A hot tub is a large tub full of water used for hydrotherapy, relaxation or pleasure. Some have powerful jets for massage purposes. Hot tubs are sometimes also known as "spas" or by the trade name Jacuzzi.
In contrast to a typical bathtub, a hot tub is designed to be used by more than one person at a time, with many models accommodating four or more people. Hot tubs are usually located outdoors, although they can be installed indoors. Another difference between baths and hot tubs is that soaps and shampoos are not used in wet-jetted hot tubs.
The earliest hot tubs were calderas in which hot stones were placed to heat the water. Therma in Ikaria has been a very popular place particularly for hydrotherapy ever since the 4th century BC. The remains of wrecked marble bathtubs along with a pre-historic aqueduct that have been unearthed from this area bear ample testimony of the place's popularity in the ancient times.
In ancient Rome there were three types of baths: baths at home, private baths, and public baths. The practice of bathing was so engrained that the Roman legions, during their long occupations in foreign lands, built their own baths at mineral and thermal springs in the newly conquered lands. Examples are found all over Europe.
In the 1940s hot tubs began to appear in the US, inspired by the Japanese ofuro. Hydrotherapy pumps were introduced by Jacuzzi. Fiberglass shell hot tubs appeared around 1970 and were soon superseded by cast acrylic shells.
The plumbing of the hot tub consists of:
- A pressure system delivering water to the jets
- A suction system returning water to the pumps.
- A filtration system: the plumbing has to incorporate a filter system to help clean the water. Some models use a separate small 24/7 filter pump while others use programmed settings of the main pumps.
- Induced air: The jets may use a venturi effect to incorporate air into the water stream for a lighter massage effect; this requires another set of hoses.
- Some models use an air blower to force air through a separate set of jets for a different "bubbly" massage effect; this is a separate system from the induced air.
- An ozone system: ozonation is a common adjunct to water maintenance, and if installed will have its own set of hoses and fittings.
Heating & Energy Use
Hot tubs are usually heated using an electric or natural gas heater, though there are also submersible wood fire hot tub heaters, as well as solar hot water systems. 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. Effective insulation greatly improves the energy efficiency of a hot tub.
There are several different styles of hot tub insulation: some manufacturers fill the entire cabinet with foam, while others insulate the underside of the shell, the inside of the cabinet, or both. Many manufacturers advertise the superiority of their approach to insulation, but few independent side-by-side comparisons are available. The hot tub pump and hot tub heater represent most of the power consumption in a hot tub and vary in use of power depending on their size.
Sanitation & Water Quality
Sitting in water above normal body temperatures can cause drowsiness which may lead to unconsciousness and subsequently result in drowning. The U.S. Consumer Product Safety Commission (CPSC) recommends that water temperatures never exceed 40 degrees Celsius. A temperature of 37 degrees is considered safe for a healthy adult. Soaking in water above 39 degrees Celsius can cause fetal damage during the first three months of pregnancy.
It is also recommended to install residual-current devices for protection against electrocution. The greater danger associated with electrical shock in the water is that the person may be rendered immobile and unable to rescue themselves or to call for help and then drown.
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