Now i found info on a unit ID chart now it saying the 6 digit in is you 80%-90% now mine is a number 7 but this was made in 1990 so i don't know if that would be right.I'm trying to find out if it is a 80% or 90% model is NUGE075BG01 so i take it would be the 8 digit in on the 1990 models
If it has plastic venting pipes and a water drain then it is a 90-92% unit. The 80 % units have a 3-4" metal pipe to a regular chimney. All the NUGs I have seen are mids and most of the da*n things have cracked heat exchangers. I would get it checked properly.