Should I Replace My Gas Furnace with an Ultra-Low NOx Furnace?
If you live in the Bay Area and your gas furnace is nearing the end of its life, you may have already been told that your only legal replacement option is an ultra-low NOx (ULN) furnace. But before you make that investment, it's worth asking: Is an ultra-low NOx furnace really the best path forward in 2025?
The answer is complicated—and it depends on how long you plan to stay in your home, your comfort with electric alternatives, and your willingness to install something that's already on its way out.
What Is an Ultra-Low NOx Furnace?
Ultra-low NOx furnaces are designed to emit fewer nitrogen oxides (NOx), a byproduct of combustion that contributes to smog and poor air quality. California air districts like BAAQMD (Bay Area Air Quality Management District) and SCAQMD (Southern California Air Quality Management District) now require ULN furnaces for nearly all permitted installations. These systems limit emissions to under 14 nanograms per joule.
At face value, they seem like a cleaner, greener version of traditional gas furnaces. And they are. But here's the catch:
They’re being phased out too.
The Bigger Push: Zero NOx by 2029
The real long-term goal in the Bay Area isn’t just low emissions—it’s zero emissions. That means no combustion at all. Starting in 2029, BAAQMD will no longer allow the replacement of gas furnaces, including ultra-low NOx models. Instead, all new installations will need to be fully electric, such as heat pump systems.
So, what happens if you install a ULN furnace today?
In just 4 years, you won’t be able to legally replace it with another gas unit.
If it fails after 2029, you’ll be required to switch to an electric system.
Parts and support for ULN models may start drying up fast once the industry shifts focus to electric-only systems.
In other words, ULN is a short-term fix for a long-term policy shift.
A Real-World Example: David in San Francisco, CA
David owns a 1,600 sq ft home in San Francisco. His 25-year-old gas furnace stopped working last month. He called us hoping for a straightforward gas furnace replacement. When we explained that, under Bay Area regulations, he’s now required to install an ultra-low NOx model, he was hesitant.
David had heard about heat pumps but didn’t want to switch. He was concerned about cost, electrical upgrades, and performance during cold snaps. So, he agreed to install a ULN furnace—mainly because it let him avoid a bigger commitment right now.
But we had to be honest with him:
“David, this furnace may work fine for the next 10–15 years. But if it breaks down in 2029 or later, there’s a chance you won’t be allowed to repair or replace it with another gas system. If you plan to stay in this home long-term, it may be smarter to consider electrification now, while incentives are still strong.”
David appreciated the transparency—and while he still went with the ULN unit, he did so knowing it wasn’t a future-proof decision.
Our Take: ULN Is a Stopgap, Not a Long-Term Solution
If you're looking for a safe, forward-looking investment, a heat pump is the better option. It aligns with the 2029 zero-NOx mandate, takes advantage of current rebate programs, and future-proofs your HVAC system.
But we understand not everyone is ready to make that leap today. If you do opt for a ULN furnace:
Make sure your installer explains the regulatory roadmap ahead
Ask about the availability of parts and support post-2029
Plan financially for a second transition to electric if you stay in the home long-term
Final Thoughts
Ultra-low NOx furnaces may be legally compliant today—but they are not a permanent solution. The Bay Area’s shift toward zero NOx is real and imminent. Whether you make the transition now or later, the writing is on the wall: the future of home heating is electric.
Have questions or want to discuss whether a heat pump is right for your home? Contact us. We're happy to walk you through the pros, cons, and cost implications of each option—no pressure, just facts.
