The replace furnace or air conditioner decision comes down to four checks, in this order. First, safety: a cracked heat exchanger or a venting problem on a gas furnace is a stop, not a repair quote. Second, age and repair history: ENERGY STAR suggests considering replacement when a heat pump or air conditioner is more than 10 years old, or a furnace or boiler more than 15. Third, refrigerant: an older system on R-22 costs more to keep charged. Fourth, ducts and sizing, which can make a new system perform no better than the old one.
Safety first: the part that is never a homeowner job
Before any of the money questions, one boundary. Diagnosing, repairing and replacing heating and cooling equipment is licensed work. Gas piping, combustion venting and electrical connections belong to a licensed HVAC contractor or gas fitter working under your local permit rules. Refrigerant handling requires an HVAC technician holding EPA Section 608 certification. This article helps you judge a recommendation. It does not tell you how to do the work.
If you have a gas, oil or propane furnace, carbon monoxide comes first. The U.S. Consumer Product Safety Commission's page on home heating equipment, read on September 27, 2026, urges a yearly professional inspection of all fuel-burning heating systems, including furnaces, boilers, water heaters, chimneys, flues and vents. Make sure the home has working carbon monoxide alarms.
If a technician tells you the heat exchanger is cracked, or that the furnace is venting exhaust into the house, treat that as a safety finding. Ask for it in writing, ask what they saw, and do not run the furnace until it is resolved. Getting a second opinion is reasonable. Ignoring it is not.
The four checks behind the replace furnace or air conditioner decision
Most repair-or-replace pages online come from contractors who sell replacements. That does not make them wrong, but it helps to run the decision in an order that puts the cheaper questions first.
- Is it safe? A safety finding on a combustion appliance overrides everything else.
- How old is it, and how often does it fail? Age alone is not a reason. Age plus a pattern of repairs is.
- What refrigerant does it use? This changes the cost of every future cooling repair.
- Is the equipment really the problem? Leaky ducts, a leaky house and the wrong size can all look like a failing system.
Many homeowners skip step four because nobody on the service call raises it. It is the step that decides whether a new system will actually fix the comfort problem you called about. The sections below take each check in turn.
Age, repairs and the ENERGY STAR signs
ENERGY STAR's "When is it time to replace?" page, read on September 27, 2026, lists these signs that it may be time to call a contractor about replacement:
- Your heat pump or air conditioner is more than 10 years old.
- Your furnace or boiler is more than 15 years old.
- Your equipment needs frequent repairs and your energy bills are going up.
- Some rooms in your home are too hot or too cold.
- Your home has humidity problems.
- Your heating or cooling system is noisy.
- Your home has excessive dust.
Read that list carefully. Only the first three point at the equipment itself. Uneven rooms, humidity, noise and dust can also point at the ducts, the sizing or the house. That is why the fourth check matters.
Some contractors use a formula that multiplies the unit's age by the repair cost and compares it with a fixed dollar threshold. It is a rule of thumb from the sales side, not a published standard. It says nothing about your ducts, your refrigerant or your house, so treat it as one input at most.
Refrigerant: why an older air conditioner costs more to keep
If your air conditioner or heat pump is older, check the nameplate on the outdoor unit for the refrigerant type. Many older systems use HCFC-22, often called R-22.
EPA's page on purchasing and repairing home air conditioners and heat pumps, last updated August 5, 2026 and read on September 27, 2026, makes several points worth knowing before you decide:
- Domestic manufacturers may no longer produce new HCFC-22, and importers may no longer import it.
- There is no EPA requirement to get a new system or convert an existing HCFC-22 unit.
- Technicians who repair leaks will most often continue to charge HCFC-22 into the system, because alternative refrigerants "will not work well without making changes to system components."
- Propane and other unapproved refrigerants are a fire or explosion hazard in home air conditioning systems.
So an R-22 system can legally keep running. The question is cost. A system that needs refrigerant added every season has a leak, and the leak is the repair. Ask the technician to find and fix it rather than top it up, and ask for the cost of both paths in writing.
Ducts: the fix that is often cheaper than a new system
This is the check most repair-or-replace pages skip.
Your furnace or air conditioner is rated at the equipment. The air still has to travel through ducts to reach the rooms. If supply ducts run through an attic, crawl space or garage and leak at the joints, part of the heated or cooled air never reaches the living space. A new system pushed through the same leaky ducts has the same problem.
