Replacing Your Furnace in Colorado? What the New 97% AFUE Standard Means
Northern Colorado homeowners in search of a new furnace system have been sorting through a lot of information about the state’s new furnace requirements. Now, there’s an important update to know if you’re planning to replace your gas furnace: the ENERGY STAR® efficiency standard for installing new furnaces in Colorado’s northern climate zones, including the Denver metro area, increased on July 31, 2026.
The good news? This change does not mean gas heating is going away, nor does it require you to replace a furnace you already have. It simply changes which new gas furnace models can be installed under Colorado’s new regulations.
We created this guide to help simply explain the new change.
A Quick Recap of Colorado’s 2026 Furnace Requirements
Colorado passed HB23-1161 in 2023, establishing new requirements for gas furnace installations. Beginning January 1, 2026, newly installed gas furnaces had to meet one of two standards:
- They must either be ENERGY STAR-rated or
- Comply with the state’s Ultra-Low NOx (ULN) requirements.
These are alternative compliance paths for installations, meaning your new furnace only needs to meet one of the two standards, not both.
If you’re looking for more background on the law and Low NOx requirements, see our detailed Colorado HVAC Law 2026 page.
What Changed on July 31, 2026?
The big change involves the ENERGY STAR compliance path and those in Northern Colorado. From January 1 through July 30, 2026, the minimum ENERGY STAR requirement for newly installed furnaces in Colorado’s Northern region was 95% AFUE (annual fuel utilization efficiency). Effective July 31, 2026, the minimum increased to 97% AFUE.
This means any new gas furnace installed after July 31 must meet the updated 97% AFUE threshold if it is being used to satisfy the ENERGY STAR compliance path of the new state regulations.
If it does not have a 97% AFUE, the other compliance option remains available. A new furnace installation following the Ultra-Low NOx path must not exceed 14 nanograms of nitrogen oxide emissions per joule (14 ng/J).
You don’t need to become an HVAC expert to navigate this update or sort between which models meet which compliance path. You should work with an installer like Carbon Valley Heating, Air, Plumbing & Electrical who understands the current Colorado requirements and can identify equipment that qualifies.
FAQs About Colorado’s HVAC Law AFUE Changes
What Does 97% AFUE Mean?
AFUE stands for “annual fuel utilization efficiency.” It measures how efficiently a furnace converts fuel into heat over the course of a typical heating season. A higher AFUE percentage generally means more of the fuel’s energy is converted into usable heat.
The move from 95% to 97% may sound small and inconsequential for overall energy savings (and realistically, it is), but it matters when you’re comparing equipment because it changes which furnace models you can install under the ENERGY STAR path of Colorado’s 2026 HVAC law.
Do I Have to Replace My Existing Furnace?
No, this update to Colorado HB23-1161 does not require the replacement of existing furnace installations.
If your existing gas furnace is operating normally, you are not required to replace it simply because the efficiency standard changed. The updated requirements apply when a new gas furnace is installed.
Can I Still Install a Gas Furnace in Colorado?
Yes, compliant gas furnaces are still available and continue to be installed in Colorado. The updated rule changes which equipment qualifies; it does not eliminate gas heating as an option.
If you’re planning a Colorado gas furnace replacement, your Carbon Valley installer can help you compare qualifying equipment based on efficiency, system features, your home’s requirements, and your budget.
What Should Homeowners Do If They Need a New Furnace?
If you’re replacing a furnace today in Northern Colorado, the equipment options have shifted toward higher-efficiency models under the ENERGY STAR path. That doesn’t mean you need to panic or rush into a decision.
Instead, ask your Carbon Valley HVAC contractor:
- Does this furnace meet the current Colorado requirements?
- What is the furnace’s AFUE rating?
- Is it qualifying under the ENERGY STAR or Ultra-Low NOx path?
- Are there other compliant furnace replacement options that better fit my home and budget?
Our knowledgeable HVAC professionals can help you understand your options and make sure the equipment you select meets the requirements in effect.
Reach Out to the Firestone, CO, Furnace Experts
The minimum ENERGY STAR efficiency threshold for qualifying gas furnaces in Colorado’s North region increased from 95% to 97% AFUE, and the Ultra-Low NOx option remains available at 14 ng/J or less.
Simply put, Colorado’s furnace rules have become more specific on how efficient a new system must be. And if you already have a furnace in your home, you don’t need to replace it just because of this update.
For homeowners in Firestone, CO, or a surrounding area facing a furnace replacement, Carbon Valley can help you understand the current requirements and the qualifying models available to you. Call (720) 507-9924 or request service online to make an appointment through our website.
This article is provided for general informational purposes and is not legal advice. Furnace requirements can depend on the specific installation and applicable regulations. Consult a qualified HVAC professional for guidance on your individual situation.