A Historical Document on the Advent of Tankless Water Heaters & Combi Boilers

Presented by Mr. Tankless — Your Trusted Experts in Tankless Technology www.mrtankless.net |

I. The Birth of an Idea: Early Conception

Benjamin Waddy Maughan, a painter in London, England, invented the first instantaneous water heater, which he named the “Geyser.”
The device heated water as it flowed through pipes exposed to hot gases from a burner
This was the earliest conceptual ancestor of the modern tankless water heater
Limitation: It had no flue to vent gases, making it dangerous for indoor use

Edwin Ruud, a Norwegian-born mechanical engineer working in Pittsburgh, Pennsylvania, designed the first automatic storage tank water heater
While Ruud’s innovation moved toward tank-based systems, his work laid engineering groundwork that would later circle back to tankless designs
His company, Ruud Manufacturing, became a household name in the water heating industry

In Germany and Japan, engineers began experimenting aggressively with instantaneous gas-fired water heaters
European homes, typically smaller and with limited utility space, demanded compact, space-saving solutions — making tankless designs a natural fit
German manufacturers such as Junkers & Co. (founded by Hugo Junkers) began producing early wall-mounted, gas-fired instantaneous water heaters as early as 1894

Japan emerged as a pioneer in tankless water heater technology, driven by:
- Limited residential space
- Cultural emphasis on bathing and hot water
- Resource conservation mindset
Companies like Rinnai (founded 1920) and Noritz (founded 1951) began developing and refining gas-fired tankless units for the Japanese domestic market

Post-WWII reconstruction in Europe and Japan accelerated the adoption of on-demand water heating
Units became more reliable, safer, and efficient
Germany, Italy, and Japan became the world’s testing grounds, with millions of units installed in residential homes
Gas safety standards and venting regulations were developed during this era

British and European engineers conceived the combination (combi) boiler — a single unit that provides both domestic hot water AND central heating
Key milestone: The combi boiler eliminated the need for:
- A separate hot water storage cylinder
- A cold water storage tank in the attic
- A separate boiler for radiators
By the late 1970s, combi boilers began dominating the UK and European market
Worcester Bosch, Vaillant, Baxi, and Ideal became leading combi boiler brands

By 1985, combi boilers accounted for a rapidly growing share of new boiler installations in the United Kingdom
Today, combi boilers represent over 70% of all new boiler installations in the UK
Condensing technology was introduced, pushing efficiency ratings above 90%

Companies like Navien, Rinnai, Noritz, and NTI began marketing combi boilers aggressively in the United States and Canada
The North American market was slower to adopt due to:
- Entrenched tank water heater infrastructure
- Larger homes with different heating layouts
- Lack of trained installers (more on this below)
However, adoption is accelerating rapidly, especially in:
- Smaller homes and condominiums
- New construction projects focused on energy efficiency
- Regions with access to natural gas

Rinnai entered the U.S. market in 1997, introducing Japanese-engineered tankless water heaters to American consumers
Noritz followed shortly thereafter, establishing U.S. operations in 2002
Navien entered the U.S. market in 2006, introducing condensing tankless technology at competitive price points
Takagi also became a major player during this period

The U.S. Department of Energy began promoting tankless water heaters as part of energy conservation programs
ENERGY STAR® certification was extended to qualifying tankless models
Federal and state tax credits and rebates incentivized homeowners to make the switch
By 2010, tankless water heaters captured approximately 15–20% of the U.S. water heater market and growing

Tankless technology became increasingly mainstream
Smart home integration, Wi-Fi diagnostics, and recirculation technology enhanced user experience
Condensing tankless units achieved thermal efficiency ratings of 95–98%, far surpassing traditional tank heaters (typically 60–70% efficient)

Unlike traditional tank heaters that deplete a stored supply, tankless units heat water on demand, as it flows through the unit
This means your shower never runs cold — whether you’re the first person in or the fifth
Families, multi-bathroom homes, and anyone who values comfort will never go back to a tank

Where natural gas is available, tankless and combi units offer dramatic energy savings:
- Traditional tank heaters suffer from standby heat loss — they constantly burn gas to keep 40–75 gallons of water hot, 24 hours a day, even when no one is using it
- Tankless units only fire when a hot water tap is opened, eliminating standby loss entirely
- Homeowners typically see 20–40% reduction in natural gas usage for water heating
- Condensing tankless models extract additional heat from exhaust gases, pushing savings even higher
Over the 20+ year lifespan of a tankless unit (compared to 8–12 years for a tank), the cumulative savings are substantial

Tankless units mount on a wall and are roughly the size of a small suitcase
Combi boilers eliminate multiple pieces of equipment (hot water tank + boiler) into one compact unit
Free up valuable garage, closet, or basement space

Lower natural gas consumption means reduced carbon emissions
Less material waste over time — one tankless unit outlasts 2–3 tank water heaters
Reduced water waste — hot water arrives faster with recirculation systems

Tankless and combi units cost more to purchase and install than traditional tank water heaters
However, the longer lifespan (20+ years vs. 8–12 years) and ongoing energy savings more than offset the initial investment over time
Think of it as an investment, not an expense

This is a well-known phenomenon in tankless systems:
- When a hot water tap is turned off and then quickly turned on again, there may be a brief temperature fluctuation.**