HVAC Cost Calculator: Get an Exact Furnace and AC Replacement Price Online

The online HVAC estimate asks up to five questions, and every answer narrows the price until you are looking at one number. It only shows choices that have a real price behind them, so you never land on "call for pricing."

Each price is the installed price, not an equipment price with labor added later. It covers:

The estimator sizes equipment from your above-ground square footage, using the same starting chart FortHouse uses on site. The free in-home visit then confirms the size against the house itself: insulation, windows, duct sizes and how the home actually heats and cools.

Air conditioner size by square footage: up to 1,400 sq ft gets a 2-ton AC; 1,401–2,100 sq ft a 3-ton; 2,101–2,500 sq ft a 3.5-ton; 2,501–2,900 sq ft a 4-ton; over 2,900 sq ft a 5-ton.

High-efficiency (96%+) furnace size: under 1,000 sq ft gets 40,000 BTU; 1,000–1,999 sq ft 60,000 BTU; 2,000–2,699 sq ft 80,000 BTU; 2,700–3,400 sq ft 100,000 BTU; 3,401+ sq ft 120,000 BTU.

Standard (80%) furnace size: under 1,200 sq ft gets 60,000 BTU; 1,200–1,999 sq ft 80,000 BTU; 2,000–2,699 sq ft 100,000 BTU; 2,700–3,400 sq ft 120,000 BTU. An 80% furnace burns more gas to deliver the same heat, which is why it steps up in size sooner.

When the furnace and AC are replaced together, the estimator also matches the furnace's blower and cabinet width to the AC and its coil, so the two systems move the right amount of air together.

These are real results from the instant estimate, installed, for a few common homes. Your exact price depends on your square footage and the equipment you pick.

With standard Goodman equipment, a new furnace and AC installed together run $10,000–$15,850 in the estimator, depending on home size and efficiency. That sits inside the $10,000–$17,000 range FortHouse quotes for a complete system on its HVAC replacement page; the top of that range is the modulating and communicating equipment the online tool leaves out (more on that below).

Replacing both at once also costs less than replacing them separately. In a 1,401–1,999 sq ft home, a 96%+ single-stage furnace with new venting is $5,350 on its own and a 3-ton 13.4 SEER2 AC is $6,350 on its own: $11,700 if you do them on two visits. Together, the same equipment is $10,450, about $1,250 less, because one crew, one permit and one startup cover both. Why replacing both together costs less goes deeper on when that is worth doing.

An 80% furnace turns 80 cents of every gas dollar into heat and vents into your existing chimney or metal flue. A 96%+ furnace turns 96 cents or more into heat and vents through PVC pipe out the side of the house. ENERGY STAR's furnace criteria set the bar for certified gas furnaces at 95% AFUE or higher for northern climates like Illinois.

The estimator asks whether your current furnace is high-efficiency because it changes the work. If you already have white PVC pipes, the new 96%+ furnace reuses that path and the price is lower. If you are moving from an 80% furnace, the price includes new PVC venting. Two-stage furnaces run on a low setting most of the time, which means steadier temperatures and a quieter system.

SEER2 is the cooling efficiency rating. A new central AC in Illinois has to meet the 13.4 SEER2 federal minimum for the North region, so 13.4 SEER2 is the baseline. A 14.3 SEER2 unit is about 7% more efficient and a 15.2 SEER2 unit about 13% more efficient than that minimum. SEER2 ratings explained covers how much of that shows up on a ComEd bill.

Modulating furnaces, variable-speed air conditioners and communicating systems are not in the calculator. They need a matched coil and thermostat that change from house to house, so FortHouse quotes them one at a time. Send a note through the contact form or email comfort@forthousehvac.com for a written price.

Duct work is also separate. Most homes can reuse their ducts, and when a home needs duct changes they are quoted on top of the installed price. Heat pumps, ductless mini-splits, repairs and tune-ups have their own pages and prices; the price sheet for Plainfield and Naperville lists them all.

Once you have a price, book a free in-home visit straight from the estimate page. A FortHouse technician measures the home and checks the venting, electrical and ducts. If anything changes the number, you get the new number in writing before any work starts. Most replacements take a single day, and FortHouse answers the phone 24 hours a day, 7 days a week at (630) 318-6246.

A good HVAC cost calculator should give you the price you will actually pay, not a national average. FortHouse's instant online HVAC estimate does that for Plainfield, Naperville and the western suburbs: furnace and AC together from $10,000, a furnace only from $5,000, an AC only from $5,800, installed, with the exact Goodman models listed. It's free and takes about a minute, and you don't have to give a phone number.