If you’ve been trying to keep up with Colorado’s new furnace rules, you’re certainly not alone. Between HB23-1161 taking effect at the start of 2026 and now a fresh update to the ENERGY STAR requirements, it’s a lot to track.

Here’s the short version: as of January 1, 2026, new covered fan-type central furnaces sold or distributed in Colorado generally must meet the state’s NOx emissions standard or qualify for the ENERGY STAR compliance pathway.

This doesn’t change whether gas heating is available to you, and it doesn’t require you to replace a furnace you already own. Put simply, it changes what thresholds a new furnace has to hit to qualify under one of the two compliance paths.

Here’s what actually changed and what it means if you’re shopping for a new system.

Quick Recap: What HB23-1161 Has Always Required

Colorado passed HB23-1161 in 2023, and as of January 1, 2026, every new gas furnace installation in the state has to meet one of two standards: it needs to be either ENERGY STAR rated or Ultra-Low NOx (ULN) compliant. You only need to satisfy one path, not both, and none of this applies retroactively to furnaces already installed in your home. For the full rundown on what the law requires and what to do if you’re planning a replacement, take a look at our earlier post, what Colorado’s furnace law means for homeowners.

What Changed on July 31, 2026

This is the update worth knowing about. ENERGY STAR is a joint EPA/DOE program that recognizes high-efficiency equipment, and Colorado falls under its North region classification. From January 1 through July 30, 2026, the minimum ENERGY STAR rating for a compliant gas furnace in Colorado was 95% AFUE (annual fuel utilization efficiency). Effective July 31, 2026, that threshold increased to 97% AFUE.

Beginning July 31, 2026, a gas furnace in Colorado using the ENERGY STAR compliance pathway must meet the Version 5.0 requirements. For the U.S. North region, that means at least 97% AFUE.

The good news is that the Ultra-Low NOx path hasn’t changed at all. A ULN-compliant furnace still needs to keep nitrogen oxide emissions at or below 14 ng/J, and that option remains just as valid as it was before. If a furnace doesn’t clear the new 97% AFUE mark, it can still meet the law through the ULN standard instead.

What This Means for Homeowners Replacing a Furnace

If you’re in the market for a new furnace right now, the pool of ENERGY STAR-qualifying equipment has shifted toward higher-efficiency models. That’s not a reason for concern. Compliant furnaces, both ENERGY STAR and ULN, are still readily available across a range of price points and features. What matters most is working with an installer who knows the current requirements and can walk you through which options qualify for your home.

And again, if your existing furnace is running fine, this update doesn’t affect you. You’re not required to upgrade or replace anything based on this change.

R Buck Is Up to Date, So You Don’t Have to Be

R Buck Heating, Cooling, Plumbing & Electrical stays current on HB23-1161 and the latest AFUE update standards so you don’t have to sort through the regulatory details yourself, whether you’re planning ahead for a replacement or dealing with a furnace that’s given out unexpectedly. Our Pueblo and Colorado Springs technicians can walk you through which systems qualify and what makes sense for your home.

Call us today or schedule online to talk through your options. For more specifically about the law itself, see what homeowners should do now and what happens if you missed the deadline.

The content in this article is intended for general informational purposes only and should not be taken as legal advice. For guidance on how HB23-1161 applies to your particular situation, please review the official bill text or speak with a licensed professional.