What a new furnace really costs, and what moves the price.

1. Efficiency, measured in AFUE. AFUE is simply the percentage of fuel that becomes heat in your home rather than escaping up the flue. An older furnace often runs about 80% — meaning a fifth of every fuel dollar is wasted. A 90–98% AFUE condensing furnace costs meaningfully more upfront and typically requires new PVC venting, because its exhaust is cool and acidic and cannot use the old metal chimney. In a cold climate with a long heating season the efficiency upgrade pays back; in a mild one it often does not. Ask for the payback period in years, not a vague promise of savings.

2. Staging and blower type. A single-stage furnace is either full-blast or off, which produces temperature swings and noise. A two-stage runs at a gentler output most of the time. A variable-speed (modulating) furnace continuously adjusts and is markedly quieter and more even, at the highest price. Comfort improvements here are real and noticeable, but they are comfort, not savings — judge them on that basis.

3. Correct sizing, which nobody should skip. The right size comes from a load calculation against your square footage, insulation, windows and layout — not from matching whatever was there before. Oversizing is rampant because it is the safe guess for an installer, but an oversized furnace short-cycles, wears out early and heats unevenly. If a contractor quotes without measuring anything, that quote is worth less than it looks.

4. The work around the furnace. This is where two quotes for the "same" furnace differ by thousands. New venting for a condensing unit, a condensate drain, resized or resealed ductwork, gas line adjustments, electrical work, permits and disposal of the old unit all cost real money. A suspiciously cheap quote usually has these stripped out, and you pay for them later in poor performance or a failed inspection.

How to compare quotes fairly. Get the model number, the AFUE, the staging, and an itemised list of the work — then compare like for like. Ask what the labour warranty is, separately from the manufacturer's parts warranty, because the install is what usually fails first. Ask which utility rebates apply; high-efficiency equipment frequently qualifies and a good contractor handles that paperwork. And ask whether financing is available if spreading the cost matters more to you than the headline price.