Colorado homeowners have had a lot to keep straight about the state’s new furnace rules this year. Just when things felt settled, a new detail has come up: as of July 31, 2026, Colorado’s ENERGY STAR efficiency requirement for gas furnaces has increased.
While it doesn’t take gas heating off the table, and it doesn’t mean you need to replace a furnace that’s currently working fine in your Denver Metro home, it does change what a new furnace must meet to qualify.
Here’s a quick look at the update and what it actually means if you’re in the market for a new system.
A Quick Recap of HB23-1161
Colorado’s House Bill 23-1161 has been the law of the land since January 1, 2026. It requires that any new gas furnace installed in the state meet one of two compliance paths: ENERGY STAR certification or Ultra-Low NOx (ULN) status.
You only need to satisfy one of those compliance paths and nothing about the law forces you to replace equipment you already have installed.
The July 31 Change, Explained
ENERGY STAR is a federal program run jointly by the EPA and DOE that flags equipment meeting high efficiency benchmarks, and Colorado sits in the program’s North region. For the first several months of 2026, from January 1 through July 30, a gas furnace only needed to hit 95% AFUE (annual fuel utilization efficiency) to qualify under the ENERGY STAR path. That number moved on July 31, 2026, to 97% AFUE.
So starting July 31, any new furnace going the ENERGY STAR route needs to reach 97% efficiency, not 95%, to count as compliant.
The Ultra-Low NOx path hasn’t budged. A furnace might still qualify by keeping nitrogen oxide emissions at or below 14 ng/J, and that remains a fully separate, equally valid way to meet the law. If a unit doesn’t clear the new AFUE threshold, ULN compliance is still on the table.
What It Means If You’re Shopping for a New Furnace
Practically speaking, the lineup of ENERGY STAR-qualifying furnaces has narrowed toward higher-efficiency equipment. That’s not something to worry over. Compliant furnaces, on either the ENERGY STAR or ULN path, are still on the market across a range of budgets and features. The part that matters is having an installer who’s current on the requirements and can tell you which units actually qualify before you commit to one.
And if your furnace is running fine right now, none of this changes anything for you. There’s no requirement to replace equipment based on this update alone.
Absolute Stays Ahead of Colorado’s Furnace Rules So You Don’t Have To
HB23-1161 and now this AFUE increase have made for a moving target this year, and it’s easy to lose track of which numbers apply and when. Our team at Absolute Plumbing, Electrical, Heating & Air keeps up with the current standards across the Denver Metro area, whether you’re planning ahead for a replacement or dealing with a furnace that quit without warning.
Call us at (720) 807-5715 or schedule online, and we’ll walk you through what qualifies for your home. For more background on the law, check out our related posts on what to do now that HB23-1161 is in effect and what happens if you missed the January 1 deadline.
This article is provided for general informational purposes and is not legal advice. For questions about how HB23-1161 applies to your specific situation, refer to the official bill text or consult a licensed professional.