Water Heaters

Water Heaters

Reference text for the water heaters area. Every rule below is written from the printed line of the

2024 International Plumbing Code (IPC 2024) that carries it, and each rule names the section it comes

from. Where the printed line does not state a value, no value is stated here. The text reads the whole

of Chapter 5 of the code, together with the section that governs the hot water supply system in

Chapter 6 and the sections those two chapters refer to.

1. General

The chapter governs the materials, the design and the installation of water heaters and of the

related safety devices and appurtenances (IPC 2024, 501.1). The purpose stated by the code for the

whole chapter: the chapter carries the regulations concerning the safety of water heating units and

hot water storage tanks, because heated (hot or tempered) potable water is needed for the plumbing

fixtures associated with handwashing, bathing, culinary activities and building maintenance; heated

water is commonly stored in large pressurized tanks that must be protected against explosion by the

pressure and temperature relief valves specified in the chapter, and the chapter also covers access

to the equipment so that it can be maintained and replaced (IPC 2024, Chapter 5, About this chapter).

Where a combination system heats potable water and also serves space heating, and that system needs

water for space heating at a temperature above 140°F (60°C), a temperature-actuated mixing valve

complying with ASSE 1017 is provided, to hold the water supplied to the potable hot water

distribution system at 140°F (60°C) or less; the potability of the water is maintained throughout the

system, and the requirements for combination potable water heating and space heating systems follow

the International Mechanical Code (IPC 2024, 501.2).

Drain valves for emptying are installed at the bottom of every tank-type water heater and every hot

water storage tank; the inlet of the drain valve is not less than 3/4-inch (19 mm) nominal iron pipe

size, and its outlet carries male garden hose threads (IPC 2024, 501.3).

Water heaters and storage tanks are located and connected so that access is provided for observation,

maintenance, servicing and replacement (IPC 2024, 501.4), and water heaters are third-party

certified (IPC 2024, 501.5).

The water leaving a tankless water heater is not hotter than 140°F (60°C) where the heater is

intended for domestic uses; that rule does not displace the requirement for protective shower valves

of Section 412.3 (IPC 2024, 501.6).

Storage tanks and water heaters installed for domestic hot water carry their maximum allowable

working pressure clearly and indelibly stamped in the metal, or marked on a plate welded to the tank

or otherwise permanently attached to it; the marking is placed in a position with access on the

outside of the tank, so that inspection or reinspection is readily possible (IPC 2024, 501.7).

Hot water supply systems are equipped with automatic temperature controls able to be adjusted from

the lowest to the highest acceptable temperature setting of the intended operating range

(IPC 2024, 501.8). Water heaters that form part of the potable water distribution system comply with

NSF 372 and have a weighted average lead content of 0.25 percent or less (IPC 2024, 501.9).

2. Installation

Water heaters are installed in accordance with the manufacturer's instructions. Beyond that, the code

divides the equipment by the fuel or the energy source it uses: oil-fired water heaters conform to

this code and to the International Mechanical Code; electric water heaters conform to this code and

to NFPA 70; gas-fired water heaters conform to the International Fuel Gas Code; and solar thermal

water heating systems conform to the International Mechanical Code and to ICC 900/SRCC 300

(IPC 2024, 502.1). The elevation of the ignition sources of a water heater, and the protection of the

water heater against mechanical damage, follow the International Mechanical Code and the

International Fuel Gas Code (IPC 2024, 502.1.1).

A water heater that uses solid, liquid or gas fuel is not installed in a room that contains

air-handling machinery where that room is used as a plenum (IPC 2024, 502.2).

Where a water heater is installed in an attic, the attic is provided with an opening and an

unobstructed passageway large enough to allow the water heater to be removed. The printed dimensions

are: the passageway is not less than 30 inches (762 mm) in height and 22 inches (559 mm) in width,

and not more than 20 feet (6096 mm) in length measured along the centreline of the passageway from

the opening to the water heater; the flooring of the passageway is continuous and solid, and not

narrower than 24 inches (610 mm); at the front, or at the service side, of the water heater a level

space is kept for servicing, 30 inches (762 mm) in length and 30 inches (762 mm) in width; and the

clear access opening is not smaller than 20 inches by 30 inches (508 mm by 762 mm) where those

dimensions are large enough to allow the removal of the water heater (IPC 2024, 502.3).

Where earthquake loads apply in accordance with the International Building Code, water heater

supports are designed and installed for those seismic forces (IPC 2024, 502.4).

Appliances are provided with access for inspection, service, repair and replacement without disabling

the function of a fire-resistance-rated assembly and without removing permanent construction, other

appliances, or piping or ducts that are not connected to the appliance being worked on; a level

working space not less than 30 inches (762 mm) in length and 30 inches (762 mm) in width is provided

in front of the control side for servicing (IPC 2024, 502.5).

3. Connections

The cold water branch line that runs from the main water supply line to each hot water storage tank

or water heater is provided with a valve located near the equipment and serving only that tank or

heater. That valve does not interfere with, and does not cause a disruption of, the cold water supply

to the remainder of the cold water system, and it is provided with access on the same floor level as

the water heater it serves (IPC 2024, 503.1).

