co2online

co2online is a Berlin-based German nonprofit consultancy focused on household energy efficiency, climate protection and the reduction of carbon emissions. Legally operating as co2online gemeinnützige Beratungsgesellschaft mbH, the organisation was founded in 2003 by Johannes Hengstenberg. Its work is directed primarily at private households, although its projects also involve tenants, landlords, schools, municipalities, consumer organisations, public agencies and businesses in the energy-efficiency and building-modernisation sectors. The organisation's central proposition is that practical, data-supported advice can make climate protection more accessible while also reducing household energy bills. Its services cover everyday electricity saving, heating, hot-water consumption, building renovation and the replacement or optimisation of energy-consuming equipment. Rather than relying solely on general information, co2online uses interactive online tools, calculators, comparative databases, newsletters and the Energiesparkonto energy-saving account to help users understand their own consumption and identify potential actions. Its advisory model links individual consumption data with benchmarks and recommendations, allowing users to compare their performance with relevant reference groups. co2online operates at regional, national and, in some projects, European level. Its digital platforms are complemented by public information campaigns and structured programmes. The organisation's newsletter reportedly reaches approximately 150,000 users, while its website portfolio has generated millions of visits and online consultations. According to figures cited by the organisation, its services had delivered more than 23.4 million online consultations by 15 September 2025. In 2022, co2online reported 5.1 million website visits and estimated that its advice had contributed to the avoidance of 4.8 million tonnes of carbon dioxide emissions. These impact claims are presented within a broader evaluation framework developed with research institutions including the Institute for Energy and Environmental Research Heidelberg, the Institute for Ecological Economy Research, the Öko-Institut and the Wuppertal Institute. A major part of co2online's public role is the creation and communication of consumption benchmarks. In cooperation with the Deutscher Mieterbund, it publishes the annual Heizspiegel, a nationwide heating-cost and consumption comparison for residential buildings. The organisation also developed a nationwide electricity index, first published in 2014 with the Federal Ministry for the Environment and other consumer, research, energy-agency and trade-sector partners. The index uses aggregated household electricity data to establish comparative values. A hot-water consumption index was added in 2023 to make household hot-water use and savings opportunities more visible. co2online also works with the education sector. Since 2009, its Energiesparmeister competition has recognised school-based climate and energy projects involving pupils, teachers and educational staff. The programme has received thousands of applications and has awarded hundreds of schools. The organisation's campaigns and tools have received recognition including a European Commission Sustainable Energy Europe Award for the Klima sucht Schutz campaign, another for the ecoGator consumer application, and other awards related to sustainability, energy efficiency and educational impact. The company is not a conventional consumer-goods brand and does not primarily sell physical products. Its brand is instead associated with public-interest advice, energy data, climate communication and evidence-based household action. It is financed substantially through grants and contracts from German federal ministries, including the Federal Ministry of Economics, other federal ministries and the Federal Environment Agency. Around 50 employees were reported to work at its Berlin headqu…

