The energy factor for gas-fired and electric storage water heaters is a derived shipment-weighted efficiency based on the year the equipment was purchased (Table 12). This number is the average efficiency for all units sold within a particular year weighted by the number of units in each efficiency bin (GAMA 1996). For LPG-fired water heaters, we assumed the same energy factor as for natural gas-fired units. For fuel oil-fired units, we assumed an energy factor of 0.54 before 1990 and 0.59 after 1990 (Lutz, personal communication).For instantaneous water heaters the energy factor will be determined by de-rating the efficiency by 7% from manufacturer's data 
Source: GAMA Directory.
Note: Energy Factor for Water Heaters is percentage efficiency divided by 100.
Note: yellow cells contain data held constant from previous real data point.
Note: In 2004, a new standard for water heaters went into effect (green cells).
 Reference: http://fsec.ucf.edu/en/publications/pdf/FSEC-CR-1856-10.pdf, (see Fig E-4)
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