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I don't get the problem with a manufacture listing BHP. Every car ever made is advertised using BHP or Max horse power. Most people understad that a Chevy Corvette does not produce 400hp at 3000rpm's going 55mph down the road.
Try calling some local independant spa repair shops and see what they have to say. Most of the time they are happy to share experience with you when servicing different brands of tubs. You can get an idea of how tubs fare down the road and possible how often they see failures.
Extremely poor analogy. A spa running on high speed produces the continuas HP and not the BHP. A Vette full out (on high speed if you will) is producing maximum HP and torque when floored.Steve