A.Energy and sustainable design consultant Andy Shapiro responds: The tables at right are based on seasonal delivered efficiency. Because it accounts for equipment, pipe, duct, and other losses, seasonal heating efficiency is lower (by about 5% to 15%) than the listed efficiency of the equipment (the AFUE, or annual fuel utilization efficiency) or the steady-state tested efficiency.

Efficiencies for oil equipment range from 50% for lower-efficiency water heaters to 85% for the best oil furnaces and boilers. Older boilers typically have seasonal efficiencies around 70%.

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