Pumps in hot tubs and spas have two functions: They circulate water through the filter and heater and power the jets. Pump size varies from small 1/20 to 1/8 Hp circulation pumps to monster 2.5 or 3 Hp pumps used to power many jets. Hot tubs and spas use high-volume pumps. In a high-volume pump, a large volume of water flows at low pressure. This kind of pump is rated in GPM (gallons per minute). Some people get high volume pumps confused with high pressure pumps which are rated in PSI (pounds per square inch). An example of a high pressure pump would be one used in a self service car wash. The water from the hose comes out with great pressure, but little volume. Before the mid-80s, it was common to have a small circulation pump for filtration and heating, and an additional larger pump for powering the jets. Today most hot tubs and spas use two-speed pumps; the same pump circulates water and powers the jets. A two-speed pump provides low cost continuous circulation for filtration, heating, and freeze prevention in low-speed mode and high power and output in jet mode. On low speed these pumps use as little as 150-170 watts and cost only $5-6 per month.
The bigger the pump, the more power in the massage, right! Wrong. What gives a firm massage then? Large volume jets. The larger the jet nozzle, the higher it's GPM rating. We determine a pump's size by adding the total nozzle area of the jets is expected to power. Because there are so many different sizes of hydrotherapy jets, there is no hard and fast rule concerning pump size. In general, large jets (15-20 GPM) require 1/4 Hp per jet. Some jets are so small you can have a 1 Hp pump drive eight to ten of them. At the other extreme, some small swim spa jets require 1 Hp per jet. Manufacturers often use two or more pumps to power individual groups of jets if the total jet area is extremely large. This practice generally saves money for everybody. We match pumps to the size and number of jets they are expected to run. Once the hydrotherapy system has been designed, increasing horsepower has no benefit on jet action. Bigger pumps only operate more jets, they don't increase pressure! If you need more vigorous hydrotherapy action, use high GPM jets. Expect to pay more for a large number of high GPM jets and the required larger pump.
Although it's difficult for the consumer to tell the difference, there are high and low energy efficient pumps. Unfortunately for the spa industry, pump manufacturers have moved to inexpensive, inefficient pumps. The result is a higher operational cost for consumers. For example, in the late 70s, a 1 Hp model consumed 11 amps. Over the years (because of cost-cutting measures in the motor) the same model pump today consumes 15.5 amps. That's an additional 1/2 kW per hour! Great Northern® uses only energy efficient pumps. For example, our 1 Hp pump draws a maximum of 10.3 amps on high speed and only 170 Watts on low speed.
Our Advice: Don't specify a big pump for your spa just because it's bigger. If you want more vigorous hydrotherapy action, ask for large volume jets and an appropriately sized pump. If you're still in doubt, call us.