BTUH is an acronym for British Thermal Units per Hour. A British Thermal Unit (BTU) is the unit of heat required to raise one pound of water by one degree Fahrenheit.
The capacity of heating systems such as gas furnaces utilize BTUs per hour (BTUH) as a benchmark to display capacity. Heat extracted by an air conditioner is measured in BTUs, while cooling and heating capacities are measured in BUTH. For example, 12,000 BTUH equals one ton of cooling.
A lower BTUH range furnace is ideal for a small multifamily home, a single family home, or a single floor in a multi-story home. Larger single family homes and light commercial applications generally utilize higher-capacity furnaces.