What is a BTU and what does it mean?
A BTU is a British Thermal Unit that is used to measure the amount of heat omitted by a source, in this case the source is the fireplace. In technical terms, a BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. Note: An average 2,000 square foot house with ceilings around 9-10ft high requires around 100,000 BTUs to keep warm. Supposing that house was divided into four rooms, one could estimate needing around 25,000 BTUs to heat that space. An average 36″ firebox puts out about 25,000 BTUs, which will comfortably heat an average sized room. For a space that has more square footage and higher ceilings, one would consider investing in a larger firebox. Likewise, for a space with less square footage and lower ceilings, one would invest in a smaller firebox.