What Changed on January 1, 2026, and What Didn't
If you've heard talk of a furnace “deadline” in Colorado, you're not imagining things, but the details have gotten twisted along the way. HB23-1161 took effect January 1, 2026, and it changes what new gas furnaces contractors can sell and install in this state. It does not require you to replace the furnace already running in your house.
Homeowners across Castle Rock and the South Metro area have been calling Rock Plumbing, Heating, Air & Electrical asking whether they're now out of compliance or facing a fine. They’re not. HB23-1161 applies to new equipment sold or installed after January 1, 2026, not to a system that was already in place before that date. This law doesn't require an inspection, and there’s no penalty for owning a furnace that predates it.
What HB23-1161 Requires
HB23-1161 is a Colorado law passed in 2023 that sets new emissions and efficiency requirements for gas furnaces. As of January 1, 2026, any new gas furnace sold or installed in Colorado must meet one of two standards: Ultra-Low NOx or ENERGY STAR certification. That requirement applies to manufacturers, distributors, and contractors installing new equipment, not to homeowners who already have a furnace running.
The law doesn't apply to existing systems at all. If your furnace was installed before January 1, 2026, it keeps running as it has, with no retrofit and no penalty under this regulation.
For a straight answer about how this law affects the specific furnace in your home, call (720) 410-5239 or reach out online to schedule a system assessment.
Ultra-Low NOx and ENERGY STAR: The Two Paths to a Compliant Furnace
Ultra-Low NOx (ULN) refers to a limit on nitrogen oxide, a byproduct released when a furnace burns fuel at high heat. A ULN-compliant furnace can't exceed 14 nanograms of NOx per joule of heat output. That means a meaningfully cleaner burn than older standard-efficiency models produce.
ENERGY STAR is a U.S. EPA and Department of Energy program that certifies high-efficiency equipment. Colorado falls in the ENERGY STAR North region, where the minimum efficiency rating, AFUE (annual fuel utilization efficiency), is 95% through July 30, 2026, and rises to 97% AFUE starting July 31, 2026.
A new furnace only needs to clear one of these two standards, not both, which is why your installer has options depending on your home and your budget.
What This Means When You're Ready to Replace Your Furnace
Your current system isn't affected, but when you do eventually replace it, whether that's a planned upgrade or a furnace that fails on a January morning, the models available for a new install will be Ultra-Low NOx or ENERGY STAR compliant.
The following is what a compliant replacement changes for a home, and what it doesn't:
- Gas heat stays on the table – Compliant gas furnaces are already being installed across Colorado, so the law changes which models qualify, not whether gas heating is allowed.
- Fewer entry-level options – Some of the lowest-cost standard-efficiency furnaces no longer qualify for new installation, so quotes will lean toward higher-efficiency equipment.
- Altitude still matters – At Castle Rock's elevation, a new furnace still needs the correct combustion setup for thinner air, regardless of which compliance path it meets.
Our background-checked technicians walk you through which compliant models fit your home before you commit.
Why Planning Your Furnace Replacement Now Makes Sense
A furnace that fails in February gives you an afternoon to decide. A furnace you're already thinking about gives you weeks to compare options, check financing, and look into rebates. If you'd rather choose your next furnace than have a breakdown choose it for you, planning makes that possible.
Depending on the model, replacing proactively can open the door to utility rebates through providers such as Xcel Energy, along with applicable tax credits. We'll walk you through which programs apply at your assessment, and financing is available for larger projects.
Schedule a furnace assessment before you need one, and know your compliant Low NOx furnace options in advance.
Frequently Asked Questions About Colorado's Low NOx Furnace Law
The following are the questions we hear most often about the 2026 furnace standards. If your situation isn't covered here, contact us, and we'll walk through it with you.
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No. HB23-1161 sets emissions and efficiency requirements for new gas furnaces. It doesn't ban gas heating. Compliant gas furnaces are already being installed across the state, and gas heat remains a normal choice for a new installation.
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No. The law applies to new equipment sold or installed after January 1, 2026. If your furnace was already in place before that date, you can keep using it with no penalty and no deadline attached to this regulation.
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Yes. You'll be choosing from furnaces that meet Ultra-Low NOx or ENERGY STAR standards instead of every model that existed before, but gas furnace installation is still standard practice in Colorado.
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The replacement furnace your contractor installs must meet Ultra-Low NOx or ENERGY STAR requirements. That's why it helps to know your options before an emergency forces a same-day decision.
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You only need one. Ultra-Low NOx and ENERGY STAR are separate compliance paths, and a new furnace must meet just one to be installed legally. Your installer can help you choose the right option for your home.