Furnace Replacement Cost Calculator

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Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Heated home size: The finished area that the furnace heats, measured in square feet.

AFUE percent: Annual fuel utilization efficiency. It estimates the share of fuel energy that becomes usable heat over a heating season.

BTU per hour: A rate of heat output or input. Larger BTU per hour numbers mean more heating capacity.

Installed cost before credits: The estimated contractor project price before tax credits, utility rebates, or other incentives are subtracted.

Credits and rebates: Money you expect to get back or have applied through a tax credit, utility rebate, manufacturer rebate, or instant discount.

Local price level: A percent multiplier for local labor and market pricing. Use 100 percent for average pricing, below 100 for lower-cost areas, and above 100 for higher-cost areas.

Ductwork changes: Added cost for duct transitions, repairs, or replaced duct runs connected to the furnace project.

Manual J load calculation: A detailed residential heating and cooling load method used by HVAC contractors to size equipment more accurately than a square-foot shortcut.

Mistake: Entering total building area in Heated home size, including the garage or unfinished space.
Fix: Use only heated living area in sq ft so Rough heat needed by the home is not overstated.

Mistake: Picking Gas furnace but leaving Efficiency level on an electric or oil choice.
Fix: Match Furnace type and Efficiency level, such as Gas furnace with a gas AFUE option.

Mistake: Treating Credits and rebates as a discount on the contractor bid.
Fix: Keep Credits and rebates entered separate from Estimated installed cost before credits, then use Estimated cost after credits and rebates for planning cash out of pocket.

Mistake: Leaving Local price level at 100 percent when your area has unusually high labor or permit costs.
Fix: Raise Local price level, such as 110 or 120 percent, if recent local quotes run above average.

Mistake: Choosing "Ductwork changes" as "None" when the quote includes duct work. Fix: Select the matching scope for an illustrative comparison, then use itemized quotes to establish actual costs.

Mistake: Using Planning furnace size to ask about as the final equipment size.
Fix: Treat it as a conversation starter and ask the contractor to confirm sizing with proper load design.

• This is a budgeting estimate, not a contractor bid, code review, or Manual J load calculation.
• The heat need uses simple BTU per hour per sq ft shortcuts: 25 for mild, 35 for moderate, 45 for cold, and 55 for very cold winter areas.
• The cost tables are planning defaults. Brand tier, warranty, venting, electrical work, gas line changes, condensate drainage, access, and local code updates can move quotes outside the range.
• Credits and rebates are not checked for eligibility. The calculator subtracts the amount you enter and floors the after-credit result at $0.
• Major Ductwork changes can vary widely because full duct replacement depends on layout, material, airflow design, and access.
• The suggested furnace size is rounded up to the next 5,000 BTU per hour for planning. It is not a promise that a specific model size is correct or available.
• Oil, gas, and electric furnace costs are estimated from broad replacement categories. A heat pump, boiler, dual-fuel system, or full HVAC redesign is outside this calculator.

How the estimate is built

The calculator first estimates rough heating demand from Heated home size and Winter weather level.

estimated_heat_need = home_size_sqft * winter_btu_per_sqft

The shortcut values are 25 BTU per hour per sq ft for Mild winter, 35 for Moderate winter, 45 for Cold winter, and 55 for Very cold winter. This is only a planning shortcut.

Next, the selected Efficiency level is converted from AFUE percent to a decimal.

afue_decimal = afue_percent / 100

The rough furnace input size is the rough heat need divided by AFUE, then rounded up to the next 5,000 BTU per hour.

raw_input_btu = estimated_heat_need / afue_decimal

suggested_furnace_input_size = ceil(raw_input_btu / 5000) * 5000

Cost range steps

Each Efficiency level starts with a base installed price range for a 60,000 BTU per hour replacement. The base ranges are $4,500 to $6,500 for gas 80 AFUE, $6,000 to $8,500 for gas 95 AFUE, $7,500 to $10,500 for gas 97 AFUE, $3,000 to $5,500 for electric 100, $6,000 to $9,000 for oil 85 AFUE, and $7,500 to $11,000 for oil 90 AFUE. Installed furnace costs commonly vary by BTU size and efficiency tier [2].

The calculator adjusts that base range for furnace size. Smaller systems can lower the range, but the negative adjustment is capped at 25 percent of the base price so small homes do not produce unrealistically low project costs.

size_adj_low = max(base_low * -0.25, ((suggested_furnace_input_size - 60000) / 10000) * 180)

size_adj_high = max(base_high * -0.25, ((suggested_furnace_input_size - 60000) / 10000) * 320)

Ductwork changes then add $0 to $0 for None, $400 to $1,200 for Minor changes, or $3,000 to $8,000 for Major changes.

"Install difficulty" and "Local price level" adjust the base, size, and ductwork allowances. The entered "Old furnace removal" and "Permit and inspection cost" are added afterwards, unchanged, so a quoted fixed fee is not multiplied.

local_factor = local_price_factor_percent / 100

low_before = (base_low + size_adj_low + duct_low) * difficulty_factor * local_factor + old_unit_removal_cost + permit_and_inspection_cost

high_before = (base_high + size_adj_high + duct_high) * difficulty_factor * local_factor + old_unit_removal_cost + permit_and_inspection_cost

mid_before = (low_before + high_before) / 2

Credits and rebates are subtracted only after the before-credit installed cost is calculated. Gas and oil furnace incentives can depend on efficiency and program rules [1], so the calculator does not auto-apply a credit.

after_credits = max(0, mid_before - credits_and_rebates)

Worked example

For a 2,000 sq ft home in a Moderate winter area with a Gas high efficiency 95 AFUE furnace, a Typical swap, Minor Ductwork changes, $350 Old furnace removal, $200 Permit and inspection cost, 100 percent Local price level, and $0 Credits and rebates:

rough heat needed is 2,000 * 35 = 70,000 BTU per hour. The raw input size is 70,000 / 0.95 = 73,684 BTU per hour, rounded up to 75,000 BTU per hour. The installed range before credits is about $7,220 to $10,730, the middle estimate is $8,975, and the after-credit estimate stays $8,975.

Rounding and display

Money outputs are rounded to the nearest dollar and shown with commas. BTU per hour outputs are rounded to whole BTU values, with Planning furnace size to ask about rounded up to the next 5,000 BTU per hour.