Spain faces a substantial gap in energy efficiency, with more than eighty percent of its buildings failing to meet current standards and earning energy certificates of E or F in the latest Population and Housing Census from the National Institute of Statistics (INE). This gap highlights the urgent need to decarbonize the housing stock, particularly by removing aging heating systems such as central diesel and coal boilers from service.
Even in the modern era, Spain retains a notable share of outdated heating solutions. The country hosts more than 140 coal-fired boilers and about 9,750 kerosene boilers in operation. These devices contribute to ambient air pollution, especially in large urban centers, and are a central focus for reform efforts aimed at cleaner air.
Coal boilers release roughly 216 mg per kWh of PM10 particles (those under 10 microns), while diesel boilers emit about 18 mg per kWh. By comparison, natural gas-fired boilers emit only around 0.7 mg per kWh. Sulfur oxides (SOx) follow a similar pattern, with coal producing 1,577 mg per kWh and diesel 340 mg per kWh, whereas natural gas contains no sulfur compounds, lowering these harmful emissions. This contrast underlines the cleaner profile of gas-fired systems.
Urban air quality becomes more at risk when road traffic emissions are added to these figures. In areas south of Madrid, including Getafe, Leganés, Fuenlabrada, and Aranjuez, the daily PM10 limit of 50 micrograms per cubic meter has been exceeded in recent weeks. Annual limits have not yet been breached, but the Barcelona Metropolitan Area experiences frequent breaches in dense neighborhoods like Eixample and in suburban centers such as Granollers or Montcada i Reixac.
Reducing pollutant emissions supports environmental protection and public health. The ongoing phase-out of coal and diesel boilers directly lowers emissions and reduces energy-intensive resource extraction for coal mining and diesel production. Current policies limit solid fossil fuels for building heating, and several administrations have launched renovation programs to remove the most polluting boiler rooms.
Policy discussions prominently feature renewal grants. Salamanca currently has the highest number of polluting coal and diesel boilers, followed by Leon and Madrid. In Madrid, public assistance helps replace old boilers with natural gas systems, with subsidies covering up to eighty percent of the total cost under the Boiler Rooms Renovation Plan within Madrid 360. This plan supports converting coal, kerosene, or other polluting fuels to modern condensing boilers that run on natural gas, with incentives capped by installed boiler power at just over fourteen thousand euros.
Regionally, the Madrid Community has also introduced a program offering up to three hundred fifty euros for residents who replace old boilers with more modern, efficient units to lower energy use. The measure targets around fifteen thousand households and could cut household gas consumption by roughly twenty percent. Other autonomous communities, including Asturias, Galicia, Catalonia, and the Basque Country, have similar relief schemes as part of broader energy rehabilitation initiatives tied to European Next Generation funds.
Replacing an old boiler yields clear advantages, both financially and environmentally. In recent years, natural gas boilers have benefited from advances that improve safety and efficiency, while coal-fired boilers have remained largely unchanged. A switch from a centralized heating system to individual units is often feasible, giving residents direct control over heating and hot water usage.
Financially, the transition pays off over time. Coal-fired systems require regular technician visits to keep the boiler running, driving up service costs and community fees. Natural gas, by contrast, emits about thirty-six percent less pollution than coal and features improved safety through newer technology and biannual inspections. Condensing boilers, capable of reclaiming latent heat from water vapor, have become standard in Europe since 2015 and are encouraged by renovation plans to replace central rooms or older individual boilers.
Thanks to condensation technology, modern boilers can reduce energy consumption by roughly thirty percent, lowering gas bills and reducing emissions while operating more quietly. In the longer term, the era of coal and diesel boilers is ending. This shift benefits the environment and enhances residents’ quality of life. The Madrid 360 plan anticipates halving gas and oil boilers by 2027, with nitrogen oxides reductions totaling about ninety tons annually in Madrid, marking a meaningful step toward more sustainable, healthier cities as reported by INE and environmental assessments.