The one-third rule, and why the age matters
A gas furnace in Arvada lasts 15 to 25 years. The difference between 15 and 25 is mostly maintenance, filter habits, and whether the furnace was sized right for the house and the altitude. Past 15, the parts that fail start to be the expensive ones (blower motors, inducers, boards, heat exchangers), and each repair buys less time because the next failure is already queued up.
So the rule: multiply the furnace age by the repair cost. If the answer is over $5,000, replacement usually wins. A $600 repair on a 10-year-old furnace is $6,000, borderline. A $600 repair on a 6-year-old is $3,600, repair it. A $1,200 blower motor on an 18-year-old furnace is $21,600, replace. The one-third rule and the age-times-cost rule land in the same place; use whichever is easier to hold in your head at the kitchen table.
Cost table by furnace age
Prices verified September 2026| Furnace age | Repair when | Replace when |
|---|---|---|
| Under 10 years | Almost always. Most parts are still under manufacturer warranty (check the sticker and registration). Labor $150 to $600. | Only for a cracked heat exchanger outside warranty, or a furnace that was badly oversized and has short cycled since day one. |
| 10 to 15 years | Repairs under $800. Ignitor, flame sensor, pressure switch, capacitor, limit, condensate. | Repairs over $1,200, or a second major part within two years. Blower motor plus board is the classic pair. |
| 15 to 20 years | Repairs under $500, and only if the heat exchanger inspects clean. | Any repair over $1,000. Any heat exchanger issue. An 80 percent furnace here is also the strongest rebate case for moving to 95 percent or a heat pump. |
| Over 20 years | Repairs under $400 that get you through this winter while you plan. | Almost everything else. Parts are becoming hard to find, efficiency is 60 to 78 percent, and the heat exchanger is at the end of its design life. |
| Repair ranges from the Arvada repair price list. Replacement $3,500 to $10,400 installed, from the replacement cost page. Q3 2026. | ||
The repairs that tip the decision
Heat exchanger: replace
$1,000 to $3,700 to replace the exchanger alone, and on a furnace old enough to crack one, the blower, inducer, and board are the same age. Almost nobody puts a new heat exchanger in a 16-year-old furnace once they see both numbers. The exception is a furnace under 10 with the exchanger under the manufacturer's 20-year parts warranty, where the part is covered and you pay labor.
Blower motor on a high-efficiency furnace: it depends
A variable-speed ECM motor at $1,000 to $1,600 on a 14-year-old 95 percent furnace is right at the line. If the heat exchanger inspects clean and the board has no fault history, repair. If the tech finds a second problem, replace.
Control board: usually repair under 15, replace over
$500 to $1,200. Boards fail from heat and power events, not from age alone, so a board on a 12-year-old furnace is worth doing. On a 19-year-old furnace it is the first of several.
Ignitors, sensors, switches: always repair
$150 to $400. These are consumables. A 22-year-old furnace with a bad ignitor and a clean exchanger gets the $200 ignitor and another winter, and you plan the replacement for spring when prices and schedules are softer.
Things that push toward replacing early
- Oversizing. A furnace that has short cycled its whole life is wearing out faster than its age suggests and never heated the house evenly. Arvada has a lot of these because the altitude derate was skipped.
- An 80 percent furnace and a plan to add or replace AC. The variable-speed blower in a new furnace improves the AC, matched equipment carries longer warranties, and a cold-climate heat pump replaces both with the largest rebate stack in Colorado.
- Selling in the next two years. A new, permitted furnace is a clean line on the inspection report. A 20-year-old one becomes a negotiation.
- Gas bills that climbed. A 20-year-old 80 percent furnace that has drifted to 70 percent is burning money that a 96 percent furnace would not.
Things that push toward repairing
- The furnace is under 12, the exchanger is clean, and the repair is a single known part.
- You are moving within a year and the repair gets you there.
- The venting run for a condensing furnace would be long and expensive in your house, and a same-efficiency swap is not much of an upgrade.
How the decision gets made here
On any repair over $500 on a furnace over 12 years old, the tech quotes the repair and a replacement side by side, in writing, on the same visit. The replacement quote includes the load calculation, the rebates you qualify for, and the venting situation. The diagnostic fee is credited to whichever one you choose. No pressure either direction; the numbers do the arguing.
Not sure how old the furnace is? Send a photo of the sticker through the photo quote. The serial number gives the manufacture date, and the tech will tell you which side of the line you are on before anyone comes out.