The problem
A furnace and an air conditioner installed in the same year tend to fail within a couple of winters of each other, which leaves the homeowner replacing one now and the other soon. Doing them separately means paying twice for the same plenum access, the same sheet-metal transitions and the same commissioning. It also leaves a new condenser running against an old evaporator coil that was never matched to it, so the SEER2 rating on the quote is not the one the house gets. If the old coil is an R-22 coil, it cannot run on the new refrigerant at all.
What we did
Replacing the pair together means the evaporator coil, the condenser and the furnace blower are selected as one AHRI-matched system, so the efficiency rating on paper is the one the house gets. The line set is inspected, flushed or replaced rather than assumed, the system is pulled into a deep vacuum before charging, and the refrigerant charge is weighed in and verified by subcooling under load. Doing both in a single visit means the supply plenum is cut once for the new coil instead of being opened again a year later.
- High-efficiency gas furnace
- Matched outdoor condensing unit
- New evaporator coil
- Line set and refrigerant charge
The result
A heating and cooling system that shares one set of transitions, one commissioning session and one warranty cycle. The combined job typically runs $7,500–$11,500 and saves roughly a thousand dollars against doing the two separately, which is why it comes up whenever a furnace is being quoted and the air conditioner is the same age.
Is this your situation?
This kind of work is worth a conversation if any of these sound familiar:
- Your furnace and air conditioner went in at the same time and are both around the same age.
- One of the two has failed and the other is on borrowed time.
- You would rather have one disruption, one set of sheet metal work and one warranty cycle.
- You want a matched coil and condenser so the published efficiency rating is the one you get.
Questions about this kind of job
What does a matched system mean and why does it change the efficiency?
The outdoor condenser, the indoor evaporator coil and the furnace blower are certified together by AHRI as a specific combination with a tested SEER2 rating. Pair a new condenser with a leftover coil and that certification no longer applies: the coil may be undersized, the metering device may be wrong for the refrigerant, and the efficiency, capacity and warranty are all reduced.
Can the old refrigerant line set be reused?
Often yes, provided it is the right diameter for the new equipment, has no kinks or corrosion, and can be flushed of the old oil. A line set from an R-22 system needs a flush before R-410A equipment goes on it, and manufacturers publish maximum lengths and rise. Where the line set is buried in a wall and cannot be verified, running a new one is the safer choice.
Is there any point replacing the furnace if only the AC has failed?
If the furnace is under 10 years old and running well, no. If both went in together and the furnace is 12 years or older, replacing it while the coil and plenum are already open avoids a second cut into the same sheet metal and a second commissioning visit. The decision rule is the age and condition of the furnace, not the fact that the AC failed.
How long does a combined furnace and AC replacement take?
Usually one working day for a straightforward changeout: the old equipment comes out in the morning, the furnace and coil are set and the transitions built, then the condenser, line set and electrical are finished and the system is evacuated, charged and commissioned. Chimney liner work, a new electrical circuit or duct modifications can push it into a second day.