In today's spa market, companies are completing on the number of jets. Given a specific piping system that supplies water to the jets, the horsepower power needs to increase in a cubic fashion with flow. For example, if flow needs to be doubled horsepower needs to increase by 8 times. Thus, when many jets are utilized, the jets will be small flow rate jets. Otherwise, the horsepower that the pump(s) would have to deliver would be monstrous. Thus a 60 jet spa coupled with a 2 HP pump will not produce anywhere near as powerful of a massage as the same pump powering 6 large flow jets.
We match our pumps and jets so that a 4 jet hot tub will come with a 1.5 HP pump, a 6 jet tub will utilize a 2 HP pump and an 8 jet tub will utilize a 3 HP pump. We also offer a 14 jet tub, but this tub will be supplied with two 3 HP pumps. Jet companies rate their jets in gallon per minute of flow @ a specific psi of pressure. For example, we use jets that require 13 USGPM and, at that flow, will produce a pressure drop across the orifice of 12psi. Thus, for example If you have 4 jets each requiring 13 gallons per minute then your pump must be capable of delivering 52 gallons per minute and also produce sufficient pressure so that there is still 12 psi left for the jets after the pressure drop losses in the piping and components are factored in. We design our tubs to be simple yet effective. As the flow requirements increase because of the number of jets deployed a point is reached where the plumbing design must also be changed. This can include increasing the pipe and component sizes, adding one or more suction fittings, and changing the filter design. This is done in addition to changing the pump size and the number of pumps.