co2online was established in Berlin in 2003 by Johannes Hengstenberg as a nonprofit organisation devoted to reducing household energy consumption and carbon emissions. From the beginning, its model combined public-interest communication with practical digital advice. Rather than positioning climate protection as an abstract policy issue, co2online sought to show households how changes in electricity use, heating, hot-water consumption and building efficiency could produce both environmental and financial benefits. The organisation developed an online advisory infrastructure consisting of guides, calculators, comparison tools, databases, newsletters and the Energiesparkonto energy-saving account. These services allow users to enter or monitor consumption information, compare it with reference values and receive recommendations tailored to their circumstances. The emphasis on household-level data helped establish co2online as an information intermediary between public policy, research findings and everyday consumer decisions. One of its best-known long-running activities is the Heizspiegel, a heating-cost and consumption comparison published with the Deutscher Mieterbund. The first nationwide analysis appeared in 2005, and subsequent editions provided comparative information for residential buildings. Municipal versions were also produced. The Heizspiegel became an important public communication instrument because it translated complex heating data into benchmarks that tenants, landlords and building owners could use when assessing consumption and possible modernisation measures. co2online's early work also included the Klima sucht Schutz campaign and the Heiz-Energiecheck. These activities attracted political criticism in the mid-2000s. A Bundestag inquiry questioned the distribution of subsidies and raised concerns about the necessity, effectiveness and accuracy of the heating advice. The Federal Ministry for the Environment rejected the criticism in a contemporaneous statement. In 2013, a separate controversy concerned the Stromsparinitiative, a government-supported electricity-saving campaign organised by co2online. Media coverage and parliamentary questions focused on the reported expenditure for an online platform and its comparatively limited use. The organisation expanded its work from advice into recurring national data products. In 2014 it published Germany's first nationwide electricity index in cooperation with the Federal Ministry for the Environment and a range of consumer organisations, research institutions, energy agencies and trade associations. The index used household electricity-consumption data to establish national comparative values. Later editions drew on a large number of observations, with the 2025 analysis described as using more than 360,000 data points. In 2023, co2online introduced a hot-water consumption index, extending its benchmarking approach to another significant household energy-use category. Education became another enduring area of activity. Since 2009, the Energiesparmeister competition has invited schools to submit climate-protection and energy-saving projects. The programme involves pupils, teachers and educational professionals and recognises projects at national level. It was designated an official project of the UNESCO-linked UN Decade of Education for Sustainable Development. By 2023, the competition had received 3,686 applications and awarded prizes to 222 schools. co2online's campaigns and digital tools received external recognition during its development. Klima sucht Schutz won the European Commission's Sustainable Energy Europe Award in the Awareness category in 2007. The organisation received a CleanTech Media Award in the Sustainability category in 2008. The Heizspiegel was presented by the International Energy Agency in 2009 as an innovative German activity in an international study. The ecoGator consumer application won a European Commission Sustainable Energy Europe Award in the Energy Efficiency category in 2015. In 2023, co2online received the Phineo Wirkt-Siegel, an effectiveness distinction. The organisation has remained primarily grant- and contract-funded rather than commercially financed. In 2022, its main funding came from the Federal Ministry of Economics, other federal ministries and the Federal Environment Agency. Around 50 employees were reported at the Berlin-Schöneberg headquarters, and Tanja Loitz was identified as managing director. By 2025, co2online stated that its online services had generated more than 23.4 million consultations. Its current identity is therefore that of a public-interest climate and energy advisory organisation whose principal assets are trusted information, longitudinal consumption data, digital tools and large-scale campaigns rather than physical consumer products.

1. 2025Latest electricity index analysis

   The latest cited electricity index analysis used more than 360,000 household consumption data points from Germany.

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2. 2023Hot-water consumption index launched

   co2online published its first hot-water consumption index, covering household consumption and savings potential.

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3. 2023Phineo effectiveness seal awarded

   The organisation received the Wirkt-Siegel from Phineo.

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4. 2021Annual impact reporting introduced

   co2online began publishing an annual impact report based on an assessment framework developed with several German environmental and energy research institutes.

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5. 2015ecoGator wins European energy-efficiency award

   The ecoGator consumer application received the European Commission's Sustainable Energy Europe Award in the Energy Efficiency category.

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6. 2014National electricity index introduced

   co2online published its first nationwide electricity index with government, consumer, research and industry partners.

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7. 2009Energiesparmeister launched

   co2online began its annual Energiesparmeister competition for school climate and energy-saving projects.

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8. 2009Heizspiegel recognised by the International Energy Agency

   The IEA presented the Heizspiegel as an innovative German activity in an international study of energy initiatives.

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9. 2008CleanTech Media Award

   co2online received a CleanTech Media Award in the Sustainability category.

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10. 2007Klima sucht Schutz receives European award

    The Klima sucht Schutz campaign won the European Commission's Sustainable Energy Europe Award in the Awareness category.

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11. 2005First nationwide Heizspiegel published

    co2online and the Deutscher Mieterbund published the first nationwide heating-cost and consumption comparison for residential buildings.

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12. 2003co2online founded in Berlin

    Johannes Hengstenberg founded the nonprofit co2online consultancy to encourage households to reduce energy consumption and carbon emissions.

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A nonprofit, data-driven public-interest organisation that translates energy and climate information into practical advice for households, schools and other stakeholders.

• EnergiesparkontoDigital energy-management tool

  The Energiesparkonto is a digital account that enables households to record and monitor energy consumption. It is intended to make electricity, heating and other household energy patterns more visible over time, compare them with suitable benchmarks and identify practical opportunities for reducing consumption, costs and emissions.

