Furnace Replacement Cost Calculator

Start with output: the industry sizing chart runs 30–35 BTU per sq ft in warm climates, 40–50 in moderate ones and 50–60 in cold ones (Bryant's sizing guide). A 2,000 sq ft moderate-climate home therefore targets ~90,000 BTU of heat output. Divide by efficiency to get the input rating on the nameplate: that home needs a 120,000-BTU input furnace at 80% AFUE but only a 100,000-BTU one at 96%. Insulation, window area and ceiling height move the real answer — a Manual J load calculation, which good installers run before quoting, is the authority.

The added installation work — dedicated two-pipe PVC venting plus a condensate drain — runs roughly $900–$2,000 (UniColorado's 2026 guide prices the PVC flue upgrade at $899–$1,965), on top of the condensing unit's higher equipment price. In this model the whole-job gap lands near $1,789. Cold-climate homes burning a lot of gas commonly save on the order of $225–$300 a year going from 80% to 95% at typical utility rates, so heavy-use furnaces can pay the premium back — but an 80% furnace vented from an attic or crawlspace may never recoup it, because creating a combustion-air pathway through finished space is most of that added cost (PV Heating, Cooling & Plumbing's "80% vs. 95% Furnace Showdown" makes the same point). Parts of California now effectively require condensing units under 2026 NOx rules.

It's about how the burner fires. A single-stage furnace is full on or off — the classic blast of hot air then a cool drift. Two-stage (~15% equipment premium) runs a low flame most of the time, which evens out temperatures and noise. Modulating (~30% premium) varies the flame continuously with a variable-speed blower for the tightest temperature hold. The premium multiplies equipment cost, not labor, and pays back mostly in comfort rather than fuel savings — in short heating seasons the cheaper stage unit is often the rational buy.

If you have central AC, the evaporator coil sits on top of the furnace and shares its blower — when the furnace is replaced, the old coil above it is frequently mismatched, corroded or R-410A-legacy. Coil replacement runs $500–$2,500 all-in with a national average around $1,350 (Angi 2026 data), and doing it during the furnace job saves a second mobilization fee. Many manufacturers also tie warranty validity to matched pairs, so an unmatched old coil can leave you with a derated system and a void.

Angi's 2026 data puts a full oil-to-gas conversion at $3,800–$13,000, around $8,500 for many homes — the gas-line run length is the biggest variable. The project bundles the new furnace with a line from the meter, a pressure test, and draining, purging and disposing of the old oil tank. Local gas utilities frequently rebate part of a conversion, so check your utility's program before signing; the conversion itself typically takes 1–2 days of work once the utility has set the meter.

Yes, essentially everywhere — it's a combustion appliance tied to gas piping and venting. Municipal mechanical/gas permits commonly run $150–$600 depending on jurisdiction (valuation-based in cities like Los Angeles, flat fees elsewhere). The inspector pressure-tests the gas line, verifies vent sizing and material for the AFUE you chose, and checks carbon-monoxide safety at startup — the three failure points that put CO into living space. Your installer typically pulls the permit and books the inspection (often the same or next day); skipping it can void insurance claims, block a home sale and forfeit the manufacturer warranty registration.

A like-for-like change-out on an existing cabinet footprint and reusable venting is usually one 4–8 hour day: the crew sets the cabinet, transitions the plenum and return, hooks up the gas train and flue, then commissions the burn and airflow. Count on 6–10 hours when a 95% unit needs PVC venting routed to an exterior wall and a condensate drain run — the venting route is what adds the time — or when the shared AC coil is swapped in the same visit. An oil-to-gas conversion spans 1–2 days of trade work, plus however long your gas utility takes to schedule the meter set — often 1–2 weeks. Book early fall if you can: the first cold snap queues every no-heat emergency ahead of planned change-outs.

A condensing furnace extracts so much heat from combustion gas that the exhaust is cool and loaded with water vapor — mildly acidic condensate that cools further in a big metal B-vent and pools corrosive moisture. That's why 95%+ units must be direct-vented with dedicated PVC pipe (one for intake air, one for exhaust) and given a condensate drain, ideally through a neutralizer. An 80% furnace, by contrast, keeps hot enough flue gases to use the existing B-vent — which is exactly why the high-efficiency premium includes venting work.