Effective January 1, Colorado has implemented a statewide requirement that significantly restricts which residential gas furnaces and water heaters can be sold in the state. Under the new rule, newly manufactured residential gas furnaces and water heaters offered for sale in Colorado must either meet ultra-low nitrogen oxides (NOx) emissions thresholds or comply with the most recent Energy Star standards. Equipment already in inventory as of January 1 may still be sold, but all new products entering the Colorado market must meet the new criteria.
Nationwide implications beyond Colorado
While ultra-low NOx requirements have existed for years in select local air quality districts, most notably in parts of California, Colorado is the first state to apply such a standard statewide to residential gas furnaces. That shift marks a meaningful escalation in how emissions policy is being applied to home heating equipment and sets a precedent that could spread to other states.
Breaking down the ultra-low NOx furnace rule’s origins
The rule stems from legislation adopted in 2023 that directed the state to establish new efficiency and emissions standards for a range of appliances sold in Colorado, including furnaces and water heaters. The law prohibits the manufacture, distribution, sale, or lease of new fan-type central furnaces or water heaters that do not meet the prescribed emissions limits or Energy Star requirements.
Civil penalties can reach up to $2,000 per violation, with aggregate caps set in statute. The enforcement structure places compliance responsibility on manufacturers, distributors, and sellers.
How ultra-low NOx requirements affect contractors and homeowners
In practice, ultra-low NOx mandates can operate as a functional restriction on gas furnaces, even when they are not described as bans. Ultra-low NOx equipment typically carries higher costs, fewer model options, and tighter supply constraints. In many markets, this limits contractors’ ability to offer a full range of solutions.
This leads to unintended consequences. For instance, when gas backup options are effectively removed from the table, homeowners may be pushed into all-electric configurations that are not well-suited to their homes or geography. Oversized heat pumps, electric resistance backup, and added dehumidification are often required to maintain adequate comfort and performance. This means increased upfront costs, higher utility bills, and unnecessary strain on the power grid.
Ironically, policies intended to accelerate the transition to cleaner technologies can instead encourage homeowners to delay replacement altogether. Faced with higher prices or fewer options, some consumers choose to keep older, higher-emitting equipment operating longer than intended.
Protecting fuel and technology choice is one of ACCA’s top policy priorities for 2025-26. Read more about our position and advocacy efforts here.
A broader pattern emerging at the state and local level
Colorado’s action is not an isolated development. For more than a decade, several local air quality management districts in California have adopted ultra-low NOx requirements for residential gas furnaces and water heaters. More recently, some jurisdictions have moved beyond ultra-low NOx standards toward zero-NOx requirements, effectively eliminating combustion-based options for certain applications.
Several states are now evaluating similar appliance emissions standards as part of broader climate, air quality, or building decarbonization strategies — some through state environmental agencies, others through energy offices or building code processes. Many of these policies are being developed with limited input from contractors and insufficient attention to industry realities, climate variation, housing stock, and grid readiness.
For contractors, this evolving landscape underscores the need for vigilance, as these requirements are quickly becoming state-level policy tools with little advance notice.
The post Colorado’s ultra-low NOx furnace rule signals a new threat to fuel choice appeared first on ACCA HVAC Blog.