Why does the EPA tag on my stove say a different efficiency than the specs published for the stove by the manufacturer?

All jurisdictions in the U.S. and some in Canada require the stove be approved by the Environmental Protection Agency (EPA). The EPA clean air test does not include actual efficiency testing. EPA grants all non-catalytic stoves a default efficiency of 63% and because most catalytic designs are around 10% more efficient, the catalytic stoves are granted 72%. The manufacturer’s published calculated efficiency will usually be much higher — some in the 89% range. Keep in mind there are several methods of calculating efficiency so comparing efficiencies may not provide an accurate picture of the stove’s performance.