505.4 Indirect-Fired Water Heaters. Indirect-fired water

heaters shall be in accordance with the applicable sections of the ASME Boiler and Pressure Vessel Code or shall comply with one of the other applicable standards shown in Table 501.1(1). Each water heater shall bear a label in accordance with ASME requirements, or an approved testing agency, certifying and attesting that such an appliance has been tested, inspected and meets the requirements of the applicable standards or code.

505.4.1 Single-Wall Heat Exchanger. An indirectfired water heater that incorporates a single-wall heat exchanger shall be in accordance with the following requirements: (1) 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. (2) Bear a label with the word “Caution,” followed by the

following statements: (a) The heat-transfer medium shall be potable water

or other nontoxic fluid recognized as safe by the FDA. (b) The maximum operating pressure of the heat

exchanger shall not exceed the maximum operating pressure of the potable water supply. (3) The word “Caution” and the statements in letters shall

84 2022 CALIFORNIA PLUMBING CODE

infiltration rate is known to be less than 0.40 ACH (air change per hour), the method in Section 506.2.2 shall be used. The total required volume shall be the sum of the required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section 506.3, are considered a part of the required volume. [NFPA 54:9.3.2]

506.2.1 Standard Method. The minimum required volume shall be 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m ³ /kW). [NFPA 54:9.3.2.1] 506.2.2 Known Air Infiltration Rate Method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows [NFPA 54:9.3.2.2]: (1) For appliances other than fan-assisted, calculate

WATER HEATERS

within 12 inches (305 mm) of the top of the enclosure and one permanent opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 506.3). The minimum dimension of air openings shall not be less than 3 inches (76 mm). (2) Combining spaces in different stories. The volumes of

spaces in different stories shall be considered as communicating spaces where such spaces are connected by one or more permanent openings in doors or floors having a total minimum free area of 2 square inches per 1000 Btu/h (0.004 m ² /kW) of total input rating of all appliances. [NFPA 54:9.3.2.3]

using the following Equation 506.2.2(1). [NFPA 54:9.3.2.2(1)]

[Equation 506.2.2(1)]

[Equation 506.2.2(1)]

ACH 1000 Btu/h

21 ft3 ( I other )

ACH

Required Volume other ≥ 21 ft3 (

(2) For fan-assisted appliances, calculate using the fol lowing Equation 506.2.2(2). [NFPA 54:9.3.2.2(2)]

[Equation 506.2.2(2)]

Required Volume fan ≥ ACH 1000 Btu/h

15 ft 3 ( I fan )

FIGURE 506.3 ALL COMBUSTION AIR FROM ADJACENT INDOOR SPACES

Where: Iother = All appliances other than fan-assisted input

in (Btu/h) Ifan = Fan-assisted appliance input in (Btu/h) ACH = Air change per hour (percent of volume of

space exchanged per hour, expressed as a decimal)

THROUGH INDOOR COMBUSTION AIR OPENINGS

[NFPA 54: FIGURE A.9.3.2.3(1)]