## 5.11 B7.8. Jacket Loss

The hourly jacket loss for the lth unfired tank or indirectly fired storage tank in the kth system is calculated as

HJL = TSA l × ∆TS + FTL l RTI + REI l l l | Equation 40

where

HJLl = The tank surface losses of the lth unfired tank of the kth system TSAl = Tank surface area (ft2), see Equation 41.

∆TS = Temperature difference between ambient surrounding tank and hot water supply

temperature (ºF). Hot water supply temperature shall be 124ºF. For tanks located inside conditioned space use 75ºF for the ambient temperature. For tanks located in outside conditions use hourly dry bulb temperature ambient.

FTLl = Fitting losses. This is a constant 61.4 Btu/h.

REIl = R-value of exterior insulating wrap. No less than R-12 is required.

RTI l = R-value of insulation internal to water heater. Assume 0 without documentation.

Tank surface area (TSA) is used to calculate the hourly jacket loss (HJL) for unfired or indirectly fired tanks. TSA is given in the following equation as a function of the tank volume.

T SA = (1.254 ×VOL 0.33 + .531)2 l l | Equation 41

where

VOLl = Tank capacity (gal).