什么是afue？
afue stands for annual fuel utilization efficiency. afue (represented as a percentage) indicates how efficient your furnace is. a higher afue rating means greater energy efficiency. if you have an afue of 82%, it means that 82% of the fuel energy put into the system is used to heat your home, while the remaining percent is lost somewhere in the heating process. all furnaces have some loss. this loss is specific to the furnace, and doesn't account for heat loss in ductwork, vents, etc. a typical furnace will have a rating in the mid 80s and a high-efficiency furnace should be 90% or more.
typically 2-3 times per year, depending on how often you use your heating and cooling system, how dusty your home is, and if you have pets or not. a good rule of thumb is to change 1-2 inch filters every three months, 4 inch filters every six months and 5 inch filters every 12 months. if the filter is visibly dirty it's a good idea to change it. the more dense the dirt, the less efficient the system will be.