Physics

What is the British Thermal Unit



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Anyone who has dealt with heating or cooling has heard the term BTU. Not everyone knows that the initials stand for British Thermal Unit. BTU's are the standard by which most heating and cooling appliances are rated. The actual computation for the number of BTU's needed in a given situation is related to the climate where the space is located, how the structure has been insulated, and how it will be used. Understanding what a BTU is should not be too difficult for most people to grasp.

British Thermal Units were devised to give people a way to discover how much heating or cooling is needed for a given space.

In the simplest form, a BTU is the amount of energy expressed in calories that needs to be burned in order to heat one pound of water one degree Fahrenheit. If you are preparing to make pasta on your stove, one pound of water from 65 degrees to the boiling point at 212 degrees will require 147 BTU's to get the job done. The heat for the BTU's can be generated with gas, wood, electricity or any other type of fuel. It will still require the same number of BTU's to heat up the water.

In terms of electricity, a BTU can be thought of in slightly different terms.

Electricity is not generally measured in BTU's. It is usually a function of volts, amps, and watts. Expressed as a watt, a BTU is one third of a watt. This means that if you have one volt of electricity pushing one third of an amp, it will generater one third of a watt or one BTU. If you think about this, a standard 100 watt light bulb produces 300 BTU's of heat per hour of use. No wonder it feels warm or even hot when you are exposed to large wattage bulbs at close range.

You must burn approximately 252 heat calories of fuel to produce one BTU of output.

The number of calories needed to heat or cool a house becomes quite large. Most modest homes require 60,000 to 100,000 BTU's to heat them in the winter or cool them in the summer. While these calories are not quite the same as the food that you eat, they are similar. At these numbers, your home sounds like quite an eater. Even small reductions in the temperature settings or the amount of space being heated or cooled will produce large drops in the number of BTU's needed to maintain the desired room temperatures.

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