Firewood Guide | Understanding Crib Wood, Cord Wood and the History of EPA Wood Stove Emissions Testing

Firewood comes in all shapes and sizes. Any firewood you would burn in your home is not what is currently used by the EPA for testing the efficiency of wood stoves. Crib wood is often used instead of the more common cord wood due to the variation of firewood throughout the world. In short, crib wood shows how clean a stove can burn. Cord wood shows how clean it will burn in a home.

What is Crib Wood?

Crib wood is for testing purposes only because it is consistently available. As defined by the EPA, “Crib wood is a specified configuration and quality of dimensional lumber and spacers, usually cut 2”x4” or 4”x4” lumber improve the repeatability of wood burning emissions test methods.”

What it is: Uniform dimensional lumber sticks, stacked in a precise pattern.
Fuel quality: Kiln-dried, identical size, very consistent.
Why it is used by the EPA for testing: Repeatable, easy for labs to control.
Downside: Burns cleaner and easier than real firewood.
Result: Often understates real-world smoke and emission.
Status: Still allowed, but less trusted today because it is not how homeowners burn at home.

What is Cord Wood?

Cord wood is real world firewood that you would actually use in your life. As defined by the EPA, “Cord wood, also called firewood, is what a typical homeowner uses, and is a more accurate measure of how a wood heater will perform in homes.”

What it is: Real split firewood (mixed species, sizes).
Fuel quality: Controlled moisture range (~16–20%), natural variability.
Why it is used by the EPA for testing: Matches how homeowners actually burn.
Downside: Harder to test consistently across labs. Same species and age of wood is near impossible to find in each testing lab location throughout the world.
Result: More realistic emissions data. Status: Allowed and preferred, though still being refined.

What is the history of EPA wood stove emission testing?

1) Pre-EPA era (before 1988)

No federal emissions limits. Smoke, creosote, and neighborhood complaints were common. Performance depended entirely on operator skill. Result: Public-health pressure forced regulation.

2) 1988–2014: EPA certification begins (crib wood only)

The Environmental Protection Agency introduced the first national standard. In 1988, the EPA set the first national smoke limits for new wood stoves, forcing manufacturers to prove in a lab that their stoves burned cleaner, which permanently improved how wood stoves are designed and built. Learn more about the New Source Performance Standards.

Test method: EPA Method 28

Fuel: Crib wood only (dimensional lumber)

Metric: Particulate matter (g/hr) Typical limits: ~7.5 → 4.5 g/hr

3) 2015 NSPS rewrite: realism added EPA overhauled NSPS Subpart AAA.

Major changes:

Introduced cord wood testing (Method 28R)
Created Phase 1 and Phase 2
Lowered emission caps
Cord wood was optional, not mandatory

Why? EPA acknowledged crib wood was not predicting real-world emissions.

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4) 2020 Phase 2: The Strictest Wood Burning Standard

National limit was tightened to 2.0 g/hr from 4.5 g/hr in 2020 as part of Phase 2. Cord wood was strongly encouraged. Many manufacturers voluntarily switched to cord wood to represent real world usage.

Learn more about EPA Certification Tests and the shift from crib wood to cord wood via NESCAUM.

Positive wood burning industry shifts:

Better firebox design
Better low-burn control
Cleaner real-world performance

5) 2023–2024: cord wood review and overall confusion

EPA observed some problems with cord wood testing. Things like lab-to-lab variability, fuel prep inconsistencies and enforcement risk made cord wood unrealistic long term.

Hear from Chris Neufeld of Blaze King >> Are Cord Wood Tested Stoves Going Away?

What did the EPA do?

Paused exclusive reliance on new 28R data
Reaffirmed that both crib and cord wood are allowed
Began refining cord-wood protocols

Real wood makes for a tougher, more real-world, honest test!

EPA testing wood stove efficiency impacts cost, availability and overall quality of wood stoves and wood fireplace inserts. What the government requires labs to use has changed over the years. From ventilation to fuel, everything can impact an EPA efficiency test result. In this case, what you need to know: Crib wood = perfect fake wood for the lab. Cord wood = real firewood like people actually use.

Buying a new wood stove or wood fireplace insert is a big decision. Learn more from the EPA >> Choosing the Right Wood-Burning Stove

Takeaways about Firewood and Wood Stove Testing for the Future: