UL 2998: What "Zero Ozone Certified" Actually Verifies
October 7, 2026
UL 2998 verifies that an air cleaner’s measured ozone emissions stay at or below 0.005 ppm (5 ppb). That limit is ten times stricter than California’s CARB limit of 0.050 ppm.
UL 2998 checks ozone only. It doesn’t test how well a device cleans the air, and it isn’t an overall safety certification.
- UL 2998: 0.005 ppm limit. Voluntary, third-party validation.
- CARB: 0.050 ppm limit. Mandatory for many devices sold in California.
- Pleated MERV 8, 11 & 13 filters: No ozone-generating mechanism, so they generally don’t need UL 2998.
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Shop Pleated Air FiltersA lower limit means a stricter standard.
Mandatory for many devices sold in California
Voluntary, independently tested and re-tested at least every three years
What a UL 2998 result tells you
Passive pleated filters trap particles mechanically. There’s no ozone-generating process involved.
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A "zero ozone certified" label sounds reassuring on an air purifier box, but the claim has a precise, narrow meaning. It tells you something about emissions, not performance. If you're comparing air-cleaning technologies, including ionizers, UV systems, and standard pleated filters, understanding what UL 2998 actually tests (and what it doesn't) will help you make a more informed choice for your home.
TL;DR: What Does UL 2998 Verify?
UL 2998 verifies one thing: an air cleaner's measured ozone emissions fall at or below 0.005 ppm (5 ppb) under UL Solutions' standardized test protocol. It says nothing about how effectively the device removes dust, allergens, or pathogens from the air, and it is not a general product safety certification.
Key Takeaways
UL 2998's ozone threshold, 0.005 ppm, is ten times stricter than the California Air Resources Board's (CARB) 0.050 ppm limit for regulated electronic air cleaners.
UL 2998 validates ozone emissions only. It does not assess air-cleaning effectiveness or overall product safety.
Passive pleated MERV filters, including Filterbuy's MERV 8, 11, and 13 filters, don't use an active ozone-generating mechanism and generally don't need UL 2998 validation.
Ionizers, electrostatic precipitators, some UV systems, photocatalytic oxidation (PCO) devices, and ozone generators are the technologies most likely to produce ozone.
What Is UL 2998 Certification?
UL 2998, formally known as the Environmental Claim Validation Procedure for Zero Ozone Emissions from Air Cleaners, is a program run by UL Solutions. It was created to give manufacturers a way to independently verify that their air-cleaning devices stay below a stringent ozone threshold: 0.005 ppm (5 ppb).
UL Solutions describes this figure as "the most stringent criteria available today," noting it represents one-tenth of the 0.050 ppm regulatory requirement that agencies like CARB apply to many electronic air cleaners. The program covers both standalone units, such as electrostatic air cleaners and electronic air purifiers, and duct-mounted devices like ionizers or UV lighting systems.
Products that pass are tested at least every three years, with surveillance audits in between to confirm continued compliance as materials or manufacturing processes change.
Does UL 2998 Mean Absolutely No Ozone?
Not literally. "Zero ozone" under UL 2998 doesn't mean the complete absence of ozone molecules. It means the device's measured ozone concentration falls at or below the program's 5 ppb quantifiable limit of detection under standardized test conditions. In practical terms, this is as close to zero as current testing can reliably measure, but it's a threshold, not an absolute.
How Does UL 2998 Zero Ozone Testing Work?
UL Solutions tests devices in a controlled chamber environment and measures ozone output against the 0.005 ppm limit. Products that qualify may display the UL Environmental Claim Validation (ECV) badge on packaging and marketing materials, signaling to shoppers that an independent third party verified the ozone claim rather than the manufacturer alone.
What Happens After a Product Passes?
Certification isn't a one-time event. UL Solutions re-tests validated products at least every three years and conducts surveillance audits during the years in between. This ongoing oversight matters because changes to a product's internal components or manufacturing process can alter its ozone output over time. Validated products are also listed on UL's SPOT Product Guide, a free online tool that lets buyers search for certified devices by category or manufacturer.
UL 867 vs. UL 2998: What's the Difference?
UL 867 is a safety standard for electrostatic air cleaners. It covers broader product safety requirements and permits a higher allowable ozone limit than UL 2998. Many regulatory bodies, including CARB, use testing methods referenced in UL 867 (specifically Section 40) to confirm devices meet the 0.050 ppm regulatory ceiling.
UL 2998, by contrast, is a narrower, voluntary validation focused exclusively on ozone emissions, set at a far stricter 0.005 ppm threshold.
