How old is my Goodman furnace and how efficient is it?
Model GUEQ80-4REVS
Serial #910482720

Call a local goodman dealer. I don't have a Preston's guide here at home to look up model years and efficiencies. If it has a draft inducer motor it is 80+%. If it has PVC flue pipes it is 90+%. If it has no inducer motor and a metal flue it is -70%.

The first 2 # of the serial is the year the furnace was made they claim it is only 30 days and the furnace is in opration the first 2 # is how they keep track of the warranty