The method by which a circulating water heater is connected to the tank must provide proper

circulation of water through the water heater, and the pipe or tubing installed for appliances that

draw from the water heater or the storage tank complies with the code provisions for material and

installation (IPC 2024, 503.2).

4. Safety devices

4.1 Antisiphon devices

An approved means must be provided to prevent the siphoning of any storage water heater or storage

tank. The print names two acceptable means: a dip tube in the cold water line, pierced by a hole at

its top, or a valve that opens against vacuum, installed in the cold water supply above the top of

the heater or the tank (IPC 2024, 504.1).

4.2 Vacuum relief valve

Bottom fed water heaters, and bottom fed tanks connected to water heaters, have a vacuum relief valve

installed, and that valve complies with ANSI Z21.22 (IPC 2024, 504.2).

4.3 Shutdown

An electric hot water supply system is provided with a means of disconnecting it from its energy

supply in accordance with NFPA 70. Every other type of hot water supply system is provided with a

separate valve to shut off the energy fuel supply (IPC 2024, 504.3).

4.4 Relief valve

Storage water heaters that operate above atmospheric pressure are provided with an approved,

self-closing (levered) pressure relief valve and temperature relief valve, or a combination of the

two, and the relief valve complies with ANSI Z21.22. The relief valve must not be used as a means of

controlling thermal expansion (IPC 2024, 504.4).

The valves are installed in the shell of the water heater tank, and a temperature relief valve is

located in the tank so that it is actuated by the water in the top 6 inches (152 mm) of the tank

served. Where the installation has separate storage tanks, the approved, self-closing (levered)

pressure relief valve and temperature relief valve, or the combination of them, conforming to

ANSI Z21.22, is installed on both the storage water heater and the storage tank. No check valve and

no shutoff valve is placed between a relief valve and the heater or the tank it serves

(IPC 2024, 504.4.1).

4.5 Relief valve approval and settings

Temperature and pressure relief valves, combinations of them, and energy cutoff devices bear the

label of an approved agency. Their temperature setting is not more than 210°F (99°C), and their

pressure setting does not exceed the rated working pressure of the tank or water heater manufacturer,

or 150 psi (1035 kPa), whichever is less. The relieving capacity of each pressure relief valve and of

each temperature relief valve is equal to, or greater than, the heat input to the water heater or the

storage tank (IPC 2024, 504.5).

4.6 Requirements for discharge piping

The discharge piping that serves a pressure relief valve, a temperature relief valve, or a

combination of them, satisfies fourteen printed requirements (IPC 2024, 504.6):

to the air gap.

equipment.

receptor or to the outdoors.

pipe diameter above, the floor or the flood level rim of the waste receptor.

approved for such use in accordance with ASME A112.4.1.

larger than the size of the relief valve outlet, and the outlet end of such tubing is fastened in

place.

4.7 Required pan

Where a storage tank-type water heater or a hot water storage tank is installed in a location where

water leaking from the tank would cause damage, the tank is installed in a pan built of one of the

following: galvanized steel or aluminium not less than 0.0236 inch (0.6010 mm) in thickness; plastic

not less than 0.036 inch (0.9 mm) in thickness; or other approved materials (IPC 2024, 504.7). A

plastic pan installed beneath a gas-fired water heater is built of a material that has a flame spread

index of 25 or less and a smoke-developed index of 450 or less when tested in accordance with

ASTM E84 or UL723, and water heaters installed in pans comply with Section 314.2.3.2

(IPC 2024, 504.7).

The pan is not less than 1 1/2 inches (38 mm) in depth and is of sufficient size and shape to receive

all dripping or condensate from the tank or the water heater. It is drained by an indirect waste pipe

with a diameter of not less than 3/4 inch (19 mm), and the piping for safety pan drains is of the

materials listed in Table 605.4 (IPC 2024, 504.7.1).

The pan drain keeps its full size. It ends either over a suitably located indirect waste receptor or

floor drain, or outside the building, where it stops above the adjacent ground surface at 6 inches

(152 mm) or more but not more than 24 inches (610 mm). A replacement water heater installation does

not require a pan drain where none was installed before (IPC 2024, 504.7.2).

5. Insulation

Unfired hot water storage tanks are insulated to R-12.5 (h × ft² × °F)/Btu (R-2.2 m² × K/W)

(IPC 2024, 505.1).

6. Hot water supply system

6.1 Where hot water is required

In residential occupancies, hot water is supplied to the plumbing fixtures and equipment used for

bathing, washing, culinary purposes, cleansing, laundry or building maintenance. In nonresidential

occupancies, hot water is supplied for culinary purposes, cleansing, laundry or building maintenance

purposes, and hot water or tempered water is supplied for bathing and washing purposes

(IPC 2024, 607.1).

A thermostat control on a water heater serves as the temperature limiting means, for the purpose of

complying with the maximum allowable hot or tempered water delivery temperature at fixtures, only

where the water heater complies with ASSE 1082 or ASSE 1085 (IPC 2024, 607.1.1).

