compatibility
If you’re only replacing one system, ask your technician to confirm the new equipment is compatible with the one you’re keeping — especially the AC coil and the furnace blower.
What To Do, By Age
Furnaces typically last 15 to 20 years, and central air conditioners about 10 to 15. Use their ages as a guide:
| Your Systems | Usually The Best Move |
|---|---|
| Both 12–15+ years old | Replace both together |
| Old furnace, AC under ~8 years | Replace the furnace; keep the AC if it's compatible |
| Old AC, furnace under ~8 years | Replace the AC, with a coil matched to your furnace |
| Both under ~10 years | Keep both, and service them yearly |
What It Costs
In Ottawa, a new furnace typically costs about $3,500 to $8,000 installed, and a central AC system about $3,500 to $7,000 in a home with existing ductwork. Replacing both together can cost less than doing them separately, since much of the labour overlaps. See our furnace replacement cost guide and central AC cost guide for the details.
Energy rebate programs change often, and eligibility depends on your home and the equipment — ask what’s currently available when you get a quote.
The Bottom Line
If your furnace and AC are both 12 to 15+ years old, replacing them together usually makes sense: a matched system, one installation and warranties that start together. If one is still fairly new, replace the older one — and make sure the new equipment is compatible with the one you’re keeping.
Learn more about our furnace replacement and AC installation services.
