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Colorado's HB23-1161 changed which furnaces can be sold in Denver — and it's driving costs up 40–80%. Learn what the Ultra Low NOx law means for your next furnace replacement.
If you've shopped for a new furnace in Colorado recently, you may have already noticed the options look different and prices are higher. That's the direct result of Colorado House Bill 23-1161 — a law that took effect January 1, 2026, requiring all new gas furnaces sold or installed in Colorado to meet Ultra Low NOx (ULN) emission standards.
Here's the most important thing to understand upfront: this law did not eliminate 80% AFUE furnaces from the market. The Ultra Low NOx furnace is still an 80% furnace — same efficiency rating, same metal flue venting — but it uses a new burner design to dramatically reduce nitrogen oxide emissions. What's gone from Colorado is the standard, lower-cost 80% furnace that the rest of the country continues to use. In its place: ULN-compliant 80% models that are more expensive, available in fewer sizes, and manufactured by fewer brands. As an HVAC company serving the Denver Metro Area for over 16 years, our team at MoJo Home Services wants every Colorado homeowner to understand exactly what changed — and what it means for your next furnace replacement.
What Is Colorado's Ultra Low NOx Law (HB23-1161)?
Colorado House Bill 23-1161 was signed by Governor Polis in June 2023 and became enforceable on January 1, 2026. The law targets nitrogen oxide (NOx) emissions — a class of air pollutants produced by gas combustion that contribute to ozone formation and the respiratory health risks associated with Denver's notorious brown cloud inversions during cold winter months.
Under HB23-1161, any new gas furnace sold, supplied, or installed in Colorado after January 1, 2026 must either:
Meet Colorado's Ultra Low NOx emission limit of 14 nanograms per joule (ng/J), or
Be ENERGY STAR certified under the current EPA specification
In practice, this gives homeowners and contractors two paths when a furnace needs replacing. The first is a ULN-compliant 80% furnace — same efficiency as before, same metal flue venting, but with an updated low-NOx burner. The second is to upgrade to a 97% AFUE condensing furnace, which requires new PVC exhaust infrastructure but offers higher energy efficiency and qualifies for federal ENERGY STAR tax credits. Our team can walk you through which option makes more sense for your home's existing setup and budget.
Why Colorado Is Almost Alone — and Why That Creates a Supply Problem
Here's the part that surprises most Denver homeowners when we explain it: Colorado is one of the only jurisdictions in the entire country with this requirement. The South Coast Air Quality Management District in Southern California — covering Los Angeles and surrounding counties — has had similar Ultra Low NOx rules for several years. California's Bay Area Air Quality Management District is moving toward stricter requirements. But as a statewide mandate? Colorado stands nearly alone. No other U.S. state has enacted this requirement at the state level.
And that creates a serious market problem. Major appliance manufacturers — Carrier, Trane, Lennox, Rheem — design their production volumes around national demand. When a single state with just over 1% of the national population requires a specialty product that no other state has legislated, manufacturers have limited incentive to invest in full-scale production. The result:
Severely limited product selection. Ultra Low NOx compliant furnaces exist — but most manufacturers are not producing them in every BTU size or configuration. If your home's heating load calls for a specific size and that size isn't available in a ULN 80% model, you're faced with two choices: purchase a larger unit than your home actually requires, or upgrade to a 97% condensing furnace instead. Neither is the straightforward like-for-like swap homeowners are used to.
No economy or builder-grade options. Budget and entry-level brands have largely not invested in ULN product lines at all. Your choices are concentrated in mid-tier and premium brands — there is no lower-cost alternative for Colorado homeowners the way there is for buyers in the other 49 states.
Longer lead times. Ordering a specific ULN unit may mean waiting days or weeks rather than pulling from local distributor stock as was routine before 2026.
Significantly higher prices. Specialty manufacturing, lower production volumes, and concentrated Colorado demand have driven installed costs up 40% to 80% compared to pre-law pricing. A furnace that cost $4,500–$6,500 installed in 2024 may now run $7,000–$12,000 for a compliant replacement. This reflects real market constraints — not price gouging.
These dynamics will not normalize quickly. Until more states adopt similar requirements — building national manufacturing scale — or manufacturers make a larger commitment to the Colorado market, supply will remain tight and prices elevated.
