Scientific Facts About Ozone Use in Hot Tubs

What is Ozone?


• Ozone is “active oxygen”, nature’s special element. Each ozone molecule consists of three oxygen atoms.
• Ozone is a natural purifier.
• Ozone is created in nature by the combination of oxygen in air and the ultraviolet rays of the sun or by the corona discharge during a lightning storm.
• Ozone has a clean, fresh scent noticed after a rainstorm.
• Ozone is the most powerful oxidizer safely used.
• Ozone is the alternative water purifier to traditional chemicals such as chlorine and bromine.

What Does Ozone Do?

• The Ozone layer in the atmosphere protects the earth from deadly radiation.
• Ozone destroys bacteria, viruses, mold and mildew.
• Ozone eliminates spores, cysts, yeast and fungus.
• Ozone oxidizes iron, sulfur, manganese and hydrogen sulfate.
• Ozone eliminates oils and other contaminants in water.
• Ozone eliminates odors in air, such as smoke.
• Ozone keeps water clean and sparkling clear.
• Ozone keeps water fresh.

Ozone is Healthy

• Ozone leaves no chemical by-products in water.
• Ozone leaves no chemical taste or smell.
• Ozone will not burn eyes or make them red or irritated. Ozone will not irritate or dry out skin, nose, or ears.
• Ozone will not leave a chemical film on material or skin.
• Ozone will not discolor or damage hair or clothing.
• Ozone adds no contaminants or by-products to water. Ozone rids water and air of unhealthy microorganisms.
• Ozone is NOT a carcinogen.

Where is Ozone Used?

• Nice, France built the first water purification plant to use ozone in 1906
• Los Angeles has the largest ozone drinking water treatment plant in the world.
• Most bottled water is purified by ozone.
• Ozone is used to clean waste water and toxic waste.
• Ozone purifies water in wells and home drinking water systems.
• Ozone systems have brought life back to “dead” contaminated lakes and pools.
• Ozone is used to purify air in hotel rooms, boats, RVs, cars and smoke/fire damaged structures.
• Ozone is used in thousands of residential and commercial pools, hot tubs and spas all over the world.

How is Ozone Made?


Ozone Is Safe for the Environment as well as Spa & Pool Equipment

• Ozone will not explode.
• Ozone is not a fire hazard.
• In the dose required for excellent purification, ozone does not produce harmful fumes.
• Ozone will not damage plumbing fittings or pipes.

Ozone Is Convenient for Hot Tubs, Spas & Pools

• Ozone does not have to be purchased or stored. Ozone is generated “on site” and is introduced into the water or air automatically.
• Ozone does not affect the pH balance of water, thus minimizing pH adjustments.
• Ozone helps reduce total dissolved solids in water so that the water does not have to be changed as often.
• Ozone eliminates much of the routine maintenance because it does such an effective job keeping the water clean.

Information About Chloramines

When any type of chlorine is added to water, it usually forms hypochlorous acid (HOCl), the most powerful killing form of chlorine in water, and hypochlorite ion (OCl-), a relatively weak form of chlorine in water.

The percentage of HOCl and OCl- is determined by the pH of the water. As the pH goes up, less of the chlorine is in the killing form and more of the chlorine is in the weaker form. The total of HOCl and OCl- is the free available chlorine.

Chlorine can combine with ammonia and nitrogen compounds in the water to form chloramines, sometimes called combined chlorine. By combining with ammonia and nitrogen, free chlorine in the water is disabled.

Chloramines are 60 to 80 times less effective than free chlorine. Chloramines are formed any time ammonia and nitrogen are in the water. Some of the ammonia and nitrogen compounds are introduced into the water by swimmers and bathers in the form of perspiration, urine, saliva, sputum and fecal matter.

An active swimmer sweats one pint per hour. The average person sweats three pints per hour in a heated spa. Ammonia and nitrogen compounds are also introduced into the water by rain. Each drop of rain has some dissolved nitrogen from our atmosphere and from automobile emissions.

Chloramines smell bad. This is the smell most often associated with pools and spas in health clubs and YMCAs. Chloramines are eye and skin irritants, and they cloud the water.

Chloramines can be removed from the water by the following three methods:

1. Chlorine Shock Treatment or Super-Chlorination: By adding a mega-dose of chlorine. Usually 3 to 6 times more chlorine than a normal dose is added to the water, or the level of chlorine is raised to 5 to 10 ppm and held there for 4 hours.

This is called super chlorination. To remove chloramines, the ratio of chlorine to ammonia must be at least 7.6 to 1. If this ratio is not obtained, then more chloramines will be produced. Swimmers and bathers should not enter the water until the level of chlorine has dropped to 3 ppm or less.

2. Non-Chlorine Shock Treatment: By adding a non-chlorine shock to the water. The most common chemical used for this is potassium peroxymonosulfate.

3. Adding Ozone to the Water: If an ozone generator is installed on a pool or spa, then oxidation of the ammonia and nitrogen compounds will take place whenever the ozone system is operating. The longer the system operates, the more the ozone can destroy the ammonia and nitrogen.

Ozone oxidizes soap, deodorant, hair spray, cologne, makeup, perfume, body lotion, hand cream, sun tan lotion, saliva and urine. In addition, ozone kills all pathogenic bacteria, germs and viruses.

