BTU – What do this Acronym mean?

Let’s take a look at Wikipedia:

“The British thermal unit (symbol Btu or sometimes BTU) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to heat one pound of water by one degree Fahrenheit. In scientific contexts the Btu has largely been replaced by the International Standards (SI) unit of energy, the joule (J).

The unit is most often used as a measure of power (as Btu/h) in the power, steam generation, heating and air conditioning industries. It is still used in metric English-speaking countries (such as Canada), and remains the standard unit of classification for air conditioning units manufactured and sold in many non-English-speaking metric countries. “

To get a better feel for energy in BTU which can be converted into the energy unit joules (J) we need to see what a joule is. A joule is Watt second (Ws), an energy unit used in measuring electric energy (1kWh = 3,600×1000 Ws). Therefore 1 BTU or 1055 Joules is 1.005 KW Second or about 0.0003 KWh

But when your heating and air technician talks about equipment, he is using the term ton, like a 3 ton AC unit. He actually means a “ton of cooling” to describe the capacity or power of an air conditioning unit.  A “ton of cooling” is the equivalent of 12,000 BTU/h and this is needed to freeze a ton of ice in 24h. A ton is approximately 3.35 kW.

Summary:

• A BTU or Btu or British thermal unit is a unit of energy and is the equivalent of about 1,055 J or 1,055 Ws.
  A BTU is defined to increase a pound of water by 1degree Fahrenheit.
• The power or capacity of cooling / refrigeration equipment is measure in tons (tons of cooling) and equals approximately 3.35kW
  A one ton unit is needed to freeze a ton of water in 24h.

So when your heating and air company proposes a 3 ton AC unit for your house, they are proposing an AC unit that provides about 10kW of cooling.  Multiply this with rate from your power company for electricity times the efficiency ratio* of your AC unit times the hours of run time, you start to understand why cooling and air conditioning can be quite expensive.

* Efficiency ratio will be discussed in our next block.