Heating BTU vs. Room Size

Heating BTU

• BTU is the acronym for British Thermal Unit. Technically, BTU measures how much heat is required to raise the temperature of one pound of water through one degree Fahrenheit. The BTU capacity is used to determine the right size furnace required to heat a home. For example, a furnace may be labeled as having a 100,000 BTU capacity and an efficiency rating of 80 percent. This would mean that the furnace is capable of producing 80,000 BTUs of heat, given that 20 percent of its energy output does not convert to useable energy for heating.

Room Size

• Room size is a key consideration in determining heating requirements. Rooms are measured in terms of square footage, which measures the width and length of floor space (width multiplied by length) of the room, and cubic footage, or volume, which takes into account the ceiling height of the room (square footage multiplied by ceiling height). Volume is an important factor in determining the total amount of space required to heat the room, from floor to ceiling. For example, a room that is 8 feet wide and 10 feet long is 80 square feet, and if the room has 8-foot tall ceilings, it measures 640 cubic feet.

Differences

• A BTU is a heat measurement and room size is a space measurement. BTU input and output can vary in terms of how much heat it actually delivers, based on factors such as the size of the furnace, how many windows the home has, how much sunlight and solar heat it absorbs and insulation standards. However, room size measures are constant and fixed.

Comparatives

• The size of rooms and the overall cubic footage determine the necessary BTU capacity for the heating appliance. In the case of a central heating system, this would mean calculating the heating requirements for every room in the home, to determine the correct BTU capacity for the furnace. If just a room or space needed heating, the BTU capacity would be based on what is required for that room, zone, or space. For example, an HVAC (heating ventilation air conditioning) technician might conclude that a home with eight rooms, covering 2,000 square feet would need a furnace with an 80,000 BTU capacity. In another case, a technician might calculate that a downstairs area that's 1,000 square feet and has an open floor plan, combining living room, dining room and kitchen, might require a furnace with a 60,000 BTU capacity. In the latter example, even though the room size is one-half the earlier example, the technician would determine a need for more BTUs, because the room has floor-to-ceiling windows and does not receive a lot of sunlight. This demonstrates the many variables involved in determining the BTU heating requirements for various room sizes and configurations.