Does Meeting UL 867 Mean a Device Is Zero Ozone Certified?
No. A device can comply with UL 867's safety and ozone provisions (staying under 0.050 ppm) without ever being tested against UL 2998's stricter 0.005 ppm benchmark. Meeting UL 867 confirms general electrical safety and compliance with the higher regulatory ozone limit. It doesn't confirm the "zero ozone" validation that UL 2998 represents.
UL 2998 vs. CARB Certification: What's the Difference?
CARB certification and UL 2998 validation both address ozone, but they serve different purposes and use different thresholds.
CARB requires most indoor air cleaning devices sold in California, including many electronic in-duct air cleaners, to be certified as producing no more than 0.050 ppm of ozone, as detailed in CARB's Regulation for Limiting Ozone Emissions from Air Cleaning Devices. This is a mandatory regulatory requirement in California. UL 2998 is a voluntary, third-party validation set at a far lower 0.005 ppm limit.
Comparison Table
Can an Air Cleaner Be CARB Certified Without UL 2998?
Yes. CARB certification only requires ozone emissions at or below 0.050 ppm. A device can meet that threshold and be sold legally in California without ever pursuing the stricter UL 2998 validation.
Can a Product Have UL 2998 Validation but Not CARB Certification?
Yes. UL 2998 is a voluntary ozone-emissions validation, not a substitute for CARB's certification process, which includes additional requirements such as electrical safety testing and labeling rules under California's regulation. A manufacturer could validate ozone emissions through UL 2998 while separately pursuing (or not pursuing) CARB certification.
Does CARB Certification Mean an Air Purifier Is Ozone-Free?
No. CARB certification confirms a device stays at or below 0.050 ppm, which is ten times the UL 2998 "zero ozone" threshold. A CARB-certified device can still emit measurable ozone, just below the regulatory ceiling.
Why Does Ozone From Air Cleaners Matter?
Ozone is a reactive gas that can irritate the respiratory system even at relatively low concentrations. According to the U.S. EPA's guidance on ozone generators sold as air cleaners, the agency states plainly that ozone generators should not be used in occupied spaces, and that no federal agency has approved these devices for that purpose.
Can Ozone Actually Clean Indoor Air?
Not effectively, according to the EPA. The agency's guidance states that at concentrations that don't exceed public health standards, ozone is not effective at removing many indoor pollutants, including some odor-causing chemicals and biological contaminants like viruses, bacteria, and mold. In other words, even where ozone emissions stay within accepted limits, there's limited evidence it meaningfully improves air quality, which is part of why independent ozone-emissions validation matters more than marketing claims.
Which Air-Cleaning Technologies Can Produce Ozone?
Several air-cleaning technologies carry the potential to produce ozone as a byproduct of how they operate: ionizers, electrostatic precipitators, some UV systems, photocatalytic oxidation (PCO) devices, and dedicated ozone generators. Passive pleated filters, which rely on physical fiber media to trap particles rather than an active electrical or photochemical process, are not on this list.
Do Ionizers Produce Ozone?
Ionizers can produce ozone because they disperse charged ions into the air, a process that, depending on design, can generate ozone as a byproduct. This is precisely why the EPA recommends that devices using bipolar ionization technology meet UL 2998 standard certification.
Do UV HVAC Lights Produce Ozone?
Some do, depending on the lamp's wavelength. UV light below roughly 200nm, especially the 185nm line found in many mercury lamps, splits oxygen molecules and creates ozone, while the 254nm germicidal line doesn't. Lamps built with doped quartz glass block the 185nm line while still passing the germicidal 254nm wavelength. For a full breakdown of how to check whether a specific UV lamp produces ozone, see Filterbuy's guide to whether HVAC UV lights produce ozone.
Do HVAC Air Filters Need UL 2998 Certification?
Generally, no. Passive pleated filters, including Filterbuy's MERV 8, MERV 11, and MERV 13 filters, don't rely on an active ozone-generating mechanism. They trap particles through mechanical filtration, forcing air through layers of pleated fiber media, rather than through electrical charge, ionization, or ultraviolet light. Because there's no ozone-producing process involved, these filters generally don't require UL 2998 validation.
Can Electrostatically Charged Pleated Filters Produce Ozone?
Some pleated filters use electrostatically charged fibers to attract particles, but this is distinct from the active electrical processes used in electrostatic precipitators or ionizers. The electrostatic charge in these filters is typically built into the fiber material itself during manufacturing, not generated by an ongoing electrical current running through the device during operation, which is the mechanism associated with ozone production.
