A British Thermal Unit room-size chart gives the air conditioning capacity that is needed to cool rooms with specific sizes. It allows individuals to select the most energy efficient unit for each room.
Air conditioning units add cooled air to a room while drawing out humidity. Units that are too small do not efficiently cool a room. Units that are too large for a room cool too quickly to allow humidity to be efficiently removed. Both cases require extra energy usage to make a room feel comfortable.
Before using the chart, homeowners need to calculate the square footage of the room. For rooms that are square or rectangular in shape, the square footage is equal to the room's length multiplied by the width. For rooms that are triangular in shape, the square footage is equal to the room's length multiplied by the width, and divided by two. Homeowners can calculate the square footage of odd-shaped rooms by splitting the space into squares and triangles. Finally, homeowners use the calculated area to find the appropriate air conditioning capacity needed.
The BTU room-size chart gives the air conditioning capacities needed for rooms sizes as large as 2,500 square feet, requiring a capacity of 34,000 BTUs per hour.