Ozone takes care of the big job of oxidizing all these organic contaminants. Ozone frees up the combined chlorine, thus leaving the chlorine free to provide a residual. Ozone ultimately enhances the performance of chlorine and bromine.

Less chlorine or bromine will be needed to maintain a residual. Commonly, ozone reduces chlorine or bromine use by 60-90 percent. The quality of water will be dramatically better with the combination of ozone and chlorine or the combination of ozone and bromine than with chlorine or bromine alone.

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.

Chofu Wood Burning Water Heaters & Wood-Fired Hot Tub Systems

This is the perfect heater and hot tub system for cabins, those that are off grid, or if you’re simply looking for something a little more rustic or “back to basics”.

Like our regular complete hot tub systems, our wood fired hot tub systems are available in western red cedar, Alaskan Yellow Cedar or teak.

The Chofu is a precision built wood-burning water heater specifically designed for heating hot tubs. It circulates water using the principal of thermo-siphon (the movement created by rising hot water)and eliminates the need for a circulating pump or electricity.

This unique feature opens up a whole new range of possibilities for alternative hot tubs. Now you can have a traditional wooden soaking hot tub without the need for pumps or electricity.

The Chofu utilizes a sophisticated heat exchange design for efficient water heating. The stainless steel stove body surrounding the firebox is a double-walled water-jacket with a 1-inch space between. This makes the entire firebox (except the front) a heat-transferring surface.

Additional heat transfer takes place in a water-filled baffle plate that runs horizontally through the firebox. The baffle deflects the path of the fire, so it gives up more heat into the water jacket before going up the chimney.

The Chofu will connect to any tub using accessories provided flexible neoprene tubes, stainless steel pipes, and thru-wall tub ports. (Thickness of the tub wall must be specified to determine the length of thru-wall ports.)
Installation requires these four basic steps:

  1. Preparing a brick or cement foundation next to the hot tub to receive the Chofu heater.
  2. Cutting 2-1/2″ holes in the side of the hot tub for thru-wall ports.
  3. Installing pipes to connect heater and tub.
  4. Installing the stove pipe (8 feet recommended).

Operation – The Chofu operates like a conventional wood stove, achieving its fastest heating rate from dry hardwoods. It uses wood up to 17″ long and has an 18″ x 14″ x 14″ firebox. The most efficient heating comes from using 17″ x 1½” x 1½”, loaded at 45 min. intervals.

The Chofu hot tub heater has a high and low speed draft control to regulate the heating rate. It operates with the draft wide open for fast heating, and closed down to maintain temperature once the water is hot.


  • High grade stainless steel stove body
  • 1/8-inch steel stove front
  • Heavy cast iron door and grates
  • Hot Tub Connection kit
  • Generous size firebox, 18″L x 14″W x 10″H
  • Vented smoke-outlet for secondary combustion.
  • ¾” drain for freeze protection.
  • An ash drawer for easy removal of ashes.
  • A long handled ash rake


  • Dimensions: 16″ wide x 23″ long x 18″ high
  • Weight: 59-lbs.
  • Stove body: Grade 316 stainless steel, inner wall 20-gauge, outer wall 22-gauge
  • Stove Front: 1/8-inch steel
  • Firebox door and grates: cast iron
  • Firebox dimensions: 18″L x 14″W x 10″H
  • Heat exchange surface area: 9 sq. ft.
  • Smoke outlet: 4 5/8-inch (reduced to 4-inch)
  • Circulating pipes: 1¾” O.D.
  • Drain: ¾” I.D.

Heating Rate Information – Although the heating rate is variable depending on dryness and type of wood, frequency of loading, etc., the average heat output of the wood burning Chofu hot tub heater is 32,000 BTU’s (an 11kW electric heater is about 30,000 BTU’s). A 200 gallon hot tub can be heated at approx. 20ºF per hour.

Note: The heat output of the Chofu increases after an initial 45-min. warm-up period that heats the stove body and establishes a bed of coals.

Heating Rate

Hot tub size…
diameter x height
Gallonstemp. rise per hour
*We don’t recommend this large a hot tub due to the extended heat-up time

Most Requested Upgrades & Accessories

Stainless Steel Stovepipe – Made of grade 304 stainless steel. 8ft of pipe is necessary to produce the optimum air-draw through the stove for a fast, efficient heating rate; a shorter length will produce a slower heating time.

Using more than 8ft of pipe produces a hotter fire but will reduce fuel efficiency because more of the flame is drawn up into the chimney. Remedy this by installing a stove damper. If more than 8ft of pipe is used, it must be supported to insure stability.

Sheet metal screws and a cobalt drill bit are provided with the Chofu Wood-fired Heater for fastening stove pipe connections.

Stainless Steel Chimney Cap – Made of grade 304 stainless. Maybe necessary where danger of fire is extreme, however, secondary combustion in Chofu prevents most sparks from escaping chimney.

Adding a chimney cap reduces draw through stove, slowing the heating rate. 10ft or more of pipe is necessary when using a chimney cap, to maintain maximum heat rate. Stovepipe with a chimney cap must always be supported to provide stability.

Filtration/Circulation System – This high performance pump/filter skid pack is rated at 2400 gallons per hour and consists of an energy efficient 120v Hayward Power-Flo pump and Micro Star-Clear filter, all pre-plumbed and mounted to a molded base. Designed for outdoor applications, simply plug it into a GFCI protected outlet and add a timer if desired.