A BTU or British thermal unit is a measure of heat. One BTU is equal to the amount of thermal energy that is required to heat one pound of water one degree Fahrenheit. Any device that raises or lowers heat will have a BTU rating. Examples include range elements, water heaters, furnaces and air conditioners.
HVAC professionals use these units in order to measure the heating capacity of a furnace and the cooling capacity of an air conditioning system or unit. The higher the BTU measurement means the more powerful the unit and higher the price of the system.
A HVAC professional can help you determine the proper BTU for your home. Things such as whether the room is shaded or not, if it is a kitchen, has high ceiling or you live in a warmer climate all impact the number of BTUs needed. A room that is using too large of a BTU size will cycle off too fast and the unit itself will not remove humidity from the air. If you have both heat and air the units must be roughly matched or they will not work together properly. As an example, a 40,000 BTU furnace fan will, in most cases, not provide adequate airflow over a 5 Ton (60,000 BTU) AC evaporator coil.
Knowing the proper BTUs for your home will be more energy efficient, which will help you save money in the long term and make your home more environmentally friendly.