Full System Replacement Cost: Furnace + AC

When your furnace and your central air are both getting old, there is a real question worth asking before you spend a dime: should you replace them together? Doing both at once, often called a full system replacement, typically runs between $9,000 and $18,000 installed on the North Shore. That is a bigger check than replacing one unit, but when both are near the end of their lives, bundling usually costs less than two separate jobs and leaves you with a better-performing system. This guide explains why that is, when it makes sense, and how the numbers compare. As always, a written in-home estimate is the only way to get a true figure for your home, but the logic here helps you decide whether to bundle or not.

What a full system costs in 2026

A full system replacement covers a new furnace, a new central AC condenser, and the matching indoor coil, installed together. Treat every number below as a typical range that shifts with your equipment, home configuration, and the market.

These are installed prices covering both units, the coil, labor, the permit, and startup. If you want to dig into either half on its own, we have detailed breakdowns in furnace replacement cost and AC replacement cost.

Why bundling usually saves money

Replacing both units in one project is not just convenient; it genuinely lowers the total in several ways.

• One install visit. A furnace and an AC coil share the same cabinet space and much of the same labor. Doing them together means one setup, one crew mobilization, and one round of removal and haul-away instead of two.
• Matched equipment. A furnace and AC that are engineered and installed as a set work together cleanly. The blower in the furnace moves the air the AC coil cools, so matching them means the system runs at its rated efficiency rather than fighting a mismatch.
• Better efficiency, one time. If you are upgrading both to high-efficiency at once, you get the full benefit across heating and cooling seasons, and you only pay for the venting and setup work once.
• Stacked rebates. When both units qualify for utility rebates, you may be able to claim incentives on the furnace side in the same project, which softens the total. More on that below.

None of this means bundling is always right. It makes sense specifically when both units are near the end of their service life.

When it makes sense to do both

The clearest case for a full system replacement is when both units are aging out at the same time. If your furnace is fifteen-plus years old and your AC is close behind, replacing them separately a year or two apart means paying for two install visits and living with a mismatched system in between. Bundling avoids both.

A few other situations point the same way:

• Your AC runs on R-22 refrigerant and needs a costly repair, and your furnace is also old. Rather than recharge a dying AC and replace the furnace separately, doing both makes sense. We cover the R-22 issue in repair or replace your AC.
• You are upgrading to high-efficiency and want the furnace and AC matched to perform together.
• Your indoor coil needs replacing anyway. Since the coil sits on the furnace and the labor overlaps, adding the furnace to the job is often marginal cost rather than a whole second project.

If only one unit is truly at the end of its life and the other has good years left, replacing just the one you need is the honest, lower-cost choice. There is no reason to replace a healthy unit to force a bundle. And whichever route you take, correct sizing still matters for both units, which we cover in right-size your HVAC with a load calculation.

Separate vs together: how the numbers compare

The table below is illustrative, not a quote, and the real figures depend entirely on your equipment and home. The point is the pattern, not the exact dollars.

The bundled path usually comes out ahead when both units are due, mostly because you are paying the shared labor and mobilization once instead of twice. When one unit clearly has life left, that math flips, which is why the honest recommendation always starts with the actual condition of your equipment.

What a fair full-system quote should include

Because a full system is a larger purchase, the itemized quote matters even more. A complete quote should spell out both units and the coil clearly:

• The furnace make, model, BTU size, and AFUE rating
• The AC condenser make, model, tonnage, and SEER2 rating
• The matching indoor coil, listed as its own line item
• Venting and a condensate drain for a condensing furnace
• Line set handling and any electrical work for the AC
• A new thermostat, or confirmation your existing one is compatible
• The permit and required inspections
• Removal and haul-away of both old units
• Startup, testing, and a full walkthrough

When a bundled quote is a single lump sum with no breakdown, ask the installer to itemize it. You want to see that both units are properly sized and matched, not just a total dropped at the bottom of the page.

What to watch out for

Most installers on the North Shore do honest work, but a few warning signs apply to full-system jobs specifically:

• Pressure to replace a healthy unit. If one of your units genuinely has good years left, replacing it to force a bundle is not in your interest. A trustworthy installer will say so.
• No load calculation. Both units need to be sized to your home, not copied from the old equipment. Skipping that step leads to comfort and efficiency problems.
• No permit. A full system replacement requires permits and inspections in Cook and Lake County towns. Skipping them dodges the safeguard that protects you.
• A total that seems too low. As with any HVAC job, a number well below the others usually means something was left out, and you will meet it as a change order later.

Rebates in 2026

For 2026, utility rebates are the main incentive, since the federal 25C tax credit expired for equipment placed in service after December 31, 2025. On a full system, the furnace side is where most of the rebate action is: Nicor Gas offers roughly $225 for a qualifying 97% AFUE furnace and up to about $100 for a qualifying smart thermostat, with roughly 90 days to file. Some North Shore towns are served by North Shore Gas rather than Nicor, so check your gas bill and look up that program. Rebate amounts change, so verify the current numbers before you count on them. Our ComEd and Nicor HVAC rebates guide keeps a fuller breakdown.

Homeowners across Northbrook, Deerfield, and Lake Forest often replace both units together when the timing lines up, and the range in this guide holds up well across the North Shore. Your home is its own situation, though. For a real number on a matched furnace and AC, book a written full system replacement estimate or get our free estimate. You can also call (847) 752-4418 and a licensed installer will assess whether bundling is truly the right move for you.