Repair vs Replace Furnace: Break-Even Calculator 2026

The repair wins today — the replacement wins the decade

A furnace repair is cheap and a new furnace is not — but a new unit runs cheaper every year, and over a decade that saving adds up. The repair total is just the repair cost: $800.00. The replace total is the new price, minus the saving over the old unit’s remaining life, plus disposal: $6,500 − $220 × 6 + $150 = $5,330.00. On the defaults — repair $800.00, new furnace $6,500.00, remaining life 6 years, saving $220.00/year, disposal $150.00 — REPAIR wins by $4,530.00; cost per year repair $133.33 vs replace $888.33; break-even repair $5,330.00, break-even price $1,970.00, break-even life 26.59 yrs (exact 26.5909), break-even saving $975.00/yr, break-even disposal none (-$4,380.00); 10-year repair-then-replace $6,570.00 vs replace-now $4,450.00 — REPLACE wins by $2,120.00 over 10 years.

At the defaults — repair $800.00, new furnace $6,500.00, remaining life 6 years, saving $220.00/year, disposal $150.00 — the repair total is $800.00, the replace total is $5,330.00, REPAIR wins by $4,530.00; cost per year repair $133.33 vs replace $888.33; break-even repair $5,330.00, break-even price $1,970.00, break-even life 26.59 yrs (exact 26.5909), break-even saving $975.00/yr, break-even disposal none (-$4,380.00); 10-year repair-then-replace $6,570.00 vs replace-now $4,450.00 — REPLACE wins by $2,120.00 over 10 years. Check the identities: repair = R; replace = P − S × L + D; difference = replace − repair; break-even repair cost = replace total; break-even new price = R + S × L − D; break-even remaining life = (P + D − R) ÷ S; break-even annual saving = (P + D − R) ÷ L; break-even disposal = R − P + S × L; 10-year repair-then-replace = R + P + D − S × (10 − L); 10-year replace-now = P + D − S × 10. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

The worked example, line by line

Setup: repair $800.00, new furnace $6,500.00, remaining life 6 years, saving $220.00/year, disposal $150.00.

Line 1 — the repair total. The repair total is the repair cost: $800.00.

Line 2 — the replace total. $6,500 − $220 × 6 + $150 = $6,500 − $1,320 + $150 = $5,330.00. The six years of saving shave $1,320 off the new unit’s price.

Line 3 — the winner. $5,330.00 − $800.00 = $4,530.00, so REPAIR wins by $4,530.00. Cost per year: $800 ÷ 6 = $133.33 for the repair, $5,330 ÷ 6 = $888.33 for the replacement.

Line 4 — the break-evens. The break-even repair cost is the replace total, $5,330.00. The break-even new price is $800 + $220 × 6 − $150 = $1,970.00. The break-even remaining life is ($6,500 + $150 − $800) ÷ $220 = 26.59 yrs (exact 26.5909). The break-even annual saving is ($6,500 + $150 − $800) ÷ 6 = $975.00/yr. The break-even disposal is $800 − $6,500 + $220 × 6 = -$4,380.00 — none, because the disposal cost that would tie is negative.

Line 5 — the 10-year lens. Repair now, then replace in 6 years: $800 + $6,500 + $150 − $220 × 4 = $6,570.00. Replace now: $6,500 + $150 − $220 × 10 = $4,450.00. So REPLACE wins by $2,120.00 over 10 years — the verdict flips over 10 years.

Reverse: the break-even repair cost is $5,330.00 (exact $5,330.00); a $5,330.00 repair costs $5,330.00, exactly tying the replace total — verdict: TIE. The break-even new price is $1,970.00 (exact $1,970.00); a $1,970.00 furnace costs $800.00 to replace, tying the repair — verdict: TIE. The break-even remaining life is 26.59 yrs (exact 26.5909); at 26.59 yrs the replace total is $800.20 (REPAIR wins by $0.20), at 26.58 yrs it is $802.40 (REPAIR wins by $2.40), at 26.60 yrs it is $798.00 (REPLACE wins by $2.00) — 26.5909 is the exact tie. The break-even annual saving is $975.00/yr (exact $975.00); at $975.00/yr saving the replace total is $800.00, tying the repair — verdict: TIE. The break-even disposal is none — the disposal cost that would tie is -$4,380.00; repairing wins even with free disposal — verdict: NONE. The 10-year lens: repair-then-replace $6,570.00 vs replace-now $4,450.00 — REPLACE wins by $2,120.00 over 10 years.

Every branch, checked

Repair $2,000: Repair $2,000.00, replace $5,330.00 — REPAIR wins by $3,330.00. 10-year: $7,770.00 vs $4,450.00 — REPLACE wins by $3,320.00 over 10 years. A $2,000 repair is still far cheaper than replacing — REPAIR wins by $3,330.00.

Repair $5,500: Repair $5,500.00, replace $5,330.00 — REPLACE wins by $170.00. 10-year: $11,270.00 vs $4,450.00 — REPLACE wins by $6,820.00 over 10 years. At $5,500 the repair costs more than the $5,330.00 replacement — REPLACE wins by $170.00, a flip from the default verdict.

10 years left: Repair $800.00, replace $4,450.00 — REPAIR wins by $3,650.00. 10-year: $7,450.00 vs $4,450.00 — REPLACE wins by $3,000.00 over 10 years. Ten years of $220 savings are worth $2,200, so the replace total falls to $4,450.00 — but REPAIR wins by $3,650.00 today; the 10-year lens is still REPLACE by $3,000.00.