ENERGY STAR's Clean Heating and Cooling page, read on September 27, 2026, says "poorly sealed duct systems can result in up to 30% loss in efficiency" and that "improper installation can reduce system efficiency by up to 30 percent." Those are ENERGY STAR's upper bounds, not a prediction for your house. They show why a replacement quote that ignores the ducts is incomplete.
What to look for yourself, without opening anything:
- Rooms at the end of long duct runs that never reach temperature.
- Dust streaks at duct joints or around supply registers.
- Ducts in an unconditioned attic or crawl space with visible gaps or loose tape.
Ask any contractor quoting a replacement to evaluate the ducts and include duct sealing as a line item or explain in writing why it is not needed.
Sizing and the house: what the new system has to heat and cool
A new system should be sized to the house you have now, not the one the old system was installed for. If you have added insulation, sealed air leaks or replaced windows since then, your home may need less capacity than before.
ENERGY STAR's Clean Heating and Cooling page says a contractor should use Manual J, which it describes as "a calculation of the amount of heating and cooling your home requires." "Same size as the old one" is not a Manual J.
This is also where the house itself comes in. A leaky, under-insulated house needs more heating and cooling, which can push a contractor toward bigger equipment. If replacement is not urgent, envelope work first can change the size you need:
- A DIY home energy audit shows where your house loses heat.
- A blower door test puts a number on how leaky the house is.
- Our guide to where the air leaks actually are covers the sealing, and the climate-zone answer on attic insulation covers the attic.
When the system has failed in January, none of this can wait. When it has not, it is worth doing first.
Replacing one piece or the whole system
A central system often has two halves: an indoor furnace or air handler with a coil, and an outdoor air conditioner or heat pump. When one half fails, you will usually be offered a choice between replacing that half or both.
The efficiency rating on a quote belongs to a matched combination of outdoor unit and indoor coil or air handler, not to one box. Replacing only the outdoor unit can leave you with a pairing the rating was not certified for. Ask the contractor to confirm that the specific combination they are quoting is certified, and ask for the AHRI reference number that identifies it.
A furnace is a separate case. Its AFUE rating sits on the furnace itself. A newer furnace with a failed air conditioner can reasonably stay, as long as the new outdoor unit is matched to the indoor coil it will actually use.
Whether both halves make sense to replace together depends on their ages, their condition and the quote. There is no public source that settles it for every house, so compare both options priced on the same scope.
Questions to put to every contractor
Take these to each quote so you can compare them honestly:
- What exactly failed, and what did you see? Ask for the diagnosis in writing.
- Is there a safety finding? If so, what is it, and is the appliance safe to run?
- What is the repair cost, and what is the replacement cost, for the same problem?
- What refrigerant does the current system use, and is the refrigerant being added because of a leak?
- Did you evaluate the ducts? What did you find, and is sealing included?
- How was the new system sized? Ask to see the Manual J.
- Is the quoted combination certified as a matched system?
- Who pulls the permit?
ENERGY STAR's Clean Heating and Cooling page suggests choosing a contractor who is licensed and insured, holds an industry-recognized installation certification such as NATE or ACCA, and has several years of experience in your community. Licensing rules vary by state and locality, so check with your local building department.
FAQ
How old is too old for a furnace or air conditioner?
ENERGY STAR suggests considering replacement when a heat pump or air conditioner is more than 10 years old or a furnace or boiler is more than 15 years old. Age alone is not a verdict. Repair history, safety, refrigerant and the ducts all matter.
Is it illegal to keep using an R-22 air conditioner?
No. EPA says there is no requirement to get a new system or convert an existing HCFC-22 unit. New HCFC-22 is no longer produced or imported, which is why repairs on these systems can cost more.
Should the furnace and air conditioner be replaced at the same time?
It depends on the age and condition of each. The cooling rating belongs to the matched outdoor unit and indoor coil, so ask whether a partial replacement keeps a certified combination. Compare both options priced on the same scope.
Can leaky ducts make a working system seem broken?
Yes. ENERGY STAR notes that poorly sealed duct systems can lose up to 30 percent in efficiency, and that uneven rooms and excessive dust are among the signs worth checking. Ask a contractor to evaluate the ducts before you accept that the equipment is the problem.
What should I do if the technician finds a cracked heat exchanger?
Treat it as a safety finding. Ask for the details in writing, do not run the furnace until it is resolved, and make sure your home has working carbon monoxide alarms. A second opinion from another licensed HVAC contractor is reasonable.