• HeizspiegelHeating benchmark and advisory service2005

  The Heizspiegel is an annual heating-cost and consumption comparison for residential buildings, produced with the Deutscher Mieterbund. It provides reference values that tenants, landlords and building owners can use to assess heating performance, identify unusually high consumption and consider efficiency improvements or building modernisation.

• National electricity indexHousehold electricity benchmark2014

  The national electricity index analyses household electricity-consumption data to establish Germany-wide comparative values. It was developed with public-sector, consumer, research, energy-agency and trade partners and is designed to help households understand whether their consumption is relatively high or low and where savings may be possible.

• Hot-water consumption indexHot-water benchmark2023

  Introduced in 2023, the hot-water consumption index presents current information about household hot-water use and potential savings. It extends co2online's benchmarking approach beyond heating and electricity to another recurring source of household energy demand.

• EnergiesparmeisterSchool climate-protection programme2009

  Energiesparmeister is an annual German competition for schools. Pupils, teachers and educational staff submit projects focused on energy saving and climate protection. The programme highlights practical school-based initiatives and has developed into one of co2online's principal education and engagement activities.

• ecoGatorConsumer application

  ecoGator was a consumer-oriented application associated with energy-efficiency advice. Its recognition in the European Commission's Sustainable Energy Europe Awards reflects co2online's use of digital tools to help consumers make more informed energy-related decisions.

• 2013Stromsparinitiative

  Germany

  A government-supported electricity-saving initiative organised by co2online that used an online platform to promote lower household electricity consumption.

  Outcome. The initiative attracted criticism concerning the reported cost of its online platform and its limited usage.

  Source
• 2009Energiesparmeister

  Germany

  An annual competition recognising school projects that address energy saving and climate protection, involving pupils, teachers and educational staff.

  Outcome. By 2023, the competition had received 3,686 applications and awarded prizes to 222 schools.

  Source
• 2003Klima sucht Schutz

  Germany

  A public climate-protection campaign that used online advice and household-oriented communication to connect carbon reduction with practical energy-saving measures.

  Outcome. The campaign won the European Commission's Sustainable Energy Europe Award in the Awareness category in 2007.

  Source

• 2023Launch of the hot-water consumption indexProduct launch

  Hot-water use represents a distinct household energy demand that is not fully captured by separate heating and electricity comparisons.

  What changed. co2online published a dedicated index showing hot-water consumption and potential savings.

  Aftermath. The new benchmark broadened the organisation's household-consumption advisory portfolio.

  Source
• 2021Formalisation of annual impact assessmentStrategy

  The organisation sought to assess the environmental and economic effects of its advisory services more systematically.

  What changed. co2online began presenting an annual impact report using an assessment approach developed with German energy and environmental research institutes.

  Aftermath. Impact reporting became part of the organisation's public account of emissions reductions and wider effects on households and related industries.

  Source
• 2014Launch of the national electricity indexProduct launch

  Household electricity consumption lacked a widely communicated national benchmark that consumers could use for comparison.

  What changed. co2online introduced a Germany-wide electricity index with public-sector, consumer, research, energy-agency and trade partners.

  Aftermath. The index became a recurring data-analysis product, with later editions using hundreds of thousands of consumption observations.

  Source

• 2025Latest national electricity index data analysis

  co2online reported a further national electricity-consumption analysis based on more than 360,000 household electricity data points from across Germany.

  Product generation
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• 2023First hot-water consumption index published

  co2online introduced a hot-water consumption index intended to show household consumption levels and potential savings.

  Product launch
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• 2022co2online reports millions of tonnes of avoided emissions

  co2online reported 5.1 million website visits and estimated that its advice had helped prevent 4.8 million tonnes of carbon dioxide emissions.

  Other
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• 2013Criticism of the Stromsparinitiative's online platform

  The co2online-organised Stromsparinitiative came under criticism after parliamentary questions and media reporting focused on the reported cost of its online platform and its limited use.

  RegulationOther
  Source
• 2005Criticism of publicly supported online energy advice

  The Klima sucht Schutz campaign and Heiz-Energiecheck were criticised in a Bundestag parliamentary inquiry over the allocation of subsidies and questions concerning the necessity, effectiveness and targeting of the heating advice service.

  RegulationOther
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1. Co2online
2. co2online official website