Older Hotsprings model has the serial number in the filter compartment area.
Depending on what you have it might look like:
DUL-xxxx, I/O-xxxx. X indcating the string of numbers after the letters. Usually it is 4 numbers longs after the letters.
Now the Old School Classic models start with the letter D..Classic model looks like a big dog water bowl fiberglass all around..
Indoor/Outdoor was the start of the new shape of hotsprings model
Serial numbers for the newer Hotspring Spas are located in the equipment compartment. Where all the jet pumps and things are located. (normally the front of the spa)
From 1990 thru 1998 serial numbers should look like this. I'll take the Grandee for example for right now. G-35xxxx. Gstands for Grandee, 3 stands for the 3rd quarted it was made in and 5 is the numer of the year it was made in. In this case it was made in 1995. So you have a Grandee, made in the 3rd quarter of 1995. The X's after the first 2 numbers are numbers to indicate what number it is. not important but nice to have.
Grandee = G
Sovereign = I
Prodigy = H
Jetsetter = J
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