Tempered water is controlled by one of four printed means: a limiting device conforming to

ASSE 1070/ASME A112.1070/CSA B125.70 and set to not greater than 110°F (43°C); a thermostatic mixing

valve conforming to ASSE 1017; a water heater conforming to ASSE 1082; or a water heater conforming

to ASSE 1084. That provision does not displace the requirement for protective shower valves of

Section 412.3 (IPC 2024, 607.1.2).

6.2 Distance from the source to the fixtures

The developed length of the hot or tempered water piping, measured from the source of hot water to

the fixtures that require hot or tempered water, is not more than 50 feet (15 240 mm); recirculating

system piping and heat-traced piping count as sources of hot or tempered water

(IPC 2024, 607.2).

In occupancies required to comply with the commercial provisions of the International Energy

Conservation Code, the developed length of hot or tempered water piping is limited in accordance with

that code (IPC 2024, 607.2.1).

6.3 Circulation and heat trace

Where the occupancy falls in Group R2, R3 or R4 and stands three stories or less in height above

grade plane, the heated water circulation and temperature maintenance systems are installed under the

residential provisions of the International Energy Conservation Code; every other occupancy installs

its circulation and heat trace systems under the commercial provisions of that code

(IPC 2024, 607.2.2).

The controls on pumps that circulate water between a water heater and a storage tank for heated water

limit the operation of the pump from the start of a heating cycle to not greater than 5 minutes after

the end of that cycle (IPC 2024, 607.2.2.1).

A water distribution system that has one or more recirculation pumps moving water from a heated water

supply pipe back to the heated water source through a cold water supply pipe is a demand recirculation

water system. The pumps have controls that satisfy both of two printed conditions: the control starts

the pump on a signal from the action of a user of a fixture or appliance, on sensing the presence of a

user of a fixture, or on sensing the flow of hot or tempered water to a fixture fitting or appliance;

and the control limits the temperature of the water entering the cold water piping to 104°F (40°C)

(IPC 2024, 607.2.2.2).

Where a temperature-actuated mixing valve is used in a system that has a hot water recirculating pump,

the hot water or tempered water return line is routed to the cold water inlet pipe of the water

heater and to the cold water inlet pipe or the hot water return connection of the temperature-actuated

mixing valve (IPC 2024, 607.2.3).

6.4 Thermal expansion control

Where a storage water heater is supplied with cold water that passes through a check valve, a pressure

reducing valve or a backflow preventer, a thermal expansion control device is connected to the water

heater cold water supply pipe at a point downstream of all of those check valves, pressure reducing

valves and backflow preventers. Thermal expansion tanks are sized in accordance with the tank

manufacturer's instructions, and the sizing is such that the pressure in the water distribution system

does not exceed the pressure required by Section 604.8 (IPC 2024, 607.3).

6.5 Flow of hot water to fixtures

Fixture fittings, faucets and diverters are installed and adjusted so that the flow of hot water from

the fitting corresponds to the left-hand side of the fixture fitting (IPC 2024, 607.4). That rule

yields to one printed exception: a shower or tub/shower mixing valve that conforms to

ASSE 1016/ASME A112.1016/CSA B125.16 or to ASME A112.18.1/CSA B125.1, and whose hot-water side is the

one the device carries in its own marking (IPC 2024, 607.4 and Exception).

6.6 Insulation of piping

Where the occupancy is other than Group R2, R3 or R4 three stories or less in height above grade

plane, piping to the inlet of a water heater and piping conveying water heated by a water heater are

insulated in accordance with the commercial provisions of the International Energy Conservation Code;

for Group R2, R3 and R4 occupancies that are three stories or less in height above grade plane, the

same piping is insulated in accordance with the residential provisions of that code

(IPC 2024, 607.5).

7. Where the chapter meets the rest of the code

Chapter 5 borrows from the other codes by printed reference, and those references fix the split of

responsibility between the plumbing code and the mechanical, fuel gas, electrical and energy codes:

oil-fired, solar thermal and combination water heating under the International Mechanical Code

(IPC 2024, 501.2 and 502.1), electric water heaters under NFPA 70 (IPC 2024, 502.1 and 504.3),

gas-fired water heaters under the International Fuel Gas Code (IPC 2024, 502.1), gas-fired ignition

sources and mechanical damage protection under the mechanical and fuel gas codes (IPC 2024, 502.1.1),

and seismic support under the International Building Code (IPC 2024, 502.4).

Inside the plumbing code itself, the discharge piping of a relief valve takes the materials of

Section 605.4, where hot water distribution pipe and tubing has a printed pressure rating of not less

than 100 psi (690 kPa) at 180°F (82°C) and conforms to NSF 61 (IPC 2024, 605.4); a water heater

installed in a pan meets Section 314.2.3.2 (IPC 2024, 504.7); the protective shower valves of

Section 412.3 are not displaced by the tankless water heater temperature limit or by the tempered

water controls (IPC 2024, 501.6 and 607.1.2); and the thermal expansion control device of

Section 607.3 works against the pressure-reducing requirement of Section 604.8, which applies where

the pressure within a building exceeds 80 psi (552 kPa) static (IPC 2024, 604.8).