What Changed for the 80% Furnace
The 80% AFUE gas furnace hasn't disappeared from Colorado — it's been redesigned. What changed is the emissions standard the burner must meet. As of January 1, 2026, any new 80% furnace sold or installed in Colorado must be an Ultra Low NOx compliant model — one that produces no more than 14 ng/J of nitrogen oxides. Achieving that requires new burner designs, tighter manufacturing tolerances, and engineering changes that add meaningful cost.
One important clarification: ULN 80% furnaces still use the same metal B-vent exhaust venting as the units they replace. Homeowners replacing an existing 80% furnace with a ULN 80% model do not need to modify or replace their existing venting infrastructure. The installation process is essentially the same — just with a more expensive unit and fewer brand and size options to choose from.
What cannot be sold or installed in Colorado any longer is the standard, conventional 80% furnace that remains widely available across the rest of the country. Those units exceed Colorado's 14 ng/J NOx limit and cannot be legally installed after January 1, 2026. Any contractor installing non-compliant equipment faces permitting violations and liability.
So in practical terms, when your furnace needs replacing, you now have two paths:
ULN 80% replacement: Same efficiency, same venting, compatible with your existing exhaust system. More expensive than the standard 80% and available in limited sizes and brands — but a straightforward swap if the right unit exists for your home's BTU requirements.
Upgrade to 97% condensing: Higher efficiency, qualifies for federal ENERGY STAR tax credits, but requires upgrading to new PVC exhaust infrastructure — an added cost and installation step that doesn't apply to the ULN 80% path.
Our NATE-certified technicians assess each home individually to determine which path makes more sense given your existing equipment, venting setup, and budget.
Who Needs to Act Now — Across All of Colorado
This law applies to every homeowner in Colorado — not just in certain cities or ZIP codes. Whether you're in Denver proper, the southern suburbs, the northern corridor, or anywhere across the Front Range, the same rules apply the moment your furnace needs replacing. The homeowners most urgently affected are those with:
Furnaces 15 years or older. Average furnace lifespan is 15–20 years with proper maintenance. At 15 years, you're statistically inside the replacement window. A proactive replacement — while you can plan, source equipment, and budget — is far better than a mid-winter emergency call when inventory is at its tightest.
Any aging standard 80% AFUE furnace. When this unit fails, there is no like-for-like replacement under current law. Understanding your options now — ULN 80% or 97% condensing — gives you time to make the right decision rather than taking whatever's available in an emergency.
Homeowners uncertain about their furnace's age or condition. Many homeowners don't know their furnace's exact age or efficiency rating. A quick assessment changes that — and knowing where you stand is the first step to planning ahead.
Denver's altitude adds another layer to every furnace selection. At 5,280 feet, combustion efficiency is reduced, and ULN-compliant furnaces need to be properly sized using Manual J load calculations — not rule-of-thumb BTU estimates. Our article on how Denver's elevation impacts HVAC performance explains why altitude-adjusted sizing matters on every Front Range installation.
How MoJo Home Services Is Navigating This Transition
We've spent the past two years building distributor relationships focused on ULN-compliant inventory and developing installation protocols for the new generation of compliant heating systems. Our NATE-certified technicians are fully trained on both ULN 80% installations and 97% condensing upgrades — including the venting, drain, and sizing considerations that differ between them.
Because ULN product availability is constrained, knowing what's in stock and what lead times look like before you commit matters more than ever. We check current distributor inventory as part of every estimate, so you're never surprised by a week-long wait in the middle of winter. We also size every installation using Manual J load calculations — critical at Denver's altitude, and especially important when the available ULN unit doesn't perfectly match your home's calculated heating load.
For an overview of the high-efficiency furnace options available in the current Denver market — including where the 97% condensing upgrade makes financial sense — see our guide on the top furnaces for Denver homes in 2026.
Your Denver Heating Partner Through the ULN Transition
Colorado's Ultra Low NOx law is in effect, the market has changed, and the dynamics around product availability and pricing are real. The homeowners who will navigate this most successfully are those who plan ahead — who assess their current equipment's age and condition now, understand what a compliant replacement will realistically cost, and make decisions on their schedule rather than in the middle of a system failure.
MoJo Home Services has been serving Denver Metro homeowners for over 16 years. We are NATE-certified, EPA-certified, and BBB-accredited — and we've made it our mission to guide customers through exactly these kinds of market transitions with honest advice, compliant installations, and no surprises on the final bill.
If you want to understand where your current system stands and what a ULN-compliant replacement would look like for your home, let's start that conversation before it becomes an emergency. Contact MoJo Home Services today to schedule a system assessment — we serve homeowners throughout Denver, Wheat Ridge, Lakewood, Aurora, Arvada, Westminster, Thornton, Englewood, and all of the surrounding Denver Metro Area.
