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WOOD STOVE COMPARISON PAGE

Sorted By: EPA EMISSIONS RATING

To sort the table, click the column header (ie; Stove Dimensions, Shipping Weight, etc.)

 To visit (or return to) any stove's page, click its name in the chart above.

Note: Woodstove EPA emissions ratings don't tell the whole story.

A difference of a couple of grams or so in the emissions rating wouldn't be a good reason to choose one EPA approved woodstove over another. Great care is taken by the EPA testing laboratories to ensure that each test is as close as possible to the next (for example, identical nailed-together "charges" of pine wood are used in all tests), but uncontrollable factors such as atmospheric conditions and variables in personnel and testing equipment from one lab to another can affect the results of a given test burn. To compensate for these minor variances, the final EPA grams/hr rating is derived by averaging several monitored burns. As a result, differences of even a gram or two in the final emissions rating between one model and another are not considered significant (except, of course, by the manufacturer of the model that lucked out and got the lower rating).

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Q: Greetings,
I'm just beginning to educate myself on modern-day wood stoves (been using a Fisher for decades) and I've seen stoves online for example, where one has an efficiency rating of, say, 75% with emissions at 3.5 gm/hr., and another stove will have efficiency of 72% w/ emissions at 2.3. I can't make sense of that. Can you shed some light on how these calculations are derived?
Thank you
Roger

Hi Roger,

Thanks for the inquiry! A woodstove's heating efficiency rating doesn't correlate directly to its emissions rating. In fact, those numbers are arrived at in two different tests:

Emissions testing is performed in EPA-approved test labs using the EPA's prescribed protocol. When testing for emissions, a nailed-together "charge" of kiln-dried Pine is burned, and the particulate matter in the exhaust is measured throughout the duration of several fires at various draft control settings. In this way, an average grams/hour particulate emissions rating is derived. Heating efficiency is not measured during EPA emissions testing.

Heating Efficiency testing is performed using full loads of seasoned cordwood, and is designed to measure how much of the heat value contained in the wood is extracted and delivered into the living space. When testing for heating efficiency, the following criteria are examined:

Extraction Efficiency: the load is weighed going in, and the particulate emissions and ashes are weighed after the fire to determine how effectively a given firebox design breaks down the fuel to extract the available heat.

Heat Transfer Efficiency: this testing is performed in calorimeter rooms equipped with temperature sensors. Similar temperature sensors are installed in the exhaust flue. The degree changes in the room and flue are monitored for the duration of the test fires to determine how much of the heat extracted by the fire is delivered into the room, as compared to the heat lost up the flue.

Although a low emissions weight can improve a given stove's Extraction Efficiency score, the total amount of particulate emissions produced by today's EPA approved woodstoves is so small that the affect of particulate emissions on the overall heating efficiency score is negligible. Thus, even a model with an unusually low Emissions rating doesn't necessarily score a high Heating Efficiency rating.

Consider the two models you mention: in Extraction Efficiency testing, the 1.2 gram/hr difference would lighten the total weight of emissions from the cleaner-burning stove by about 10 grams at the end of an 8-hour test burn. Most likely, those 10 grams would be found in the ash remaining in the firebox, eliminating any advantage in Extraction Efficiency. Even if the 10 grams weren't found in the ashes, a difference of 10 grams of particulates from a 40 lb. load of wood would only amount to a .06% advantage in Extraction Efficiency, which would have virtually no affect on the overall Heating Efficiency score.

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Q: I'm shopping for a new EPA approved wood stove, and am intrigued by my neighbor's catalytic model that scored 0.8 grams/hr in the EPA emissions test. This seems far lower than the non-catalytic models you show on our emissions comparison chart. My neighbor admits he has to "blow out" the converter every once in awhile and soak it in vinegar water once a year to keep it working, but this doesn't seem like much of a price to pay for much cleaner burning. Am I missing something, or are catalytic woodstoves just that much better than non-catalytics?

Johnny Burwell,
Exton, PA

Hi Johnny,

Actually, the EPA requires new woodstoves with catalytic converters to test with lower emissions levels than non-catalytic models. This is because the catalyst degrades a bit with every fire, becoming progressively less and less effective at reburning the wood gases until the reburn finally stops altogether, at which point the converter must be replaced. The predicted lifespan of the catalyst varies from manufacturer to manufacturer, but seems to average about 3-5 burning seasons or so. Periodic cleaning with blasts of air or vinegar baths might help improve the performance of an aging catalytic converter by removing flyash deposits which impede the catalytic reaction, but won't restore the converter to its original state: the degradation process continues with every fire. In contrast, non-catalytic burn chambers don't degrade over time, and retain the same emissions level throughout the lifetime of the stove. Any "catalytic stove emissions vs non-catalytic stove emissions" debate should take this into consideration.

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