Monday, September 06, 2010 4:22 PM
Electrically; 1 watt = 3.412 BTU/H.
Therefore a 500 watt electric heater will generate 500(w) x 3.412(btu/h) = 1706 BTU per hour.
Note: To determine the necessary requirements for a specific room or area, you must have a 'load calculation' performed. This will take into account the design indoor temperature, internal heat generating sources (including bodies), insulation factors of the exterior enclosure and outdoor conditions. This can be accomplished with some online tools to arrive at a resonable approximation, or contact your favorite HVAC contractor.
For a thorough conversion chart of most energy sources to their respective heating btu's see this page...
http://www.energystar.gov/ia/business/tools_resources/target_finder/help/Energy_Units_Conversion_Table.htm
Hope that helps.
ThomE