The furnace blower runs the AC too
Your furnace heats the air, and its blower also moves the air for cooling. The AC's indoor half, the evaporator coil, sits on top of the furnace in that airflow. Two copper pipes, the line set, run from that coil out to the condenser beside the house: a fat insulated suction line and a thin liquid line.
What gets touched either way
Replace either side and the installer works on the same connections: the sheet-metal transition between furnace and coil, the condensate drain, the thermostat wiring, and often the refrigerant lines. Replace the other side a few years later and much of that work happens again.
When doing both makes sense
- Both units are past about 15 years, or the AC uses R-22 refrigerant.
- The furnace needs a major repair and the AC is close behind.
- You want a heat pump. It replaces the AC outside and keeps the furnace as backup, so the pair gets designed together anyway.
When it doesn't
If one side is young and healthy, keep it. The new equipment gets matched to what stays, and the quote should say what the later replacement will reopen: usually the coil, the line set and the drain.
See what each path costs or plan the timing. For your own price, send four photos.
Common questions
Can I replace just the AC and keep my furnace?
Often, yes. The new coil has to fit the furnace cabinet and work with its blower, so the installer checks the furnace model and its condition first. If the furnace is near the end of its life, the coil and transition may get reworked again when it goes.
Is it cheaper to do both at once?
In our recent Denver estimates, a furnace and an AC priced as separate jobs add up to about what one combined job costs. Doing both at once saves the second visit and a coil refit later, because the coil, transition, drain and startup are done once.