How Do Filterbuy's Pleated Filters Work?
Filterbuy's MERV 8, MERV 11, and MERV 13 filters use pleated fiber media to physically capture dust, pollen, and other airborne particles as air passes through the HVAC system. Choose MERV 8 if you want reliable everyday dust and pollen capture with minimal airflow restriction. Choose MERV 11 if you want improved capture of smaller particles like pet dander and mold spores, a solid middle ground for most households. Choose MERV 13 if you want the highest practical filtration for a residential system, capturing finer particles including some bacteria and virus-carrying particles, provided your HVAC equipment can accommodate the added airflow resistance.
What Do Air Purifier Ozone Labels Actually Mean?
Not every label on an air purifier box tells you what you think it does. "UL Listed" refers to a general product safety listing and is not the same as a UL 2998 ozone result. "CARB certified" means the device meets the 0.050 ppm regulatory limit, not the stricter UL 2998 threshold. Phrases like "ozone free" or "zero ozone" without a named test or certifying body are marketing claims, not verified results. A genuine ozone validation should name the specific standard (UL 2998 or CARB) and, ideally, the exact model tested.
How to Verify a UL 2998 Zero Ozone Claim (Step-by-Step)
Look for the exact standard name. A credible claim will reference "UL 2998" or "ULE 2998" specifically, not just "UL Listed" or "tested for safety."
Check for the UL Environmental Claim Validation badge. Products that pass UL 2998 are entitled to display this badge on packaging and marketing materials.
Search the UL SPOT Product Guide. This free online tool lets you confirm whether a specific model has been validated.
Confirm the model number matches. Manufacturers sometimes validate one model in a product line; make sure the exact model you're considering was tested, not just a related product.
Cross-check CARB's certified devices list if relevant. For devices sold in California, you can also check CARB's list of certified air cleaning devices to see whether the product meets the separate 0.050 ppm regulatory standard.
Choose Effective Air Filtration Without Unnecessary Ozone Concerns
Once you understand the distinction between ozone-emissions validation and filtration effectiveness, the choice for whole-home air filtration becomes simpler. Passive pleated filters don't generate ozone in the first place, so there's no emissions claim to verify.
Filterbuy's MERV 8, MERV 11, and MERV 13 pleated filters are built for exactly this kind of straightforward, mechanical filtration, trapping dust, pollen, pet dander, and other particles without introducing ozone as a byproduct. You can browse Filterbuy's full lineup of pleated filters by MERV rating and size to find the right match for your HVAC system and household needs.
What to Look for Before You Buy
UL 2998 answers one specific question: does this air cleaner keep ozone emissions at or below 0.005 ppm? It doesn't tell you whether the device captures dust effectively, whether it's electrically safe, or whether it's the right fit for your home. CARB certification addresses a different, less strict ozone threshold tied to California's regulatory requirements, while UL 867 covers broader electrostatic air cleaner safety.
For passive pleated filters, including Filterbuy's MERV 8, MERV 11, and MERV 13 lines, the ozone question doesn't apply in the first place, since these filters rely on mechanical capture rather than an ozone-generating process. Understanding these distinctions helps you read labels accurately and choose air-cleaning products based on what they actually verify.
Frequently Asked Questions
Does UL 2998 certification mean a product is safe overall?
No. UL 2998 validates ozone emissions only, confirming they stay at or below 0.005 ppm. It does not evaluate electrical safety, structural integrity, or other aspects of overall product safety, which are typically addressed by separate standards like UL 867.
Is UL 2998 the same as CARB certification?
No. UL 2998 is a voluntary third-party validation with a 0.005 ppm ozone threshold. CARB certification is a mandatory regulatory requirement for many devices sold in California, with a less strict 0.050 ppm limit, roughly ten times higher than UL 2998's threshold.
Do pleated HVAC filters produce ozone?
Generally, no. Passive pleated filters, including Filterbuy's MERV 8, 11, and 13 filters, use mechanical fiber media to trap particles rather than an active ozone-generating mechanism, so they don't typically require UL 2998 validation.
What technologies are most likely to produce ozone in air cleaners?
Ionizers, electrostatic precipitators, some UV systems, photocatalytic oxidation (PCO) devices, and dedicated ozone generators carry the potential to produce ozone, depending on design. The EPA specifically recommends UL 2998 validation for devices using bipolar ionization technology.
Can ozone from an air cleaner actually improve indoor air quality?
The EPA states that at concentrations that don't exceed public health standards, ozone is not effective at removing many indoor pollutants, and the agency advises against using ozone generators in occupied spaces altogether.