A British Thermal Unit (Btu) is a measurement of heat energy. One Btu is the amount of heat required to raise one pound of water by one degree Fahrenheit. Btus per hour (Btuh) is the benchmark used to estimate the capacity of heating systems, such as gas furnaces.
Lennox® furnaces are available in heating capacities ranging from 30,000 to 135,000 Btuh.
A furnace with a lower Btuh range is typically made for small multifamily home, single family home, or a single floor in a 2-story home.
Higher-capacity furnaces are made for larger single family homes, large single story homes, and light commercial applications.
