2013 Federal Furnace Efficiency Law    On 5/1/2013 the minimum efficiency requirement for furnaces in Minnesota, Illinois and Wisconsin will be 90% AFUE. How does this affect you as a homeowner if you have a 80% AFUE furnace? Any furnace replacement and/or installation after 5/1/2013 will require a 90%+ AFUE furnace. 90%+ furnaces are condensing units, meaning they emit water vapor along with carbon dioxide in the flue gases which will rust the sheet metal piping that 80% furnaces...