Cost
What a new furnace costs
A typical new furnace runs about $2,800 to $6,800 installed, with a national average around $4,700. Gas furnaces range from about $3,800 to $10,000 depending on the brand, efficiency and how much ductwork and venting needs to change. Permits usually add a few hundred dollars or more.
National figures from Angi via Bob Vila (2024). Thornton quotes vary with house size, efficiency and venting. Ask for an itemized written quote.
| What drives the price | Why it matters |
|---|---|
| Efficiency (AFUE) | Standard 80% furnaces cost less up front. 95%+ furnaces save gas but need PVC venting and a condensate drain. |
| Size | A properly sized furnace (based on a load calculation, not the old unit's label) runs quieter and lasts longer. |
| Venting and ductwork | Switching to high efficiency, or fixing undersized ducts, adds labor. |
| Permit and inspection | Required for replacements. Your contractor should pull it. |
Repair or replace? A rule of thumb
- The furnace is 15+ years old and needs a major repair.
- The repair costs more than a third of a new furnace.
- You've had two or more repairs in the last two winters.
- The technician found a cracked heat exchanger or carbon monoxide concerns.
If two or more of those apply, a replacement quote is worth getting.
Consider a heat pump while you're at it
If your A/C is old too, a cold-climate heat pump can replace both, often paired with a gas furnace as backup. Colorado offers a heat pump tax credit that installers pass on as a discount. See 2026 heat pump incentives.
Questions
Good to know
How long do furnaces last in Colorado?
Most furnaces last about 15 to 30 years, depending on how well they're maintained. Many Thornton homes still run original furnaces from the 1990s or earlier.
Do I need a permit to replace a furnace in Thornton?
Furnace replacement generally requires a permit, and the contractor should pull it. A licensed Thornton contractor will handle the permit and inspection.
Should I replace my A/C at the same time?
If your A/C is also over 12 to 15 years old, replacing both together usually costs less than doing them separately and makes sure the two are matched. It's also the moment to consider a heat pump.
How do you choose companies?
We only work with locally owned companies that hold a current City of Thornton contractor license, carry insurance and have strong, recent Google reviews. If a company stops meeting that bar, we stop sending them customers.
Who are you, and is this free?
Thornton Home Pros is a local referral service, not a contractor. It's free for you: the company we connect you with pays us a referral fee. All quotes, work and warranties come directly from that company.
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