According to the standards of the ASME (American Society of Mechanical Engineers), Boilers can be classified on the basis of pressure into the following types.
Low Pressure Boilers
Boilers with operating steam pressure not exceeding 1.021 atmosphere and a temperature of 394 K.
Power Boilers
Power Boilers are those boilers whose pressure rating and temperature are above those of Low pressure boilers.
Miniature Boilers
These are boilers with very small capacity with a pressure less than 6.8 atmospheres and a gross volume less than 0.1415 cubic metres.