Rising fuel costs have given an impetus to review the standby losses from both electric and gas-fired residential water heaters. Thermal energy losses from the hot and cold connecting lines during standby conditions have received attention as one opportunity for further reductions in energy use. Heat traps installed in both connecting lines have been suggested as one means for reducing standby losses.

Estimates of daily energy losses from two different piping configurations attached to one electric and one gas-fired water heater are now presented. Two different laboratory techniques were used to obtain the energy loss estimates for the water heaters tested. The piping configurations tested were made from nominal 1/2-in. copper tubing. No other sizes or pipe materials were tested. In the final section of this paper, experimental results from this study are compared to results from previous studies on connecting line losses.