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History and Vision

Norwegian roots and industrial adventure

A Norwegian business adventure through 3 generations:

The family business

The founder – Reidar Frölich Braathen – started “Oslo Sveisebedrift, Oslo” (OSO) in Oslo in 1932, as one of the first welding shops in Norway. Frölich Braathen was both a blacksmith and a lieutenant in the Norwegian air force and among the first in the country who mastered both electric and autogenous welding. With minimal resources he created the first Norwegian welded water heater. Thanks to his continuous innovation and dedication Frölich Braathen employed 100 people by 1940. His 50 years of experience became the foundation of OSO Hotwater AS – a Norwegian industrial adventure.

2nd generation – Chris Reidar Braathen – was very much involved in restoring the factory after the war. In 1964 Chris Reidar established OSO factory by the Drammen river, where the production of water heaters is still located today. Chris Reidar was a technician and had great commitment and drive, in addition to idealistic ideas. He has, during his more than 50 years in OSO, combined industry and environmental protection in a unique way and has given OSO the recognition as one of the leading environmental enterprises in the Nordic countries, something which has led to several environmental awards and accolades.

3rd generation – Sigurd Braathen – continues to lead OSO with a clear objective to still be a family business located in Norway. Dedicated to improving OSO products and processes, Sigurd continues to build the company brick by brick, and is proud of the fact that OSO has become one of the most robotized companies in Norway. The pioneering spirit lives on with product innovations featuring integrated solutions, ground-breaking material technology and added value for our customers.


  • NORWAY: Thanks to continuous innovation, trust and confidence from our customers, OSO is the clear market leader in Norway over the last 85 years. Our products delivers well-being through domestic hot water and space heating to two-thirds of all homes in the country, with exceptional lifetime economy.
  • OEM: We are proud to be a preferred supplier to many of the best-known brands in the heating industry, delivering our products throughout Europe.  OEM is an important part of our business because it inspires and motivates us to think innovatively, be flexible in our approach and challenge traditional mind-sets.
  • EXPORT: OSO focuses on the Nordics, UK, Russia, the US and Canada, as well as the shipping and offshore markets. Export sales make up about 50% of the turnover and gives us a unique perspective and knowledge of water qualities and product properties which benefits all our customers.

Historical milestones


  • 1932 Norway’s first autogenous welded storage tank is produced at Oslo Svesiebedrift.
  • 1935 Welded cooking pots and wood boilers complements the range of products.
  • 1938 Development of wood-burning boilers which provides both heat and hot-water.
  • 1941 Production of potato collector cogs and planting equipment during the war.
  • 1945 Production of copper-lined storage tanks 200 – 50,000 litres resumes.
  • 1955 Provision storage tanks tripled the capacity while only taken half the space.
  • 1957 “TRIPLEX” and “COMPACT” heating units for oil and wood/electrical units.
  • 1959 “NORTHERM” integrated heating unit and storage tanks is launched.
  • 1968 The “SAFE” system – triple-valve and surface mounted thermostat is introduced.
  • 1968 First in the world to produce stainless steel storage tanks which increases lifespan.
  • 1979 The “SUNSAVER” solar-heated storage tanks are launched.
  • 1980 Top-mounted mixing valves becomes standard, resulting in huge resource savings.
  • 1984 The tank-in-tank unit “PROGESSS” water heater line is introduced for heat pumps.
  • 1985 The “TURBO” system with plate exchanger revolutionises heat-up times.
  • 1988 The “EXPRESS” storage tanks with flip/flop thermostat heats water 3 times faster.
  • 1993 The “UNIVERSAL” el. boilers 15-45 kW without contactors simplifies installation.
  • 1994 “THERMO TOP” reduces heat loss from standard storage tanks by 20%.
  • 1999 The “MAXI” large storage tanks 500-1000 liters becomes industry standard.
  • 2001 The warranty is doubled on the stainless steel pressure tank.
  • 2004 The new “ECO FOAM” insulation saves more than 500 million kWh in 10 years.
  • 2007 “ENERGY SAVER” for grey water reuse results in huge Energy Efficiency savings.
  • 2008 The “OPTIMA” line triples the capacity and increases the efficiency for heat pumps.
  • 2010 “EXPANSION” is introduced with a fully integrated expansion solution.
  • 2012 “OPTIMA TRIPLE COIL” is the industry’s most advanced heating central.
  • 2015 The “DELTA” series receives rating “A” from ErP – best in class.
  • 2017 “NANOPUR” insulation and VACUUM panels saves 200 million kWh over 10 years.

