The capacity of a warm air furnace is usually rated in which units?

The capacity of a warm air furnace is usually rated in which units?

• A. Watts
• B. Horsepower
• C. CFM
• D. BTUs

Answer: (D)

Heat capacity for a warm air furnace is a rate of heat output, not a total energy amount. In residential HVAC, that rate is expressed as BTU per hour (BTU/h), which shows how much heat the furnace can add to the air each hour. This matters because efficiency also plays a role: the stated BTU/h input is converted into usable heat at a certain AFUE, so the actual heat delivered depends on that efficiency. Other numbers like watts or horsepower measure power for electricity or motors, not the heat produced, and CFM measures how much air is moved rather than how much heat is generated. Some contexts use MBH (thousand BTU/h) or convert kW to BTU/h, but BTU/h is the standard unit for furnace heating capacity.

Heat capacity for a warm air furnace is a rate of heat output, not a total energy amount. In residential HVAC, that rate is expressed as BTU per hour (BTU/h), which shows how much heat the furnace can add to the air each hour. This matters because efficiency also plays a role: the stated BTU/h input is converted into usable heat at a certain AFUE, so the actual heat delivered depends on that efficiency. Other numbers like watts or horsepower measure power for electricity or motors, not the heat produced, and CFM measures how much air is moved rather than how much heat is generated. Some contexts use MBH (thousand BTU/h) or convert kW to BTU/h, but BTU/h is the standard unit for furnace heating capacity.