Oxidizer EPA Test Methods

A Quick-Reference Guide to Stack Testing for Oxidizer Compliance

Once your RTO, catalytic oxidizer, or thermal oxidizer is installed and running, the next question is usually: how do we prove it's destroying VOCs at the rate our permit requires? That's where EPA reference test methods come in.

These standardized procedures, published under 40 CFR Part 60, Appendix A, are how stack testing contractors verify an oxidizer's performance: destruction efficiency, outlet emissions, capture effectiveness of the ductwork feeding it, and more. For most oxidizer applications, Method 25 or 25A (VOC destruction efficiency via FID) is the method your compliance test will center on, though certain applications, like bakery ovens, are often tested using Method 320 or Method 18 instead. Regulators use the results to confirm your system is meeting permit limits, and your compliance (or "DRE") test report will reference these methods by number.

Below is a summary of the test parameters most relevant to oxidizer systems and the ductwork, enclosures, and exhaust stacks that support them, along with the EPA method associated with each.

EPA Stack Test Methods for Oxidizers

These are the methods most directly tied to oxidizer performance and permit compliance, start here.

Test Parameter	EPA Reference Method
Determination of Volatile Organic Compounds (VOCs)	EPA Method 25 / 25A
Determination of Volatile Organic Compounds (VOCs) via FTIR, commonly used for bakery oven emissions	EPA Method 320
Determination of Gaseous Organic Compounds by Gas Chromatography, commonly used for bakery oven emissions	EPA Method 18
Determination of Permanent Total Enclosure (PTE)	EPA Method 204

Related Supporting Test Methods

These methods support the oxidizer-specific tests above, establishing flow, correcting results, or measuring PM where applicable, and are typically run as part of the same test event.

Test Parameter	EPA Reference Method
Sample and Velocity Traverse	EPA Method 1
Velocity and Volumetric Flow Rate (Q)	EPA Method 2
Determination of Oxygen (O2) and Carbon Dioxide (CO2)	EPA Method 3A
Determination of Moisture Content	EPA Method 4
Determination of Particulate Matter (PM)	EPA Method 5
Determination of Condensed Particulate Matter (PM)	EPA Method 202

What These Methods Measure on an Oxidizer System

Oxidizer-Specific Methods

Method 25 / 25A

Volatile Organic Compounds (VOCs)
The most commonly applied test method for oxidizer systems. A flame ionization detector (FID) measures total organic compounds, typically reported as propane, at both inlet and outlet to calculate destruction efficiency, the number most oxidizer permits are built around. Method 25A is the continuous FID version most often used for oxidizer DRE testing; Method 25 (an integrated bag sample analyzed as total gaseous non-methane organics) is sometimes specified instead, depending on the permit.

Methods 320 & 18

Bakery Oven Emissions Testing
Bakery oven exhaust is a common application for oxidizers, but its VOC profile, largely ethanol from fermentation, is often tested differently than a typical process stream. Method 320 (FTIR) and Method 18 (GC) are the reference methods most often specified for bakery oven emissions, since they can speciate and quantify ethanol and other compounds more precisely than a simple FID reading. If you're sizing or permitting an oxidizer for a bakery oven, expect your test plan to reference one of these methods rather than Method 25A alone.

Method 204

Permanent Total Enclosure (PTE)
Applies to the capture system (hoods, ductwork, building enclosures) feeding VOCs to your oxidizer, not the oxidizer itself. A passing PTE test confirms the enclosure captures emissions with no meaningful fugitive losses, which lets capture efficiency be assumed at 100% in your overall compliance calculation, often a deciding factor in ductwork and hood design.

Related Supporting Methods

Methods 1 & 2

Traverse Points, Velocity, and Flow Rate
Every oxidizer performance test starts here. Testers need accurate sampling locations and volumetric flow rate at both the oxidizer inlet and outlet stack to calculate destruction efficiency correctly; this is the foundation every other measurement in the test builds on. Your ductwork design needs to provide adequate straight-run and port access at both locations for a valid test.

Method 3A

Oxygen and Carbon Dioxide
Combustion in a thermal or catalytic oxidizer changes the O2 and CO2 balance between inlet and outlet gas. These readings correct VOC concentrations to a standard basis, so destruction efficiency and outlet emissions can be fairly compared against your permit limits regardless of dilution air, excess air firing, or heat recovery configuration.

Method 4

Moisture Content
Oxidation produces water vapor as a combustion byproduct, so outlet stack moisture is typically higher than inlet moisture. Method 4 quantifies this so flow rate and concentration results can be adjusted to a dry-gas basis; without it, an oxidizer's destruction efficiency numbers would be skewed.

Method 5

Particulate Matter (PM)
Relevant for oxidizer systems handling particulate-laden exhaust streams (coating operations, some food and rubber processes) or where a wet scrubber or filtration system is installed upstream or downstream of the oxidizer. Uses an isokinetic sampling train to capture filterable PM directly from the stack.

Method 202

Condensable Particulate Matter
Measures the PM that forms as oxidizer exhaust cools after leaving the stack, increasingly relevant as PM2.5 and condensable PM limits show up in RTO and catalytic oxidizer permits, particularly for coating and food processing applications.

Why This Matters for Your Oxidizer System

If you're specifying, permitting, or operating an oxidizer, or the ductwork, enclosures, and heat recovery equipment around it, understanding which test methods apply helps you:

Anticipate what a destruction efficiency (DRE) test will actually measure at your inlet and outlet
Design ductwork with the sample ports, straight-run, and access a testing contractor needs for a valid Method 1/2 traverse
Account for how heat recovery, dilution air, or upstream particulate/scrubbing equipment can affect O2, moisture, and PM results
Communicate more effectively with your stack testing contractor and regulatory agency during system design, not just at test time

For a complete list of EPA test methods, visit EPA's Air Emission Measurement Center.

Have Questions About Compliance Testing?

CPI designs oxidizers, ductwork, and heat recovery systems with compliance testing in mind from the start, the right sample port locations, straight-run for accurate traverses, and performance margins built in to hit destruction efficiency targets with confidence.