If both your furnace and air conditioner are old and one has already quit, replacing them together in Castle Rock usually makes sense. The two share a blower and the same ductwork, so pairing a new furnace with a new AC lets them run as one matched system instead of a mismatch that fights itself. When only one unit is failing and the other still has good years left, replacing both at once is not required, and you should not feel pushed into it.
Here in Castle Rock, above 6,000 feet in the East Plum Creek Valley, homes lean hard on the furnace through long, cold winters and use the AC in shorter bursts through warm, dry summers. That difference in workload is the whole reason this question comes up so often.
Because the furnace usually carries the heavier load year after year, it often reaches the end of its life on a different timeline than the AC that sits outside. When you replace a furnace, the indoor evaporator coil that your AC depends on sits right on top of it, and a new high-efficiency furnace paired with an old, lower-efficiency AC can leave you short of the comfort and savings you paid for. That is why a good replacement conversation always looks at both pieces, even when only one has failed.
Is it cheaper to replace furnace and AC together?
Replacing both at the same time can lower your total cost compared with doing two separate jobs a few years apart, mostly because you share the labor. One trip, one crew, one setup, and one round of connecting the coil, refrigerant lines, and electrical instead of paying for all of that twice.
The savings are real but not unlimited, so treat the discount as a bump, not a windfall. Equipment is still the biggest line item, and two pieces of equipment cost more up front than one. The trade-off is simple: bundling saves you on labor and disruption now, while splitting the jobs spreads the spending out but usually costs more in total. If your AC is genuinely mid-life and healthy, stretching it out can be the better call.
Does the R-454B refrigerant change affect replacing my AC and furnace?
It affects the AC, not the furnace, since furnaces do not use refrigerant. As of January 1, 2025, manufacturers stopped building new residential AC and heat pump equipment that uses R-410A, and new systems now use lower-GWP refrigerants like R-454B. If you buy a new air conditioner today, it is almost certainly an R-454B system.
Your existing R-410A air conditioner is not illegal and does not have to be torn out. Existing R-410A systems can keep running and can still be serviced and repaired, and the EPA has not set a date that ends servicing of legacy equipment. R-410A and R-454B are not interchangeable, though, so you cannot just top off an old system with the new refrigerant. Where this ties back to your furnace question: if you are already replacing the furnace and your AC is aging, doing both now means the new coil is matched to a new R-454B condenser from the start, rather than mating a fresh coil to an old refrigerant setup you will replace soon anyway.
Do furnaces last longer than air conditioners?
Yes, a furnace usually outlasts a central air conditioner, though often by only a few years. A gas furnace commonly lasts 15 to 20 years or more with good care, while a central AC more often lands around 12 to 17 years. That gap is why many Castle Rock homes do not hit both replacements at the same moment.
Part of the reason is runtime. In our climate the furnace works through a long heating season while the AC runs in shorter summer stretches, yet the outdoor condenser still takes the beating of sun, wind-driven dust, and freeze-thaw swings up here on the Front Range. If your furnace is already past 15 years old, check the age of your AC too. When it is close behind, planning the second replacement early beats getting surprised by it.
Will a furnace work if the AC is broken?
Yes. A broken air conditioner does not stop your furnace from heating. The two are separate systems that only share the blower, the ductwork, the thermostat, and the AC coil that sits on top of the furnace. Your furnace burns gas and pushes warm air on its own, so if the AC fails in August, you will still have full heat when the cold returns.
The blower is the shared part to watch. A dead AC does not touch your heat, but a dead blower motor takes out both. So if your AC quits, there is no emergency reason to replace the furnace along with it, and you can heat your home all winter while you plan the cooling fix on your own schedule. The reverse matters more in Castle Rock: losing the furnace mid-winter, with overnight lows that regularly drop into the teens and single digits, is the real emergency. If your heating system is the piece that is struggling, that is the one to move on first.
When your furnace or AC is near the end and you are trying to decide whether to bundle the work, the smartest first step is knowing the true condition and age of both units in your specific home. Our NATE-certified, technician-owned team handles furnace replacement in Castle Rock, can diagnose both units, run the numbers on doing one now versus both together, and pull any permits the job needs so nothing falls on you. For a free estimate or diagnostic visit anywhere in Castle Rock, reach out to Alpha Air Heating & Cooling at (720) 284-9566.
