I am a homeowner looking to buy a new furnace and air conditioner. I have read many stories on this site from homeowners that stated they did not see any savings. In some cases their bills actually increased. On the other hand I have read information on this site and others that the actual performance of a furnace and air conditioner can be measured and documented.I was wondering if any contractor here or anywhere guarantees that the eqipment that they install will perform and deliver the heating and cooling btu's and efficiency within 10% of the equipment rating plate? If not can I hold back payment until this is accomplished?