Heater Glossary

Air changes/hour - The number of times per hour that the air in a room or building is changed by mechanical means.

BTU - The basic unit for measuring the output of a heater (acronym for British thermal unit). One BTU equals the amount of heat required to raise the temperature of one pound of water by one degree F.

Combustion - The chemical action of a substance with oxygen resulting in the evolution of heat and some light. The three requirements for combustion are sufficiently high temperatures, oxygen, and fuel.

Conduction - The transmission of heat through and by matter.

Convection - The transmission of heat by the circulation of air.

Heat exchanger - A device used to transfer heat from one medium to another. It allows fumes and the products of combustion to be vented away from the heated airflow in an indirect-fired heater.

Heat rise - The desired rise in temperature in degrees F for a heated area. To determine heat rise, subtract the outside temperature from the desired inside temperature in the area being heated.

Resistance heating - Heat generated by electric current passing through a resistance
wire. This is the most common type of electric portable heater.

Static pressure - The pressure which tends to burst a pipe. It is used to overcome the frictional resistance to flow through the pipe. In the case of forced-air heating systems, static pressure forces air through ducting and enclosed areas. It is usually expressed in inches of water column.

Therm - A unit of heat equal to 100,000 BTU's. It's also used to measure natural gas and as a basis for comparing different fuel types. One therm = 40 cu. ft. of natural gas.

Thermostat - A device that automatically responds to temperature changes and activates switches controlling heaters and other HVAC equipment.

How many BTU's of heating capacity do you need?

The formula below can serve as a rough guide for determining the heat requirements for common building applications:

BTU Required = Square footage x Ceiling Height x ?t x Building Factor
Where  = Temperature Rise (Desired Temp. F inside ?Outside Temp F)
Building Factors : .135 (Sealed building), .145 (Unsealed building), .160 (Tent)

Example: A 4000 sq. ft. unsealed building has an 8' ceiling height. The desired temperature is 70?F and the outside temperature is 30?F. Therefore, the desired temperature rise (???? t) is 40?

BTU Required = 4000 x 8 x 40 x .145 = 185,600

Other factors to consider are insulation, ventilation, and the number of rooms being heated. After determining the most suitable type of heater and the BTU requirements for your application, select a heater (or heaters) with a BTU rating equal to (or greater than) your requirements.

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