Copyright Goodheart-Willcox Co., Inc. 54 Hydronic Heating: Systems and Applications electric boilers have close to perfect energy efficiency, electricity costs in most areas outweigh the cost of other fossil fuels such as natural gas, oil, or LP. Remem- ber to compare the costs of various heating fuels in your area before making a purchasing decision. 3.7 Low NOx Boilers Nitrogen Oxides (NOx) belong to a family of poisonous, highly reactive gases. These types of gases form when fuels are burned at high temperatures. NOx is emitted from various sources, including automobiles, power plants, and indus- trial boilers. It often appears as a brownish gas, with a strong oxidizing agent that can play a major role in atmospheric reaction with organic compounds, causing smog and acid rain. For this reason, certain parts of the United States and Canada require the specifications of new boilers to include low-NOx burner emission levels. The key to producing a low-NOx boiler is effective burner design. Low NOx burners control the mixing of air and fuel at each burner, creating larger flame patterns. This reduces the peak flame temperature, which in turn significantly reduces the level of NOx produced by each burner, Figure 3-23. GREEN TIP Are Electric Boilers Truly Environmentally Friendly? While electric boilers are generally considered environmentally friendly since they do not produce combustion gases, there are concerns that the initial process of generating the source electricity at its fossil fuel-generated power plant can create as much pollution as a gas-fired boiler system, therefore negating the environmentally friendly aspects. This does not, of course, take into account that wind, solar, or nuclear power may be used to generate the electricity. However, when contemplating sources of renewable energy for electrical power generation, you should consider that the wind does not always blow, the sun does not always shine, and the last nuclear power plant in the US was built 30 years ago. Possibly the best approach to environmental stewardship relies on individual choices that best fit individual applications. Fuel-rich core Air Fuel gun Primary air Secondary air Tertiary air Primary reaction zone Primary air and fuel mix to create fuel-rich flame core Goodheart-Willcox Publisher Figure 3-23. This illustration shows how controlling the mixing of air and fuel at each burner results in low NOx emissions.