Sources & References
Colorado General Assembly — HB23-1161: Environmental Standards For Appliances, 2023
KJCT8 News (Grand Junction) — New Colorado Law Requires Lower-Emission Furnaces Starting January 1, December 2025
Bay Area Air Quality Management District (BAAQMD) — Building Appliances Rule Implementation, 2023
Alpine Building Performance — Why Furnace Replacements Cost More in Colorado Starting in 2026, alpinebuildingperformance.com, February 2026
Air Conditioning Contractors of America (ACCA) — Manual J Residential Load Calculation, 8th Edition
Need a ULN-compliant furnace in Denver? MoJo Home Services provides expert installation of Ultra Low NOx certified heating equipment throughout the Denver Metro Area. Contact us at 4000 Newman St, Wheat Ridge, CO 80033 or call (720) 807-4050 for a free system assessment and installation quote.
Frequently Asked Questions
What is Colorado's Ultra Low NOx furnace law?
Colorado House Bill 23-1161, signed in 2023 and effective January 1, 2026, requires all new gas furnaces sold or installed in Colorado to meet Ultra Low NOx (ULN) emission standards — specifically, nitrogen oxide emissions no greater than 14 nanograms per joule (ng/J). The key distinction: the law didn't ban 80% AFUE furnaces. It changed which 80% furnaces can be sold. Ultra Low NOx compliant 80% models — with redesigned low-NOx burners — are still available in Colorado. What's no longer legal to install is the conventional, standard 80% furnace that continues to be sold everywhere else in the country.
Is Colorado the only state with this Ultra Low NOx law?
Colorado is one of the only jurisdictions in the country with a statewide Ultra Low NOx mandate for furnaces. The South Coast Air Quality Management District in Southern California has had similar NOx rules for several years, and California's Bay Area Air Quality Management District is moving toward stricter appliance requirements. But no other U.S. state has enacted this as a statewide law for furnaces. This geographic isolation — just over 1% of the national population — is the primary reason product supply is constrained and prices are significantly elevated in Colorado compared to national averages.
What are my two options when my furnace needs replacing under the new Colorado law?
When your furnace needs replacing in Colorado, you have two compliant paths. The first is a ULN 80% replacement: a furnace with the same 80% AFUE efficiency and the same metal B-vent exhaust venting as your existing unit — no venting changes required. It's more expensive than the standard 80% and available in fewer sizes and brands. The second option is to upgrade to a 97% AFUE condensing furnace: higher efficiency, qualifies for ENERGY STAR tax credits, but requires installing new PVC exhaust venting — an added cost and installation step not needed for the ULN 80% path. Our team assesses each home individually to determine which option fits your setup and budget best.
Does a ULN 80% furnace require new venting or exhaust changes?
No. Ultra Low NOx compliant 80% furnaces use the same metal B-vent exhaust venting as the standard 80% units they replace. If you're swapping an old 80% furnace for a new ULN 80% model, your existing venting infrastructure stays intact — no modifications needed. Venting changes only come into play if you choose to upgrade to a 97% AFUE condensing furnace, which vents through PVC pipe rather than a metal flue. Our technicians will clarify exactly what your specific installation requires before any work begins.
Why are furnace prices so much higher in Colorado right now?
Colorado's Ultra Low NOx requirement applies to just over 1% of the national population — one of the smallest markets in the country with this rule. Major manufacturers design production volumes for national demand, and building a specialty ULN product line at scale for one state requires investment they've been slow to make. The result: limited product selection, not every BTU size available, no economy brand options, longer lead times, and installed costs that are 40–80% higher than pre-law equivalents. A furnace that cost $4,500–$6,500 installed in 2024 may now run $7,000–$12,000. These constraints will persist until more states adopt similar rules or manufacturers increase their commitment to the Colorado market.
What if the right ULN furnace size isn't available for my home?
This is a real issue Colorado homeowners face. Because most manufacturers aren't producing ULN 80% furnaces in every BTU size, you may find that the size your home actually requires isn't currently available. In that situation, you have two options: purchase the next available size up (slightly oversized but compliant), or upgrade to a 97% AFUE condensing furnace, which is available in a wider range of configurations. Our team checks live distributor inventory during every estimate so we can give you accurate options based on what's actually in stock — not hypothetical availability.
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