To calculate the standby heat loss coefficient, we use the equation for heat loss from the DOE Energy Factor test procedure for water heaters, (US DOE 1993) as shown in Equation 6. where UA = standby heat loss coefficient (Btu/hr°F) EF = Energy factor of water heater RE = recovery efficiency of water heater Pon = rated input power of water heater (Btu/hr) Q_{out} = Energy content of water drawn from water heater during 24 hour test (41093.7 Btu/day)

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