How do I prepare for a stack test?

Start with your permit — confirm applicable methods, emission limits, and any advance notification requirements. From there: verify sampling port access and platform safety, confirm control equipment is operating normally, and document expected operating conditions during the test window. Some facilities also run pre-compliance or investigative testing beforehand to catch potential issues before the official test.

What happens if a test run is invalid?

It depends on the program. Under MACT (40 CFR Part 63), an invalid run can be replaced with an additional valid run with EPA Administrator approval. Under NSPS (40 CFR Part 60), compliance can be determined from two runs under specific circumstances, also with approval. One firm rule across both: if you run more than three runs, compliance must be based on the average of three consecutive valid runs — you can't average more than three to soften the result. All runs, including invalid ones, must still be reported.

What is the Electronic Reporting Tool (ERT)?

The ERT is the EPA's standardized application for preparing, transcribing, and submitting stationary source emissions test plans and reports. Reporting performance test data electronically using ERT is required by many federal subparts.

How are CEMS evaluations different from standard stack testing?

Standard stack testing measures specific pollutants to demonstrate compliance. A CEMS evaluation — specifically a Relative Accuracy Test Audit (RATA) — verifies that your continuous monitoring system is reading accurately by comparing it against a reference method. Linearity checks ensure the equipment stays within permissible limits over time. They serve different compliance functions and are often scheduled separately.

What are the penalties for missing a stack test deadline?

Missing a deadline can result in agency-imposed remediation requirements, unit shutdowns and lost production time, and reputational damage that affects your operating permit and community standing. If you test late without an approved extension, those results may be rejected — meaning you'll need to retest, extending the period of non-compliance and compounding costs.

The Facility Manager’s Guide to Stack Testing in 2026

Apr 16
3 min read

Updated: Apr 17

Stack testing — also called performance testing or source testing — is used to measure a facility's air emissions and verify compliance with emission limits established under the Clean Air Act (CAA).

A stack test tends to go one of two ways: planned and predictable, or compressed and reactive.

The difference comes down to coordination.

Delays in scheduling or execution can quickly lead to retesting costs, missed compliance deadlines, production disruptions, and increased regulatory risk. What starts as a timing issue can escalate into a much larger operational and financial impact.

This guide breaks down what stack testing is, when it is required, and how to execute it in a way that supports compliance and operations.

What Is Stack Testing?

Stack testing quantifies regulated air emissions at the source and is required to demonstrate compliance under federal programs, including NSPS, MACT, and NESHAP. It is used to demonstrate both initial and ongoing compliance under major federal programs, including New Source Performance Standards (NSPS) under 40 CFR Part 60, Acid Rain Program (Part 75, CEMS), National Emission Standards for Hazardous Air Pollutants (NESHAP) under 40 CFR Part 61, and Maximum Achievable Control Technology (MACT) standards under 40 CFR Part 63.

When Is Stack Testing Required?

Initial Compliance

New or modified sources typically face specific regulatory deadlines for completing an initial stack test:

NSPS (40 CFR Part 60): Within 180 days after initial startup, or 60 days after reaching maximum production rate
MACT (40 CFR Part 63): Notice of Compliance Status is typically due within 150 days for certain subparts

Ongoing Permit Requirements

Facilities with an Air Pollution Control Permit are commonly required to conduct periodic testing to demonstrate continuous compliance. Regulatory agencies can also require a test at their discretion, particularly when no continuous monitoring system exists or when previous results showed a narrow compliance margin.

Specific Operational Triggers

Stack testing is also required in these situations:

CEMS evaluations – Relative Accuracy Test Audits (RATA) and linearity checks to verify Continuous Emission Monitoring Systems
Rule changes – Updates to federal standards (Residual Risk and Technology Reviews, revised PM thresholds) can trigger new testing mandates
Information Collection Requests (ICRs) – EPA may require testing under CAA Section 114 to support new rulemaking

Engineering and Investigative Testing

Not all stack testing is regulation driven. Facilities routinely test for internal purposes — process optimization, control device evaluation, and emissions profiling for future planning.

Core Requirements for a Valid Stack Test

To produce defensible data, stack tests must meet strict regulatory criteria:

Representative Conditions: testing must reflect normal or worst-case operations
Run Structure: compliance is based on the average of three consecutive valid runs
Advance Regulatory Notification: These windows exist to give the regulatory agency the opportunity to observe.
- 30 days (Part 60, Part 61)
- 60 days (Part 63)
Data Integrity: invalid runs must be reported and may require replacement

Failure to meet these requirements can result in rejected data or required retesting.

How a Stack Test Works

Most compliance tests follow the same general structure:

Pre-test planning and method selection
Site-specific test plan development and agency notification
Equipment setup and calibration
Three test runs per emission point, with QA/QC checks
Final report preparation and submission

A straightforward test typically takes one to two days per emission point. Complex programs — multiple pollutants, restricted access points, or extended run times — take longer.

What Does a Stack Test Report Include?

The final report is the primary compliance document. A well-structured report should include:

Executive summary – What was tested, why, and how results compare to limits
Test program summary – Facility details, regulatory drivers, emission sources, control systems, and site-specific plans
Summary of results – Emissions data alongside operating conditions, compared directly to permit limits
Methodology – EPA reference methods used and any method-specific considerations
Appendices – Field data sheets, calibration records, process data, and example calculations

Stack testing is as much about scheduling coordination as it is about testing execution.

Facilities that align planning, operations, and testing early gain flexibility and reduce risk. Those that delay often face limited options and higher costs.

Alliance is the largest stack testing provider in the U.S.

Alliance Technical Group provides stack testing services nationwide, with accredited laboratories (NELAC, LELAP, TCEQ), on-site FTIR capabilities, and integrated field and analytical teams. Whether you're planning an initial compliance test or managing an ongoing permit requirement, we help you get through it with reliable data and fewer surprises.

If you are approaching a compliance deadline, the most important step is simple: Secure your test window early.

Schedule Your Stack Test Today →