Air conditioners, to a normal consumer, often appear simply as metal boxes with vents on the front and back. There is little way to visually identify the power of the unit. Simple wattage is not always an accurate indicator, and with ever improving technological advancements, can actually be misleading at times.
For this reason, air conditioners have their cooling power measured in units called BTUs. A BTU, or British thermal unit, is a scientific measurement of how much energy is required to cool a single pound of water by one degree Fahrenheit.
When looking at an air conditioner, there is often a BTU measurement listed with other information. This is really a measurement of BTUs per hour, or the total amount of cooling energy expended per hour. The higher the number of BTUs, the stronger the cooling power of the air conditioner.
The importance of an air conditioner’s BTU rating comes into play when considering energy efficiency and comfort. While it may seem like a good idea to purchase the air conditioner with the highest possible BTU rating, it may actually cause the unit to not function as intended.
In order for an air conditioner, regardless of BTU, to function correctly it needs to not only cool the air in a room, but also to dehumidify it. Choosing an air conditioner with the correct amount of BTUs will ensure that the room is cooled and dehumidified at the correct rate.
If the air conditioner’s BTU rating is too high for the room it may waste energy cooling it beyond the needed point before it has a chance to shut off. Alternately, if it cools the room too quickly and then shuts off, the room itself will be very humid and uncomfortable.
There are general guidelines for an air conditioner’s BTU rating in relation to the size of the room that it is cooling. For a room of approximately 400 square feet (20’ x 20’), you would want an air conditioner with around 8000 BTU. For a room of 800 square feet, you would want an air conditioner with about 14,000 BTU. Finally, for large rooms of 1000 square feet or more you would want an air conditioner rated at 20,000 BTU or more.
For areas that are larger than 1200 square feet, other cooling options, such as central air, should be considered since a systematic heating and cooling system would be more energy efficient.
You will want to look at increasing the suggested BTU rating for the air conditioner depending on certain conditions within the room. Specifically, consider the number of windows in the room or whether it is adjacent to an un-insulated roof or exterior wall. Increase the BTU rating also if the room is adjacent to, or is, a kitchen. Less important factors include the number of people who will be sleeping in the room if more than one, and whether the room is in contact with a room containing a heat-producing appliance like a water heater or boiler.
As efficient as air conditioner technology is today, there are still actions which must be taken when purchasing and installing the units. Make sure the window that the air conditioner is placed in is insulated, make sure the air conditioner’s BTU rating is appropriate for the room, and make sure that you have the unit’s thermostat set to a comfortable level. Using the energy saving mode available on most models will also help to reduce cooling costs.
Finally, if you are in an area with harsh winters, try and remove the air conditioner for the cold seasons. It will help to extend the life of the unit and help to keep heat in your home throughout the winter.