Hot tub - AbsoluteAstronomy.com

A hot tub is a large tub or small pool full of heated water and used for soaking, relaxation

Recreation

Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure and are considered to be "fun"...

, massage

Massage

Massage is the manipulation of superficial and deeper layers of muscle and connective tissue to enhance function, aid in the healing process, and promote relaxation and well-being. The word comes from the French massage "friction of kneading", or from Arabic massa meaning "to touch, feel or handle"...

, or hydrotherapy

Hydrotherapy

Hydrotherapy, formerly called hydropathy, involves the use of water for pain-relief and treating illness. The term hydrotherapy itself is synonymous with the term water cure as it was originally marketed by practitioners and promoters in the 19th century...

. 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. Other variants in naming include "Spa", and the trade name "Jacuzzi

Jacuzzi

Jacuzzi is a company that produces whirlpool bathtubs and spas. Its first product was a bath with massaging jets. The term "jacuzzi" is now often used generically to refer to any bathtub with massaging jets.-History:...

". These variants can be used to mean an indoor fixture, but a "Hot Tub" is almost always outdoors.

There are essentially two different styles of hot tubs:

Simple wooden-staved soaking tubs
One piece plastic tubs (usually referred to as spas
Spa (disambiguation)
A spa is a therapeutic water treatment, named after Spa, a municipality in BelgiumRelated terms:* A mineral spa* A destination spa or day spa* A hot tubSpa can also refer to:* A convenience store in parts of Massachusetts...

)

Hot tubs are usually heated using an electric or natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

heater, though there are also submersible wood-fired heaters, as well as solar hot water

Solar hot water

Solar water heating or solar hot water systems comprise several innovations and many mature renewable energy technologies that have been well established for many years...

systems. Hot tubs are also found at natural hot spring

Hot spring

A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...

s; in this case, the water may be dangerously hot and must be combined with cool water for a safe soaking temperature.

Water sanitization

Disinfection

Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...

is very important in hot tubs, as many organisms thrive in a warm, wet environment. Maintaining the hot tub water chemistry is also necessary for proper sanitization and to prevent damage to the hot tub. In colder climates, if the hot tub is not used year-round, it should be "winterized" for the off season.

Wooden tubs

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 older tubs made of redwood. Wooden hot tubs are often quite deep (90–120 cm, 36"-48"), and can be 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.

One piece hot tubs

One piece spas, also known as unibody spas, are formed as one piece with shapes that provide a variety of seating arrangements within the tub. 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

Massage

effect.
Although wooden tubs were the most common type of hot tub in the 1970s, one-piece hot tubs now dominate the market as they are less expensive to manufacture, easier to install, and more energy efficient. In America, these kinds of tubs are also incorrectly referred to as Jacuzzi
Jacuzzi
Jacuzzi is a company that produces whirlpool bathtubs and spas. Its first product was a bath with massaging jets. The term "jacuzzi" is now often used generically to refer to any bathtub with massaging jets.-History:...

or Whirlpool tubs, though both are brand names.

One piece spas are usually shallower than wooden tubs, usually being 80–95 cm (32" to 36") in height to fit through doors and narrow hallways. Cranes are occasionally used to place one piece spas in a backyard or other location that does not have adequate clearance for carrying the tub.

Spas usually have between one and four water pumps, with one circulation pump serving the heating and filtration water loop and the other(s) driving the hydrotherapy jets. Sophisticated computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

controls are now common and many tubs now are equipped with extensive lighting

Lighting

Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...

, sound system

Sound reinforcement system

A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience...

s, and even flat panel television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

s with DVD

DVD

A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

players, or hydraulophones (water-based musical instruments built into the hot tubs).

Construction of a one-piece spa

The spa shell is the exterior 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.

There are two primary methods used for manufacturing one piece spa shells:

vacuum forming
Vacuum forming
Vacuum forming, commonly known as vacuuforming, is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto or into a single-surface mold , and held against the mold by applying vacuum between the mold surface and the sheet.The vacuum...

of an acrylic base by placing the sheet over a mold and heating with an overhead heater while pulling a vacuum on the mold
rotational molding
Rotational molding
Rotational molding, also known as rotomolding, rotocasting or spin casting, is a molding process for creating many kinds of mostly hollow items, typically of plastic....

: involves placing polyethylene powder in an aluminum mold which is then heated and spun in a large oven so that the plastic melts and takes the form of the mold.

The understructure of the shell provides the strength needed to support hundreds of gallons of water and the weight of the bathers (the cabinet is not normally part of the weight-bearing structure). The substructure is generally made of FRP (commonly called fiberglass

Fiberglass

Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...

