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Existing Fields – Air Bubble Technology

As part of our effort to create new value in existing fields, our Development Division has developed the industry's first residential-use water heater that provides hot water containing fine bubbles. Fine bubbles are further divided into ultrafine bubbles, micro-bubbles, and so forth depending on bubble diameter. We have designated the technology for generating fine bubbles from water heaters as "Air Bubble Technology" and are working to strengthen our expertise in this area.

We use Air Bubble Technology in our micro-bubble bath units and ultrafine bubble water heaters. It makes the daily bathing experience more relaxing and facilitates cleaning around the home's wet areas. With Air Bubble Technology, we provide new experiences to people's lives.

Air Bubble Technology

Features of fine bubbles (ultrafine bubbles and micro-bubbles)

Ultrafine bubbles are fine, colorless, and transparent and do not make the water cloudy, but they make removal of grime easier. Micro-bubbles, on the other hand, are larger than ultrafine bubbles and give water a cloudy white appearance, creating a visually relaxing effect. We apply the characteristics of each type of fine bubbles to our products according to their intended use.
Ultrafine bubbles Micro-bubbles
Bubble diameter Several 10s of nm–1µm
(Size of virus or smoke particle)
* 1µm = 0.001mm
(Size of cedar pollen or yellow dust particle)
Visual perspective Not visible
Transparent (not cloudy)
Bubble movement Remains in water for a long time
(Weeks to months)
Rises very slowly
(Approx. 3mm/minute for 10µm bubbles)
Disappears underwater

Rinnai appliances featuring fine bubble technology

Name of product Ultrafine-bubble (UFB) water heater Micro-bubble (MB) bath unit
Main product appearance
Main product appearance
Main product appearance

Our ultrafine bubble water heaters can deliver hot water containing ultrafine bubbles to various places where hot water pipes are connected, such as bathrooms, washrooms, kitchens, and dishwashers.

Our micro-bubble bath units are water heaters that generate minute air bubbles in the water to offer an enjoyable white-water bathing experience. They provide relaxation and skin hydration just like relaxing in a hot spring.


Areas connected with hot water pipes (such as bathrooms, kitchens, and washrooms)

Areas connected with hot water pipes (such as bathrooms, kitchens, and washrooms)


Bubble generation method

Venturi + Shear

Venturi + Static mixer

Pressurized dissolution

Pressurized dissolution + Swirling flow mechanism
Bubble flow

1. Changes the water pressure of the hot water to turn air in the water into bubbles
2. Shear bubbles by obstacles in the flow path

1. Draws hot water from the bathtub
2. Air is blended by pressurization and swirling flow in the tank
3. When water jets out from the circulation fitting, the pressure drops and air bubbles are formed

Amount of bubbles generated

Volume of ultrafine bubbles generated(per 1cc)
Heat source for gas water heater
22.6 million bubbles

Gas bathwater heater
22.6 million bubbles

Gas water heater
17.68 million bubbles

Volume of micro-bubbles generated(per 1cc)
Gas bathwater heater
30,000 bubbles

Volume of ultrafine bubbles generated(per 1cc)
Gas water heater
17.72 million bubbles

Value provided

Using hot water containing ultrafine bubbles prevents stains and limescale from forming in bathrooms, kitchens, washrooms, and other wet areas. They also prevent grime from sticking inside drainpipes, which are hard to clean, thus reducing the burden of daily cleaning.

(Grime build-up inside drainpipe)
(Grime build-up inside drainpipe)

The massive volume of bubbles creates a fine white cloudy water appearance like that of a hot spring, creating a relaxation effect. It also gently warms the body and makes the warm bath feeling last longer. According to feedback, moreover, it helps keep the skin hydrated, which indicates a moisturizing effect.

(Relaxation effect)
(Relaxation effect)
Main effects

1. Reduced dirt around wet areas
Compared with regular bathwater, the bacteria that cause stains are more easily washed away in ultrafine-bubble bathwater, allowing you to reduce stains in bathrooms and on kitchen sinks.

2. Reduced limescale stains
Compared with regular bathwater, ultrafine-bubble bathwater reduces adhesion of mineral components and inhibits limescale stains that are difficult to remove by normal cleaning.

3. Reduced drain-pipe contamination
Compared with regular bathwater, dirt is more easily washed away and the drain is kept clean.

4. Sustained moisture content in the stratum corneum of the skin
We have confirmed that ultra-fine bubble water keeps the moisture content in the stratum corneum of the skin. It is expected to maintain the moisture content of the skin.

1. Relaxation effect
Even for regular bathing, it has been reported that bathing in warm water helps relieve psychological tension and is also linked to better sleeping experiences.

2. Moisturizing effect
Micro-bubble bathing is thought to help maintain blood flow to the skin surface and keep the skin hydrated because, after bathing, the body temperature drops more slowly compared with bathing in regular water.

3. Warm bath effect
Because the body is enveloped by air bubbles, the transfer of heat from the water to the body slows down, which makes the body warm slowly. After bathing, the elevated body temperature dissipates gradually, making the body feel warm for longer.

4. Cleaning effect
Microscopic air bubbles adsorb and remove dirt from the skin. The air bubbles also adsorb and scrape away dirt and sebum that accumulate in pores, thereby keeping the skin clean. Tests have also shown that micro-bubble bathing has a higher dirt removal rate than regular bathing.

5. Support for falling asleep
Microbubble baths are expected to help people move into a state of relaxation more quickly than bathing in plain water. After bathing, the user may spend time before falling asleep in a more relaxed state.