Residential A/C Calculations

Air conditioners come in many sizes.

Sizing an air conditioner correctly for a room in a house or for central air conditioning systems is essential for efficient cooling. The units carry different size ratings, depending on how they function.

Size

Improperly sized air conditioners cost more money to operate, especially if the units are too big for the space. Latent heat is a term used for the amount of humidity in the air. Humidity carries a lot of heat and air conditioners which are too big do not effectively remove the humidity because they do not run long enough to condense the water in the air. Conversely, smaller air conditioners cannot keep up with the sensible heat (outdoor heat), or heat from cooking and body temperatures.

Considerations

Professional heating, ventilation and air conditioning (HVAC) companies use a complex program called Manual J, a piece of software that includes data input about the size of the home, typical humidity, heat gain, insulation levels and exposure to sunshine to determine the size of the unit. Portable and window air conditioners carry labels on the box indicating the British Thermal Units (BTUs) and the maximum size room or space they can cool.

Types

Manufacturers of room and portable air conditioners refer to their size in BTUs. Manufacturers label the size of heat pumps by kilowatts and central air conditioners by tons. Each of the measurements can be converted to BTUs, kilowatts and tons. There are 12,000 BTUs in one ton of air conditioning and 3,413 BTUs in one kilowatt. A BTU is capable of raising one pound of water one degree.

References

• Air Conditioner Selection: Discover Ways for Air Conditioner Sizing
• Energy Star: Sizing Heating and Cooling Systems