), though some companies use ABS

Acrylonitrile butadiene styrene

Acrylonitrile butadiene styrene is a common thermoplastic. Its melting point is approximately 105 °C ....

or other plastics. Some manufacturers build a self-supporting shell, while others use secondary supports of wood or metal under the seats or in high-stress areas to reduce the amount of FRP required. Some companies use a perimeter frame of wood or metal to support the rim.

The plumbing of the spa consists of several distinct systems:

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
Venturi effect
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi , an Italian physicist.-Background:...

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
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

system: ozonation is a common adjunct to water maintenance, and if installed will have its own set of hoses and fittings.

The spa cabinet is the skirting around the hot tub, and serves as both an enclosure for the plumbing and a decorative wrap. For many years, spa cabinetry was made of wood, most commonly redwood or cedar, and this is still a popular choice. Wood cabinets require regular maintenance, though, especially in climates where they are exposed to severe weathering. Synthetic materials are increasingly popular because they are seen as requiring relatively little maintenance to keep their appearance.

Safety

As with use of a swimming pool, lake or other body of water, safety is important when using a hot tub. Spas are equipped with drains and pumps that can create a powerful suction. It is possible for hair to become tangled in the drain — keeping your head under water. Young children should never be left unattended near or in a hot tub. As well, women who are pregnant, or are trying to get pregnant, should not use hot tubs.

Energy efficiency

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. The spa 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.

Energy efficiency of the tubs has been studied by the Pacific Gas and Electric Company

Pacific Gas and Electric Company

The Pacific Gas and Electric Company , commonly known as PG&E, is the utility that provides natural gas and electricity to most of the northern two-thirds of California, from Bakersfield almost to the Oregon border...

. The industry has responded to the study.

After this study, both the California Energy Commission and National Resources Canada have taken an interest in the energy efficiency of portable spas (late 2006).

California's portable electric spa listing include R Values of thermal insulation

Thermal insulation

Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

, and standby watt

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

s.

Spa covers have been shown to reduce most if not all of the evaporative losses from the pool when not in use. With this component of heat loss being 70% a cover with even a small R-value

R-value (insulation)

The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...

is able to achieve as much as a 75% reduction in heating costs when used as opposed to leaving the water surface exposed.

There are several different types of spa covers. Some covers are better for insulation and therefore are lighter on internal parts and energy efficiency. Some examples of covers are: insulated, aluminum, rolling, or a tonneau.

Sanitation and chemistry

Maintaining hot tub water sanitation and chemistry is necessary to prevent the spread of disease as well as damage to the tub. In addition to the use of a pump and micrometre-range particulate filter, bromine

Bromine

Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

, chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

or mineral sanitizer

Mineral sanitizer

Mineral sanitizers for the swimming pool and spa use minerals, metals, or elements derived from the natural environment to produce water quality benefits that would otherwise be produced by harsh or synthetic chemicals....

s are almost always used as a primary sanitizer, and often supplemented with an ozone

Ozone

Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

generator, UV sterilization, and/or silver and copper ion generator (also known as a "spa ionizer").

To periodically remove any stubborn microorganisms, or in the event of poor water sanitation, "shocking" the hot tub is recommended. This can be done with either potassium monopersulfate (usually referred to as "non-chlorine shock"), or a relatively large dose of granulated chlorine. The hot tub should not be used for a period of time after starting the shock treatment, typically 15 minutes for potassium monopersulfate and 8 hours for chlorine.

Maintaining the water chemistry involves keeping the pH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

, total alkalinity, and calcium hardness within acceptable margins. If the pH

is not maintained in the correct range, chlorine

Chlorine

will not be effective at eliminating bacteria. Also, severe problems with the water chemistry may cause metal parts of the tub's plumbing to corrode

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

, damaging or destroying them. The Langlier Saturation Index is important to determine and maintain properly, so that calcium and magnesium deposits do not form in the water heater

Poor hot tub sanitation, whether by improper design or failure of the sanitation system, can result in disease transmission and litigation. It is recommended to have multiple sanitation systems to prevent system failure if one sanitation subsystem fails.

Health issues

Bacterial infections, including respiratory infections, may arise if the hot tub is not properly disinfected. Because a hot tub is constantly kept warm, bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

can thrive. Water droplets are inhaled by bathers, along with any pathogens, which can infect the lungs and respiratory passages.

Commonly used terms

Hot tub: name originally given to the earliest tubs that were round, made of wood, and located outdoors; now is commonly used interchangeably with the phrases 'home spa' and 'portable spa'.

Home spa: generally made with a plastic shell; surrounding cabinet may be made of wood or synthetic materials; can be used to describe an above ground, in-ground, indoor or outdoor spa.

Portable hot tub/portable home spa: name for any hot tub/home spa that is pre-assembled and sits above ground; actual size and features of a portable hot tub vary widely, from small portable hot tubs that weigh only a few hundred pounds and plug into a household outlet to large tubs that weigh several thousand pounds and require specific installation methods and electrical wiring.