Without the Model number of the old one, nobody can tell you. the year 2000 was just about the time that Dometic and RVP started producing 15k AC units. before that the largest was 13.5k. The odds are, on a Fleetwood Bounder your year model the original WAS a 13.5k unit. Since they delt with a ESC to replace your unit, their paperwork should indicate the OLD model number. IF you have an Energy management system(EMS), then you probably had a 13.5k. When 15k came out the 15k was an OPTION and not standard. So, you need to contac Fleetwood and give your VIN and ask what size was on your particular unit. Doug