12 years left: Repair $800.00, replace $4,010.00 — REPAIR wins by $3,210.00. 10-year: $7,890.00 vs $4,450.00 — REPLACE wins by $3,440.00 over 10 years. Twelve years of saving drop the replace total to $4,010.00 — REPAIR wins by $3,210.00 today. And the 10-year repair-then-replace is $7,890.00 — the unclamped (10 − L) = −2 means the replacement you buy in 12 years is charged with negative saving, so the path costs more, not less.

Saving $500/year: Repair $800.00, replace $3,650.00 — REPAIR wins by $2,850.00. 10-year: $5,450.00 vs $1,650.00 — REPLACE wins by $3,800.00 over 10 years. A $500-a-year saving pays for the new unit fast — the replace total is $3,650.00 and REPAIR wins by $2,850.00; over 10 years the replace-now total is $1,650.00.

Saving $0/year: Repair $800.00, replace $6,650.00 — REPAIR wins by $5,850.00. 10-year: $7,450.00 vs $6,650.00 — REPLACE wins by $800.00 over 10 years. With no saving the new unit costs its full price plus disposal — $6,650.00 — so REPAIR wins by $5,850.00 and the break-even remaining life is — (no saving, so no life ever ties).

New furnace $4,000: Repair $800.00, replace $2,830.00 — REPAIR wins by $2,030.00. 10-year: $4,070.00 vs $1,950.00 — REPLACE wins by $2,120.00 over 10 years. A cheaper new unit narrows the gap to $2,830.00 — but REPAIR wins by $2,030.00, the closest call on the page.

New furnace $9,000: Repair $800.00, replace $7,830.00 — REPAIR wins by $7,030.00. 10-year: $9,070.00 vs $6,950.00 — REPLACE wins by $2,120.00 over 10 years. A $9,000 unit is eleven times the repair — REPAIR wins by $7,030.00.

Disposal $0: Repair $800.00, replace $5,180.00 — REPAIR wins by $4,380.00. 10-year: $6,420.00 vs $4,300.00 — REPLACE wins by $2,120.00 over 10 years. Free haul-away drops the replace total to $5,180.00 — REPAIR wins by $4,380.00.

Disposal $600: Repair $800.00, replace $5,780.00 — REPAIR wins by $4,980.00. 10-year: $7,020.00 vs $4,900.00 — REPLACE wins by $2,120.00 over 10 years. A $600 disposal fee pushes the replace total to $5,780.00 — REPAIR wins by $4,980.00.

What the defaults assume

The model assumes the repair restores the old furnace for its full remaining life, and that the new unit’s saving is the same every year — it does not model a repair that fails again, a new unit that breaks early, or energy prices changing. It assumes the disposal fee is paid when you replace, not when you repair — you keep the old unit either way. It assumes the saving is real money: $220 a year of lower energy and fewer service calls. With a $0 repair the total is $0.00 and REPAIR wins by $5,330.00, but the 10-year lens is still REPLACE by $1,320.00. With 1 year left and no saving the break-even life is — — at the model level there is no life that ties, because the saving is $0; at the calc level S = 0 is valid input and the break-even-life field renders —. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures ($5,330.00, $1,970.00, 26.5909, $975.00, -$4,380.00) are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The homeowner with an $800 repair quote: they learn REPAIR wins by $4,530.00 — and they check the $5,500 branch (REPLACE wins by $170.00) to see the repair price where replacing wins.
• The owner whose unit has 12 years left: they learn REPAIR wins by $3,210.00 — twelve years of saving still lose to the cheap repair today — and they check the 10-year branch (REPLACE wins by $3,000.00 over 10 years) to see the decade margin.
• The shopper eyeing a $4,000 furnace: they learn REPAIR wins by $2,030.00 — the closest call on the page — and they check the $9,000 branch (REPAIR wins by $7,030.00) to see how fast a dearer model loses.
• The planner thinking in decades: they learn the 10-year lens flips the verdict — REPLACE wins by $2,120.00 over 10 years — and they check the $500-a-year branch (REPLACE wins by $3,800.00 over 10 years) to see the decade margin widen.

Accuracy & limitations

The math is first-principles comparison: repair = R; replace = P − S × L + D; difference = replace − repair; cost per year = total ÷ L; break-even repair cost = replace total; break-even new price = R + S × L − D; break-even remaining life = (P + D − R) ÷ S; break-even annual saving = (P + D − R) ÷ L; break-even disposal = R − P + S × L; 10-year repair-then-replace = R + P + D − S × (10 − L); 10-year replace-now = P + D − S × 10. The 4-decimal exact is shown where the rounding matters: the break-even remaining life is 26.5909 (shown as 26.59 yrs); at 26.59 yrs the replace total is $800.20 (REPAIR wins by $0.20), at 26.58 yrs it is $802.40 (REPAIR wins by $2.40), at 26.60 yrs it is $798.00 (REPLACE wins by $2.00). What the model cannot do is predict a furnace’s real life: a repair can fail again, a new unit can break early, and the saving depends on how much you run it — the break-even life of 26.59 yrs is the number to compare against your honest estimate of the old unit’s remaining life. For the same question on the cooling side, see the repair vs replace air conditioner calculator and the repair vs replace water heater calculator; for the size of the unit itself, see the furnace size calculator. This is a calculator, not a repair manual.