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Emissions Testing: Why Do They Use Grams/Hour?

Q: It seems to me that grams/hour [the rating standard used in the US] doesn't make sense. The grams/kilo burned [the rating standard used in Europe] makes more sense, but still doesn't seem to tell us what we really need to know.  Why not use grams per btu?  That would allow us to compare the amount of pollution produced to the amount of heat produced.

Huck Rorick

Sweepy Hi Huck,

The European grams/kilo burned rating standard might be a little more intuitive, but is no more accurate than the US grams/hour standard.

During wood stove emissions testing, the initial weight of the test "charge" is recorded, and zero final weight (all fuel consumed) is used to define the fire duration end point. What that creates is, the WEIGHT of the fuel consumed and the duration of TIME it took for that to happen are equally valid benchmarks for use in determining particulate emissions ratios.

To illustrate, let's look at a fictional stove that burns a 10 kilogram charge in 5 hours, producing 20 grams of airborne particulates in the process.

In the US, that model would score a 4 grams/hr rating (20 grams / 5 hours).

In Europe, Australia and New Zealand, the same test results would be expressed as 2 grams/kilo (20 grams / 10 kilos).

As you can see, both rating techniques express the same test results, and both provide a concise and easy-to-grasp means to compare the emissions of one model to another.

That said, it is unfortunate that a single convention couldn't have been agreed upon, as European manufacturers who want to sell their products in the US must provide a grams/hr interpretation in their literature, and vice-versa.

Hey, how 'bout we approach both camps with your idea of converting to the Rorick system (grams/btu)? A 10 kilo charge contains, on average, 136,400 btus of extractable heat energy, so a stove that burned 10 kilos and produced 20 grams of airborne particulates would be rated at 0.000146628 grams/btu!

After further consideration, that number seems needlessly cumbersome for publishing, comparison and comprehension purposes, don't you think?

To read the actual text of the wood stove emissions regulations on the EPA's website, click here.

To read a brief history of the EPA wood stove emissions regulations, click here.

To view the EPA's list of wood stoves that have passed emissions testing, click here.

To read about our own real-world test of the new clean-burning technology, click here.




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