Why Hot Tub Temperatures Max Out at 104 Degrees

Many people question why their spa will only heat to 104 ºF. Throughout history public bathing was done at higher temperatures. Even today, in Japan, many public bath houses have water up to 115 ºF.

Hot tubs & spas in the United States, Canada and most parts of the world have been regulated to obtain a maximum temperature of 104 ºF since 1980.  On Dec 31, 1979, the Consumer Products Safety Commission, CSPC, released advisory #79-071.

The advisory warned that heat strokes could be caused by water temperatures of 106 °F or higher.  The CSPC recommended a maximum temperature of 104°F for both public and private hot tubs and spas.

The advisory was adopted by Underwriters Laboratory (UL) and lists it in their controlling document (#UL 1563) for home spas, equipment assemblies and associated equipment. The relevant portion of this document as it pertains to max temp regulations for home tubs and spas is section 32; Temperature Regulating Controls…

32.1 – A unit shall be provided with a water temperature regulating control that has a maximum set point of 40 °C (104 °F) in the tub.

32.2 – The temperature regulating control shall be adjustable and shall have marked settings, but it shall not have any settings marked hotter than 40 °C (104 °F).

32.3 –  A digital temperature regulating control that displays the selected temperature, but no higher than 40 °C (104 °F), may additionally display the actual temperature of the water.

UL has strongly advised that any hot tub or spa manufacturer that produces a control, or modifies a standard control, to exceed 104 °F is in violation of their UL listing and can have their listing pulled by UL.

The actual 1980 CSPC cover letter that accompanied advisory #79-071 is listed below:

U.S. Consumer Product Safety Commission Warns of Hot Tub Temperatures
Release # 79-071
December 31, 1979

WASHINGTON, D.C. (December 31, 1979) — Safety officials frequently warn the public about the dangers of drinking and driving. Now the U.S. Consumer Product Safety Commission is cautioning that drinking and hot tubing do not mix well either.

According to CPSC staffers, the use of hot tubs at water temperatures above the normal body temperatures can cause drowsiness which may lead to unconsciousness and subsequently result in drowning.

The risk of drowning is significantly heightened if individuals consume alcoholic beverages while, or prior to, soaking in hot water, CPSC staff warns. The Commission has been informed of 10 deaths recorded so far in 1979, three of which involved alcohol-related drowning in hot tubs heated to approximately 110 degrees Fahrenheit.

Even if no alcohol is consumed, extremely hot water during hot tub use can threaten life, CPSC reports. Soaking in a hot tub with water heated to 106 degrees Fahrenheit, for example, can raise human body temperature to the point of heat stroke (or impairment of the body’s ability to regulate its internal temperature). These conditions can be fatal even to fully healthy adults.

Hot tub sales in the U.S. have increased about 125 percent in the past two years, from approximately 40,000 tubs sold in 1977 to approximately 90,000 sold this year. Based on industry projections, CPSC estimates that sales could climb as high as 135,000 tubs next year, a 50 per cent increase over 1979 sales.

As hot tubs have gained in popularity throughout the nation, so have concerns at CPSC that consumers learn how to use these products safely. Accordingly, CPSC staff strongly urges consumers to observe the following safety rules for hot tub use.

Safety Rules For Hot Tubs

  • Hot tub water temperatures should never exceed 104 degrees Fahrenheit. A temperature of 100 degrees is considered safe for a healthy adult. Special caution is suggested for young children.
  • Excessive drinking during hot tub use can cause drowsiness which could lead to unconsciousness and subsequently result in drowning.
  • Pregnant women beware! Soaking in water above 102 degrees Fahrenheit can cause fetal damage during the first three months of pregnancy (resulting in the birth of a brain damaged or deformed child). Pregnant women should stick to the 100-degree maximum rule.
  • Before entering the hot tub, users should check the water temperature with an accurate thermometer; hot tub thermostats may err in in regulating water temperatures by as much as four degrees.
  • Persons with medical history of heart disease, circulatory problems, and diabetes or blood pressure problems should obtain their physician’s advice before using hot tubs.
  • Persons taking medications which induce drowsiness, such as tranquilizers, anti-histamines or anti-coagulants, should not use hot tubs.

CPSC staff currently is working with staff from the Spa and Tub Association ( a division of the National Swimming Pool Institute) and the International Spa and Tub Institute (both of Santa Ana, California) as they develop voluntary safety standards for the manufacture, installation, and use of hot tubs. These standards, which are expected to reflect many of the above safety warnings, may take effect as soon as spring, 1980.

 

 

Hot Tub Location Guidelines

Hot Tub Location Guidelines

The most important part of any hot tub installation is proper planning and the first two steps of the planning process are deciding the ideal location for your hot tub and your hot tub equipment.

