A recent posting in a website devoted to pork production highlighted the need to insulate exhaust fan louvers to maintain house temperature.  The publication included a calculation of potential loss of heat applying parameters and calculations developed by the American Society of Heating, Refrigerating and Air Conditioning Engineers.  Producers can anticipate a heat loss corresponding to 1cfm per linear foot of crack.  An imperfectly insulated set of louvers on a 58” shutter with an area of 23 ft² can generate a temperature loss of 1,265 btu/hour.  The posting recommended either installation of fan covers or improving the insulation value and function of shutter vanes.  The calculation provided a formula to calculate saving in fuel or improved feed conversion derived from an investment in upgraded louvers or fan covers.