Furnace Replacement: What It Actually Costs

Sizing and Efficiency Are What Set the Price

Furnace cost is driven by two things: how much heating capacity your home needs (measured in BTUs) and the AFUE rating, which is the percentage of fuel the unit actually converts into usable heat rather than losing up the flue. A standard-efficiency furnace runs 80% to 85% AFUE. A high-efficiency condensing furnace runs 90% to 98.5%, capturing extra heat from the exhaust that older units simply vent outside. That difference costs more upfront and pays it back gradually through lower gas bills.

How to Tell It's Time to Replace, Not Repair

A furnace over 15 years old that needs a repair costing more than a third of a new unit's price is generally not worth fixing again. Age alone isn't the only signal though. Rising energy bills without a change in usage, uneven heating between rooms, a burner flame that's yellow instead of blue, and short-cycling (turning on and off repeatedly without completing a full heating cycle) all point toward a system on its way out rather than one that needs a minor part swapped.

• A cracked heat exchanger is an automatic replace, not repair, situation. It's a carbon monoxide risk, and most technicians won't attempt to patch one.
• Fuel type matters for the swap, not just the unit. Converting from oil or propane to natural gas adds line-running costs on top of the furnace price itself, sometimes a meaningful chunk of the total project.

Ductwork Condition Affects the Real Cost More Than People Expect

A brand-new high-efficiency furnace connected to old, leaky, or undersized ductwork won't deliver the efficiency gains the AFUE rating promises, since a meaningful share of the heated air simply escapes before it reaches the rooms. Sealing and insulating existing ducts, or resizing sections that were never adequate for the home's layout, is a common add-on that homeowners don't always anticipate when budgeting only for the furnace unit itself. A technician doing a proper load calculation before installation should flag duct problems as part of that assessment, not leave them for a callback later.

Matching the Thermostat and Controls to the New System

Two-stage and modulating furnaces need a compatible thermostat capable of communicating with the unit's variable-speed controls, which a basic single-stage thermostat can't do. Upgrading to a compatible smart or communicating thermostat typically adds $200 to $500 to the project, but skipping it on a high-efficiency furnace means the unit runs in a simplified mode that doesn't take advantage of the efficiency features being paid for in the first place.