A hot tub is a large manufactured tub or small pool full of heated water and used for soaking, relaxation, massage, or hydrotherapy. In most cases, they have jets for massage purposes. Hot tubs are usually located outdoors, and are often sheltered for protection from the elements, as well as for privacy.
There are two different styles of hot tubs:
- Simple wooden-staved soaking tubs
- Fiberglass-reinforced plastic tubs (usually referred to as "spas")
Hot tubs are usually heated using an electric or natural gas heater, though there are also wood-fired hot tub heaters. Hot tubs are also found at natural hot springs; in this case, the water may be dangerously hot and must be combined with cool water for a safe soaking temperature.
Water sanitization is very important in hot tubs, as many organisms thrive in a warm, wet environment. In addition to the use of a pump and micrometre-range particulate filter, bromine or chlorine are used as a primary sanitizer, and often supplemented with an ozone generator and/or UV sterilization. If ozone and UV are not used, a primary algaecide such as polyquat may be additionally needed, since these microbes are more resistant to chlorine than are most bacteria.
This style of hot tub is constructed with wooden staves and steel bands, very much like a very large barrel. The staves are usually made of redwood, cedar, or teak, with most historic tubs made of redwood. Wooden hot tubs are often quite deep, 36"-48", and are inset within a wooden deck for ease of entry. Inside the tub, wooden bench seating is common, forming a ring around the inner circumference of the tub.
Fiberglass spas, also commonly known as Jacuzzi or Whirlpool tubs (though both are brand names), are formed as one piece with shapes that provide a variety of seating arrangements within the tub. They are almost always shallower than wooden tubs, being less than 32" high so they will fit through a standard US doorway. Although wooden tubs were the most common type of hot tub in the 1970s, fiberglass hot tubs now dominate the market as they are less expensive to manufacture, easier to install, and more energy efficient.
Each integral seat is often equipped with one or more water jets that allows water to be directed at parts of the body. The water flow may be aerated for additional effect, and some or all of the jets may also automatically move or rotate, providing a massage-like effect.
Although Jacuzzi is probably the best known brand name of spas, the company primarily concentrates on making bathroom fixtures. Other spas are manufactured by a wide range of mostly-boutique (small production) vendors.
Effective insulation greatly improves the energy efficiency of a spa. There are several different styles of spa insulation: some manufacturers fill the entire cabinet with foam, while others insulate the underside of the shell, the inside of the cabinet, or both. Not surprisingly, many manufacturers advertise the superiority of their approach to insulation, but few independent side-by-side comparisons are available.
Spas usually have at least two water pumps, with one small circulator pump serving the heating and filtration water loop and the other(s) driving the hydrotherapy jets. Sophisticated computer controls are now common and many tubs now are equipped with extensive lighting, sound systems, and even flat-screen televisions with DVD players.
Construction of a Fiberglass Spas
The spa shell is the exteriour of the tub, and is composed of a surface and an understructure that are bonded together during the manufacturing process. The surface is the source of the color, look and feel of the spa, so it should resist deterioration due to the sun, spa chemicals, or normal wear and tear. Some high-end shells have special coatings to make them more stain resistant or have anti-bacterial ingredients molded into the shell material.
The understructure of the shell is made of fiberglass, and provides the strength needed to support hundreds of gallons of water.
The spa cabinet is the skirting around the hot tub. For many years, spa cabinetry was made of wood, most commonly redwood or cedar, and this is still a popular choice today. Wood cabinets require regular maintenance, though, especially in climates where they are exposed to wind, rain, snow, or the drying effects of hot sunlight. Synthetic materials are becoming very popular because they require little or no maintenance to keep their appearance.
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