Definition: BTU (British Thermal Unit)
A BTU is a uniform measurement of heat. In layman’s terms it is 'the amount of energy required to heat 1 pound of water (lb) by 1 degree Fahrenheit (°F)’. It is the standard way of measuring:
·The energy content of a fuel.
·The output of a device that generates heat.
To help put this in perspective, fuels have a different BTU rating which denotes their efficiency and output.
·1 Gallon of Methanol - 77,600 BTUs
·1 Gallon of Propane - 105,600 BTUs
·1 Gallon of Petrol - 150,000 BTUs
·1 Gallon of Diesel - 166,600 BTUs
This principle can also be applied to solid fuels.
Definition: W (Watt)
A Watt is an International System (SI) unit of power which measures the rate of energy conversion. It is the rate of heat transfer from one body to another, and is defined as one joule per second.
Heat flows between 2 substances that in non-equilibrium with each other, this is what makes heating systems work.
Electricity is converted to heat in the heating element – The heating element warms the cooler medium (air/water) which it is in contact with – The air/water then moves away from the heating element by convection (or other means if say water).
Provided there is power coming to the heating element the air will keep heating until equilibrium is reached. This rate of this transfer rate is quantified by the number of Watts.