Section 160.4 – Mandatory Requirements for Water Heating Systems

(a)      Systems using gas or propane water heaters to serve individual dwelling units shall include the following components:

1.    A dedicated 125 volt, 20 amp electrical receptacle that is connected to the electric panel with a 120/240 volt 3 conductor, 10 AWG copper branch circuit, within 3 feet from the water heater and accessible to the water heater with no obstructions.  In addition, all of the following:

A. Both ends of the unused conductor shall be labeled with the word “spare” and be electrically isolated; and

B. A reserved single pole circuit breaker space in the electrical panel adjacent to the circuit breaker for the branch circuit in A above and labeled with the words “Future 240V Use”; and

2.    A Category III or IV vent, or a Type B vent with straight pipe between the outside termination and the space where the water heater is installed; and

3.    A condensate drain that is no more than 2 inches higher than the base of the installed water heater, and allows natural draining without pump assistance, and

4.    A gas supply line with a capacity of at least 200,000 Btu/hr.

(b)      Water heating recirculation loops serving multiple dwelling units shall meet the requirements of Section 110.3(c)4.

(c)       Solar water-heating systems and collectors shall be certified and rated by

the Solar Rating and Certification Corporation (SRCC), the International Association of Plumbing and Mechanical Officials, Research and Testing (IAPMO R&T), or a listing agency that is approved by the Executive Director.

(d)      Instantaneous water heaters with an input rating greater than 6.8 kBTU/hr (2kW) shall meet the requirements of Section 110.3(c)6.

(e)      Commercial Boilers

1.    Combustion air positive shut-off shall be provided on all newly installed boilers as follows:

A. All boilers with an input capacity of 2.5 MMBtu/h (2,500,000 Btu/h) and above, in which the boiler is designed to operate with a nonpositive vent static pressure.

B. All boilers where one stack serves two or more boilers with a total combined input capacity per stack of 2.5 MMBtu/h (2,500,000 Btu/h).

2.    Boiler combustion air fans with motors 10 horsepower or larger shall meet one of the following for newly installed boilers:

A. The fan motor shall be driven by a variable speed drive, or

B. The fan motor shall include controls that limit the fan motor demand to no more than 30 percent of the total design wattage at 50 percent of design air volume.

3.    Newly installed boilers with an input capacity 5 MMBtu/h (5,000,000 Btu/h) and greater shall maintain excess (stack-gas) oxygen concentrations at less than or equal to 5.0 percent by volume on a dry basis over firing rates of 20 percent to 100 percent. Combustion air volume shall be controlled with respect to firing rate or flue gas oxygen concentration. Use of a common gas and combustion air control linkage or jack shaft is prohibited.

EXCEPTION to Section 160.4(e)3: Boilers with steady state full-load thermal combustion efficiency 90 percent or higher.

(f)       Insulation for Piping and Tanks

1.    Piping for multifamily domestic hot water systems, shall be insulated to meet the requirements of Table 160.4-A.

EXCEPTION 1 to Section 160.4(f)1: Factory-installed piping within space-conditioning equipment certified under Section 110.1 or 110.2..

EXCEPTION 2 to Section 160.4(f)1: Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. Piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating material to ensure that no contact is made with the metal framing. Insulation shall abut securely against all framing members.

EXCEPTION 3 to Section 160.4(f)1: Piping installed in interior or exterior walls shall not be required to have pipe insulation if all of the requirements are met for compliance with Quality Insulation Installation (QII) as specified in Reference Residential Appendix RA3.5.

EXCEPTION 4 to Section 160.4(f)1: Piping surrounded with a minimum of 1 inch of wall insulation, 2 inches of crawlspace insulation, or 4 inches of attic insulation, shall not be required to have pipe insulation.


TABLE 160.4-A PIPE INSULATION THICKNESS – Multifamily Domestic Hot Water

Fluid Operating Temperature Range (°F)

Insulation Conductivity


Nominal Pipe Diameter (in inches)

(in Btu·in/h·ft2· °F)

Mean Rating Temperature (°F)



< 1

1 to <1.5

1.5 to < 4

4 to < 8

8 and larger

Multifamily Domestic Hot Water Systems


Minimum Pipe Insulation Required
(Thickness in inches or R-value)











R 7.7

R 12.5

R 16

R 12.5

R 11

Footnote to TABLE 160.4-A:

1.     Multifamily and hotel/motel domestic hot water systems with water temperature above 140°F shall use the row in Table 120.3-A for the applicable water temperature.

2.     Insulation Protection. Pipe Insulation shall be protected from damage due to sunlight, moisture, equipment maintenance, and wind. Protection shall, at minimum, include the following:

A.     Pipe insulation exposed to weather shall be protected by a cover suitable for outdoor service.  The cover shall be water retardant and provide shielding from solar radiation that can cause degradation of the material.  Adhesive tape shall not be used to provide this protection.

B.     Pipe insulation covering chilled water piping and refrigerant suction piping located outside the conditioned space shall include, or be protected by, a Class I or Class II vapor retarder.  All penetrations and joints shall be sealed.

C.     Pipe insulation buried below grade must be installed in a waterproof and non-crushable casing or sleeve.

NOTE: Authority: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code. Reference: Sections 25007, 25008, 25218.5, 25310, 25402, 25402.1, 25402.4, 25402.5, 25402.8, and 25943, Public Resources Code.