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Something we get asked a lot here in Waterford Stanley 'What is nominal and maximum output on solid fuel and wood burning stoves and why are they often different?'
Nominal output is the output at which the certified efficiency was achieved during third party testing. The test work is done in accordance with the International standard EN13240. So with an established fuel bed, the correct air settings, fuel load and flue draught to achieve the nominal output the certified efficiency should be obtained
Maximum output is achieved when the fuel bed is established and the stove is refuelled regularly with the air settings on maximum open. Stoves are generally more efficient when they have a high burn rate such as on maximum output.
Maximum output and nominal output can be the same if the testing to EN13240 was conducted at maximum air opening and with a refuel period of approx 1 hr. In some cases where stoves have been classified for continuous use as opposed to intermittent use the nominal may be much lower than the maximum , this is because for continuous use the stove must achieve a refuel period of > 4 hrs leading to a nominal output far below what could be achieved if the refuel period were 1 hr with a smaller fuel load.