The vast majority of our customers prefer to install their hot tubs outdoors, but our tubs can be installed just as easily inside your home as out.

Our Hot Tub Photo Gallery is full of unique location ideas, creative inspiration and great examples of where other hot tub owners have located their hot tubs.

Location of Your Hot Tub

Roberts Hot Tubs has been in business for over 42 years and history has taught us that your tub will be used and enjoyed more often the closer it is to your house or bedroom.

Installing your hot tub on or submerged in an existing outdoor deck is ideal for many hot tub owners, but please be aware that most decks are not designed to support the weight of a hot tub filled with water.

We strongly advise that all hot tub owners considering tub installations on existing decking check with a licensed engineer prior to beginning tub installation. Please remember that the average hot tub filled with water weighs approximately 5000 lbs. before you and your friends jump in!

Outdoor Installation Locations

Depending on where you live and the size of your yard, there can be an endless number of ways and places to install an outdoor tub.

That said, there are certain health and safety restrictions that will influence where your tub can be located.

  1. For stability and settling purposes, the tub itself must sit on a single solid concrete surface. Everything settles over time and just like the concrete slab under most homes, concrete settles but remains flat. Please do not set your tub or equipment on gravel.
  2. The tub rests on chine joists (sleepers) that we provide rather than making direct contact with the concrete pad. The size of the concrete pad can be 6 inches smaller than the tub’s diameter, so a 6′ diameter tub only requires a 66” round or square concrete pad.

Saving 6″ on the pad means pouring less concrete as well as insuring that the pad won’t protrude any farther out than it absolutely has to. The typical thickness of the concrete pad should be 4″ with mesh wire reinforcement.

  1. The type of ground underneath the pad should be stable as well with 100% compaction. If the soil has a propensity for expanding and contracting due to extreme temperatures, you may be required to add concrete footings to stabilize the pad. Checking with a local contractor is an easy way to find out whether you need footings or not.
  2. The overall height of the tub is also a consideration. A 4′ tall standard hot tub will stand a roughly 50″ off the top surface of the concrete pad with some exceptions of our other tubs.

Based on this height, you may want to consider sinking part of the tub into the ground. Sunken tubs are extremely popular and are much easier to get in and out of.

In order to safely “sink” your tub, you will need to dig/construct a tub vault. The vault should have retaining walls to keep any excess dirt from eroding and coming into contact with the tub itself throughout its lifespan.

We recommend that there be a minimum 12″ clearance between the walls of the pit and the tub itself; a 5′ diameter tub will need a 8′ diameter pit. Another thing to keep in mind is that the tub will require a minimum of 24″, preferably 36″, of clearance around the entire tub. This will allow the tub to be assembled above the pit and then lowered down.

Indoor Installation Locations

Indoor installations aren’t that much different than outdoor installations, but they do require a few extra considerations.

The main consideration with indoor installations is moisture and the effect it has on other areas of your home.

  1. Moisture – It’s common practice to use hot tub insulated covers on outdoor hot tubs and the same is true with indoor hot tubs. Insulating covers save time, money and energy inside and outside, but quite a bit of steam is released when you take off an indoor cover.

Steam doesn’t play well with other interior sections of your house, so you need to make sure that the room your tub is located in has good air flow and very good ventilation to include possibly a motorized fan similar to a bathroom.

  1. Chemicals – Along with the steam factor, there’s also the issue of sanitation and the use of hot tub chemicals. Hot tubs that are used regularly need to be sanitized with chlorine, bromine or a non-chlorine shock treatment in combination with smaller amounts of chlorine or bromine.

These sanitizers can produce foul smelling odors that go well beyond the room your hot tub is located in. Ozone is another form of sanitizer that should not be used indoors. High concentrations of ozone can accumulate in the room that your tub is located in and cause severe throat irritations as well as corrode plastic and printed electronic circuitry.  A motorized fan should be installed to evacuate the off gassing from the room.

The best sanitizer to use indoors is an ionizer in combination with periodic non-chlorine shock treatments. One maintenance advantage to indoor installations is that less dirt, debris and pollen get into your tub which might save you a few dollars per year on sanitizers.

  1. Leaks – The other big moisture consideration is “leaks.” As much as we hate to admit it, the possibility of an indoor hot tub cracking, breaking or leaking does exist, and the odds increase as the tub gets older.

After years and years of use, a seal or gasket could wear out and cause anything from a small drip to a giant flood. We strongly recommend that indoor hot tub owners take special precautions by installing a waterproof flooring membrane and floor drain in the room that the tub and equipment are located in.

If the tub equipment is installed in a garage or basement, it’s a very good idea to set the equipment in a waterproof pan with a drain to insure that any possible leaks won’t damage surrounding items.