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Heating & Cooling · ReplaceFurnace and AC Replacement
Furnace and AC replacement in one visit typically runs $7,500–$11,500 installed and saves $1,000–$2,500 over two separate jobs, because the labour, the sheet metal and the electrical overlap. Replace both when each is past about 12–15 years, or when the furnace is due and the air conditioner is an R-22 or older R-410A unit. If one of the two is under 10 years old and healthy, replace only the other.
The two machines are one system. The air conditioner's evaporator coil sits in the plenum on top of the furnace, the furnace blower is the only fan that moves cooling air through the house, and the efficiency printed on the AC label is only real when the furnace, coil and outdoor condenser are a combination listed in the AHRI directory. Put a new condenser on a mismatched coil and the rating on the box is not what you bought. An AHRI reference number for the exact three model numbers belongs on the quote.
Refrigerant is what forces the pairing for many houses. R-22 has been phased out and what remains is reclaimed stock, and new residential equipment now ships with R-454B or R-32 instead of R-410A. A new outdoor unit cannot be connected to an old coil built for a different refrigerant, so replacing the condenser means replacing the coil, and the coil is sitting on the furnace. If that furnace is a 1990s mid-efficiency unit, opening the plenum twice makes no sense.
Replacing only one is the right call more often than a sales quote admits. A furnace that fails at 16 years beside an 8-year-old R-410A air conditioner gets replaced alone, with the existing coil kept and re-fitted to the new cabinet and the blower set up for its airflow. An air conditioner that dies beside a 6-year-old furnace gets a new condenser and coil only. Should I replace my furnace and AC together works through the in-between cases, and what a furnace and AC combo costs breaks the price down.
Gas-served houses in Burlington, Oakville, Milton and Hamilton get a condensing furnace, 95% AFUE or better by federal rule, with a split air conditioner at or above the 13.4 SEER2 minimum. Rural Caledon, Kilbride and Carlisle lots beyond the gas mains run the same job on propane, or price a heat pump in place of the air conditioner. A real paired install is written up at furnace and AC replaced together. For the furnace side alone, see furnace installation, or request a written quote for both.
Replace both together when
- Both units are past about 12–15 years, whichever one failed first
- The air conditioner uses R-22, or it is an older R-410A unit with a leaking coil
- The furnace is an 80% mid-efficiency model with a metal flue and the AC needs a major repair
- The repair quote on either unit is more than half the cost of replacing it and the unit is over 12 years old
- You want a two-stage or variable-speed system, which needs a matched furnace, coil and condenser to work as designed
How it works
A heat-loss and heat-gain calculation sizes both units, static pressure tells us what the ducts can pass, and the quote names a furnace, coil and condenser that are an AHRI-listed match. We check the electrical disconnect, the line set route and the chimney on that visit.
Refrigerant is recovered from the old system by a technician holding an ODP card. The old furnace and coil come out, the new furnace and cased coil go in, and the plenum transition is rebuilt in sheet metal to fit them. The line set is replaced where it can be reached, or flushed and pressure-tested where it is buried in a finished wall, and the new condenser is set and brazed in.
The furnace is fired and checked for gas pressure, temperature rise and combustion. The refrigerant circuit is pressure-tested with nitrogen, pulled into a deep vacuum and charged by weight and measurement. In cold weather the charge is weighed in, and the running check of the cooling side waits for a day warm enough to load the condenser.
Common questions
How long does it take to replace a furnace and AC together?
Usually one working day for a straightforward swap, with the house without heat or cooling for those hours. A second day is needed when the line set has to be rerouted, when the plenum and return need more sheet-metal work than a transition, or when the water heater needs a chimney liner once the furnace stops using the flue.
Can my old line set be reused?
Often, when it is the diameter the new condenser's manual calls for, has no kinks or oil stains, and holds a nitrogen pressure test. It is flushed first to clear the old oil. A line set that served an R-22 system, is the wrong size, or has a buried joint gets replaced, even when that means a new route along the outside wall.
Can the AC be replaced in winter along with the furnace?
Yes. The furnace, coil, line set and condenser all go in, the refrigerant circuit is pressure-tested and evacuated, and the factory charge is adjusted by weight for the line length. What cannot be done at −5°C is a running check of the cooling charge, so that final measurement is taken once the weather warms up.
Should I price a heat pump instead of a new AC?
If you are replacing both anyway, yes. A heat pump is an air conditioner that also heats, and paired with a gas furnace as a hybrid it carries the mild months on electricity. Rebate rules favour heat pumps over furnace and AC pairs and they change, so check the rebates hub and get both options quoted in writing.
Do the furnace and AC have to be the same brand?
They have to be a listed match, which in practice usually means the same manufacturer family for the coil and condenser and a furnace whose blower is approved for that pairing. The AHRI directory lists the combinations and their certified ratings. A mixed set can run, but it carries no certified efficiency and can complicate a warranty claim, so we quote matched systems.