The Btu or British Thermal Unit is one of the basic measure of heat energy. One Btu is the amount of energy it takes to raise the temperature of one pound of water from 39 degrees to 40 degrees Fahrenheit. There are several different measures of the Btu that vary depending on the starting temperature of the water and the calculation method. To convert Btu into International System of Units
. measures for energy, the conversion formula is one Btu = 1055.056 joules; for other conversions, see the SiMetric conversion table: http://www.simetric.co.uk/sibtu.htm.Btu measures are most commonly used in the context of heating and air conditioning industries, as well as in power and steam generation, even in countries that otherwise use metric standards.Air conditioners, in particular, work best when their cooling power capacity is appropriate to the size of the room they're cooling "" air conditioners that are not powerful enough will not cool the room completely, whereas air conditioners that are too powerful cool the room but don't remove enough of the humidity. Therefore, contractors and builders will calculate the correct Btu ratio per square foot of the room to be cooled. Although some people use the 20-50 Btu per square foot rule of thumb as a general indication of the appropriate size for an air conditioner and use 20 Btu per square foot rule of thumb as a general indication for an heating system, or calculate heating system Btus on the 1 Btu per 55 cubic feet of air rule, there are actually several complicating factors, including the typical outside temperature, the quality of the insulation, the speed the room will need to be heated and the location of the heater.Fortunately, for heating systems, there are multiple online calculators that use some of those complicating factors to calculate the heating needs more accurately, including the Heater Shop Btu calculator (http://www.heatershop.com/btu_calculator.htm) and the Herman Nelson Btu calculator (http://www.herman-nelson.com/btu_calculator.cfm). Home Depot runs a similar air conditioning calculator (http://www.homedepot.com/webapp/wcs/stores/servlet/THDCalcRoomACView?metric=false&catalogId=10053&storeId=10051&langId=-1). More reference links: http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized http://www.acdirect.com/systemsize.php
