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<p>rating. Higher AFUE ratings indicate a more efficient furnace. Environmental impacts are a concern with heating systems, especially those that burn fossil fuels. The use of sustainable energy sources and energy-efficient systems is encouraged to reduce greenhouse gas emissions. The main source of harmful greenhouse gas emissions is the type of heating systems being used. For example, central heating systems depending on what they use to burn/electricity consumed to heat the system. Another environmental impact is during winter months heating</p><p>
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