Furnace and AC Unit Replacement Cost: What to Budget in 2026

By Andrea · August 2026

Replacing a furnace and central AC at the same time is a bigger project than swapping one system alone — but it's often the smarter move. You share labor, the equipment is factory-matched, and you avoid tearing out a freshly installed unit two years later when the other half fails. The AC unit replacement guide covers the full cost picture for standalone AC; this page focuses specifically on the combined furnace-plus-AC scope.

Why Replacing Both at Once Changes the Cost Math

A furnace and AC unit share the air handler, blower motor, and ductwork. When a contractor pulls one system, they're already at the equipment — adding the second unit to the same job typically costs less than two separate service calls. There's also a technical reason: pairing a new high-efficiency AC condenser with an old furnace's air handler can create a mismatched system, which voids manufacturer warranties and limits efficiency gains. Starting fresh with a matched set solves that upfront.

The tradeoff is obvious: total outlay is higher on one bill. Financing through the contractor or a utility rebate program can soften that — many utilities offer rebates for meeting SEER2 and AFUE thresholds, so check with your local energy provider before finalizing the equipment tier.

What Drives the Final Price

• System size (tonnage): A 4-ton AC paired with a matched furnace handles roughly 2,000–2,400 sq ft in most climates; a 5-ton setup is typically for 2,400–3,000 sq ft. Each tonnage step raises equipment and labor cost, and oversizing carries real risk — a unit too large for the home will short-cycle, wear components faster, and leave the space humid. Always insist on a Manual J load calculation before finalizing size. For full cost ranges by tonnage without the furnace scope, see Central Air Conditioner Installation Cost.
• Efficiency tiers: The federal minimum for new central AC is 14.3 SEER2 (15.2 SEER2 in the Southeast and Southwest). For the furnace, 80% AFUE is entry-level; 95–98% AFUE modulating furnaces cost more but qualify for federal tax credits. Full efficiency-tier cost breakdowns for AC alone are at Central Air Conditioner Installation Cost.
• Ductwork condition: Intact, properly sized ducts keep the project scope tight. Leaky or undersized ducts can add more to the bill than the equipment itself — get a duct inspection included in any quote. Ductwork cost factors are covered in more detail under Central Air Conditioner Installation Cost.
• Refrigerant type: New equipment ships with R-32 or R-454B rather than R-410A, which is being phased out. If your existing line set is compatible it stays; if not, replacement is an additional line item. For how refrigerant type affects compressor replacement jobs specifically, see Ac Unit Compressor Replacement Cost.
• Labor and permits: Most jurisdictions require permits for both HVAC systems, and refrigerant handling requires EPA Section 608 certification. Labor rates vary by region — the Northeast and West Coast run higher than the South and Midwest. For a deeper look at how labor and permit costs factor into AC installation, see Central Air Conditioner Installation Cost.

What a Complete Quote Should Include

• AC condenser model, tonnage, and SEER2 rating
• Furnace model, BTU output, and AFUE rating
• Evaporator coil — whether it's being replaced or reused (reusing an old coil with new equipment can void the warranty; see AC unit coil replacement cost for what that adds)
• Refrigerant recovery, new charge, and leak test
• Permit procurement and inspection scheduling for both systems — see Central Air Conditioner Installation Cost for detail on what the permitting process typically involves.
• Removal and disposal of the old equipment
• Separate manufacturer warranty terms for the AC and furnace, plus the contractor's labor warranty — warranty coverage details for AC equipment are discussed at Central Air Conditioner Installation Cost.

Before You Sign a Contract

Get three quotes — on a project this size, the spread between contractors is often wide enough to change the decision. Confirm each contractor holds EPA Section 608 certification and a valid state HVAC license, and ask whether the quote assumes existing ductwork is in usable condition. For what to watch for when vetting contractors on AC-specific jobs, see Ac Unit Compressor Replacement Cost.