1. (1) Water heater means an automatically controlled vessel designed primarily for heating water or heating and storing water to provide hot water service for domestic or sanitary purposes.
2. (2) Recovery efficiency or thermal efficiency means the ratio of the heat absorbed by the water to the heat input delivered to the heating unit during the period that the water temperature is raised from the initial temperature to the final water temperature.
3. (3) Standby loss means the heat loss occurring while maintaining the final water temperature, over periods when no hot water is being drawn from the water tank.
4. (4) Energy factor means the overall efficiency of a water heater based on its recovery efficiency, standby loss and any auxiliary power input.
5. (5) Smoke spot number means the number corresponding to the spot on the Bacharach smoke scale, or other equivalent smoke scale, most closely matching the shade of a test spot, which is obtained by pulling a fixed volume of flue gas through a fixed area of standard filter paper.
6. (6) Stored thermal energy means the amount of energy measured in Btu stored in the water heater, calculated as the product of the manufacturer's specified storage capacity, the temperature difference between the initial and final water temperatures and the specific heat of water.

7. (7) Testing standard or TS means the testing standard referenced in Part 7816 of this Title to be used for determining compliance with this section.

   (b) Standards and testing requirements.

8. (1) Electric storage water heaters subject to United States Department of Energy appliance efficiency test procedures shall have an energy factor no less than.93 -.0013V, where V equals the manufacturer's specified storage capacity in gallons, when calculated and tested in accordance with the procedures specified in TS-4a.
9. (2) All other electric storage water heaters shall have a standby loss not in excess of four watts per square foot of the net surface area of the water heater when tested in accordance with TS-4a. The net surface area of the water heater is equal to the sum of twice the mean cross-sectional area and the product of the length of the mean cross-section and the mean perimeter of the water heater, discounting any area which deviates from a regular geometric figure.
10. (3) Gas-fired water heaters subject to United States Department of Energy appliance efficiency test procedures shall have an energy factor no less than.6 -.0019V, where V equals the manufacturer's specified storage capacity in gallons, when calculated and tested in accordance with the procedures specified in TS-4a.
11. (4) Oil-fired water heaters subject to United States Department of Energy appliance efficiency test procedures shall have an energy factor no less than.59 -.0019V, where V equals the manufacturer's specified storage capacity in gallons, when calculated and tested in accordance with the procedures specified in TS-4a.
12. (5) All other gas-fired and oil-fired storage and nonstorage water heaters shall have a minimum thermal efficiency of 75 percent, when tested in accordance with TS-4b. In addition, all other gas-fired and oil-fired storage water heaters shall have a standby loss not in excess of a percent of the stored thermal energy equal to 2.3 plus the quotient of 67 divided by the manufacturer's specified storage capacity in gallons, when tested in accordance with TS-4b. With respect to oil-fired water heaters, testing shall assume a higher heating value of at least 138,500 Btu per gallon, the draft settings shall be in accordance with the manufacturer's specifications, and the smoke level in the flue shall not exceed a smoke spot number of one.

(a) Definitions.