OSO & The Environment: 50 years of effort

OSO was one of the first environmental enterprises in Norway with more than 50 years of efforts and investments to unite people, environment and industry. The emphasis on the environment started with Reidar Braathen Jr. in 1956. He created “The most environmental company in Scandinavia” (SCANVAC award). After 50 years of continuing effort for both indoor and outdoor environments, GRIP together with the Minister of Environmental Protection, Arild Hareide, awarded the special “Glassbjørn”-award to OSO for our effort to save the environment.

Thanks to the loyalty of our customers, OSO has become renowned for best practice for both its manufacturing of water heaters as well as environmental protection. Products with extremely long lifecycle, and the lowest heat loss of any storage tanks on the market are some of our biggest contributions to the environment, in addition to zero-emission production and no toxic waste released of any kind. Love and care for nature is the basis for our engagement in protecting the environment, our objective is the same today as 50 years ago: PROTECT OUR BEAUTIFUL PLANET.

Among the most important environmental efforts are:

  • 1968 – Europe’s first stainless steel water heater increased the lifespan of water heaters.
  • 1980 – Mixing valve increased efficiency by 30% and reduced the amount of steel needed.
  • 1990 – The first “Resirc-system” in Europe for discarded storage tanks.
  • 1990 – OSO establishes an annual NOK 100,000 “Bronseelgen”- environmental award.
  • 1994 – OSO is among the first companies to eliminate the use of CFC gases.
  • 1994 – Free bicycle to every non-smoking employee and a paid reward per kilometre.
  • 1994 – All company vehicles are converted to run on natural gas reducing emissions by 30%.
  • 1995 – Gives NOK 5 million to environmental purposes – establishing OSO environmental fund.
  • 2004 – ECO FOAM saves more than 500 million kWh in heat loss over 10 years.
  • 2010 – 10 million litres of water are saved in Energy Conservation efforts during production.
  • 2015 – The world’s best isolated storage tank – DELTA – is introduced.
  • 2017 – NANOPUR and VACUUM panels saves 200 million kWh over 10 years.

The OSO Environmental Fund has contributed to these projects:

  • Thor Heyerdahl: The documentary “Progress”
  • Bellona: The Russian Northern Fleet-campaign.
  • The Rainforest Fund: Save the rainforest.
  • Rein Dammann: “The call of the Wild”
  • Børge Ousland: “Alone across Artic” – climate research.
  • Lars Moxheim: The Sverdrup Expedition
  • New Paradigm Films: Project “Free Energy”

World-class production

OSO Hotwater AS is since 2015 the most robotized manufacturing company in Norway. This has been necessary to keep our business in Norway instead of moving production to low-cost countries as is done by many manufacturing companies these days. By leaving the heavy lifts and repetitive tasks to robots we have liberated the human resources for more constructive tasks, while in the process creating a working environment where health and wellbeing is in focus. OSO has won several awards for our working environment, and is certified in this area in accordance with ISO 45001.

Innovation timeline

Company philosophy​

Our vision: Stainless steel water heaters with class leading quality and efficiency

Strong partners

OSO collaborates closely with all leading players within distribution, installation and service in the HVAC field. Our products are used stand-alone or as part of a complete heating system in combination with air-water and liquid-water heat pumps, solar panels, district heating, gas- and electric-boilers. We always recommend that a licensed technician install our products, to ensure the end result provides hot water safely for decades to come.

Solid suppliers

OSO uses exclusively Norwegian, European or American suppliers for all critical-to-quality components. This is beneficial both for the customer and the environment for a product that should last 25 years. The best for dependability, material selection and technology is at the core when we choose our suppliers – both for the product and the process technology. That contributes to a more efficient use of resources and environmental protection.


Pioneering work in product development and continuing efforts to do the best for people and environment have resulted in a number of environmental awards and recognitions. Of particular importance has been the National Honorary Award “Glassbjørnen” (the Glass Bear) for unique environment efforts through 30 years, the “SCANVAC” award for the Best Environmental Company in Scandinavia and the “Best environment and Energy Efficiency product” for introducing foam insulated storage tanks. The accolades inspires us to further develop our vision of environmental protection.

Company Certifications

Certificates and approvals held by OSO Hotwater AS.

Print or download certifications here

Product certifications

OSO products are certified to relevant standards according to model and type.

OSO products are certified to relevant standards according to model and type.

  • CE — Product compliancy to European standards
    • ErP (Energy-related Products Directive) 
    • EMC (Electromagnetic Compatibility)
    • LVD (Low Voltage Directive)
    • PED (Pressure Equipment Directive)
    • RoHS (Restriction of Hazardous Substances)
    • REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals)
  • NEMKO — Compliancy with EU regulations & safety standards
  • WRAS — Compliancy with UK regulations & safety standards
  • AHRI — Certified efficiency rating to US HVAC standards
  • ETL — Compliancy with North American safety standards    
  • CSA — Compliancy with Canadian Electrical Code​ 

Marine and industrial products:

  • ABS
  • DNV GL