How many hot tubs in the US?

The first hot tub was developed in 1948 by Candido Jacuzzi to provide hydrotherapy or whirlpool treatments in a home. It was marketed in 1955. In 1968 jets were added into the sides of the tub and it became a symbol of luxury. Heating was added in the early 1970s. The Jacuzzi assembly plant produces up to 300 hot tubs per day for domestic and export use. How many are in use just in USA - homes, spas, healthcare facilities - the number would be staggering.

Good info but still didn't answer the question.