An indirect-fired water heater that incorporates a single-wall heat exchanger shall be in accordance with the following requirements:
- The heat transfer medium shall be either potable water or contain fluids recognized as safe by the Food and Drug Administration (FDA) as food grade.
- Bear a label with the word "Caution," followed by
the following statements:
- The heat-transfer medium shall be potable water or other nontoxic fluid recognized as safe by the FDA.
- The maximum operating pressure of the heat exchanger shall not exceed the maximum operating pressure of the potable water supply.
- The word "Caution" and the statements in letters shall have an uppercase height of not less than 0.120 of an inch (3.048 mm). The vertical spacing between lines of type shall be not less than 0.046 of an inch (1.168 mm). Lowercase letters shall be compatible with the uppercase letter size specification.