Boilers and Water Heaters

This chapter establishes the installation requirements for boilers, water heaters, and pool heaters, including safety controls, expansion tanks, and specific conditions for dual-purpose or attic installations.

M2001 — Boilers

M200l.l Installation. In addition to the requirements of this code, the installation of boilers shall conform to the manufacturer's instructions. The manufacturer's rating data, the name-plate and operating instructions of a permanent type shall be attached to the boiler. Boilers shall have all controls set, adjusted and tested by the installer. A complete control diagram together with complete boiler operating instructions shall be furnished by the installer. Solid- and liquid-fuel-burning boilers shall be provided with combustion air as required by Chapter 17.

M200l.l.l Standards. Oil-fired boilers and their control systems shall be listed and labeled in accordance with UL 726. Electric boilers and their control systems shall be listed in accordance with UL 834. Boilers shall be designed and constructed in accordance with the requirements of ASME CSD-l and as applicable, the ASME Boiler and Pressure Vessel Code, Sections I and IV. Gas-fired boilers shall conform to the requirements listed in Chapter 24.

M200l.l.l Standards. Oil-fired boilers and their control systems shall be listed and labeled in accordance with UL 726. Electric boilers and their control systems shall be listed in accordance with UL 834. Boilers shall be designed and constructed in accordance with the requirements of ASME CSD-l and as applicable, the ASME Boiler and Pressure Vessel Code, Sections I and IV. Gas-fired boilers shall conform to the requirements listed in Chapter 24.

M200l.2 Clearance. Boilers shall be installed in accordance with their listing and label.

M200l.3 Valves. Every boiler or modular boiler shall have a shutoff valve in the supply and return piping. For multiple boiler or multiple modular boiler installations, each boiler or modular boiler shall have individual shutoff valves in the supply and return piping.

Exception: Shutoff valves are not required in a system having a single low-pressure steam boiler.

M200l.4 Flood-resistant installation. In areas prone to flooding as established in Table R30 1.2 (1), boilers, water heaters and their control systems shall be located or installed in accordance with Section R322.1.6.

Worked example

Scenario: An architect is specifying a new residential boiler system for a client's home.

Explanation: The design must ensure the boiler's manufacturer's rating data, name-plate, and operating instructions are permanently affixed, and that the installation strictly follows the manufacturer's guidelines in addition to the code requirements.

M2002 — Operating and Safety Controls

M2002.l Safety controls. Electrical and mechanical operating and safety controls for boilers shall be listed and labeled.

M2002.2 Hot water boiler gauges. Every hot water boiler shall have a pressure gauge and a temperature gauge, or combination pressure and temperature gauge. The gauges shall indicate the temperature and pressure within the normal range of the system's operation.

M2002.3 Steam boiler gauges. Every steam boiler shall have a water-gauge glass and a pressure gauge. The pressure gauge shall indicate the pressure within the normal range of the system's operation. The gauge glass shall be installed so that the midpoint is at the normal water level.

M2002.4 Pressure-relief valve. Boilers shall be equipped with pressure-relief valves with minimum rated capacities for the equipment served. Pressure-relief valves shall be set at the maximum rating of the boiler. Discharge shall be piped to drains by gravity to within 18 inches (457 mm) of the floor or to an open receptor.

M2002.5 Boiler low-water cutoff. All steam and hot water boilers shall be protected with a low-water cutoff control. The low-water cutoffshall automatically stop the combustion operation of the appliance when the water level drops below the lowest safe water level as established by the manufacturer.

M2003 — Expansion Tanks

M2003.l General. Hot water boilers shall be provided with expansion tanks. Nonpressurized expansion tanks shall be securely fastened to the structure or boiler and supported to carry twice the weight of the tank filled with water. Provisions shall be made for draining nonpressurized tanks without emptying the system.

M2003.l.l Pressurized expansion tanks. Pressurized expansion tanks shall be consistent with the volume and capacity of the system. Tanks shall be capable of withstanding a hydrostatic test pressure of two and one-half times the allowable working pressure of the system.

M2003.l.l Pressurized expansion tanks. Pressurized expansion tanks shall be consistent with the volume and capacity of the system. Tanks shall be capable of withstanding a hydrostatic test pressure of two and one-half times the allowable working pressure of the system.

M2003.2 Minimum capacity. The minimum capacity of expansion tanks shall be determined from Table M2003.2.

Worked example

Scenario: A new hydronic heating system design includes a hot water boiler with a nonpressurized expansion tank.

Explanation: The expansion tank must be securely fastened to the structure or boiler, supported to hold twice its water-filled weight, and provisions for draining it without emptying the entire system must be included.

M2004 — Water Heaters Used for Space Heating

M2004.l General. Water heaters used to supply both potable hot water and hot water for space heating shall be installed in accordance with this chapter, Chapter 24, Chapter 28 and the manufacturer's installation instructions.

Worked example

Scenario: A homeowner wants a single water heater to provide hot water for showers and a radiant floor heating system.

Explanation: This dual-purpose water heater must be installed in accordance with Chapter 20, Chapter 24 (Gas Piping), Chapter 28 (Potable Water), and the specific instructions provided by the manufacturer.

M2005 — Water Heaters

M2005.l General. Water heaters shall be installed in accordance with the manufacturer's installation instructions and the requirements ofthis code. Water heaters installed in an atticshall conform to the requirements of Section MI305.1.3. Gas-fired water heaters shall conform to the requirements in Chapter 24. Domestic electric water heaters shall conform to UL 174 or UL 1453. Commercial electric water heaters shall conform to UL 1453. Oiled-fired water heaters shall conform to UL 732.

M2005.2 Prohibited locations. Fuel-fired water heaters shall not be installed in a room used as a storage closet. Water heaters located in a bedroom or bathroom shall be installed in a sealed enclosure so that combustion airwill not be taken from the living space. Installation of direct-vent water heaters within an enclosure is not required.

A table appears here in the adopted code. Refer to the official source for the full table.

M2005.2.1 Water heater access. Access to water heaters that are located in an attic or underfloor crawl space is permitted to be through a closet located in a sleeping room or bathroom where ventilation of those spaces is in accordance with this code.

M2005.2.1 Water heater access. Access to water heaters that are located in an attic or underfloor crawl space is permitted to be through a closet located in a sleeping room or bathroom where ventilation of those spaces is in accordance with this code.

M2005.3 Electric water heaters. Electric water heaters shall also be installed in accordance with the applicable provisions of Chapters 34 through 43.

M2005.4 Supplemental water-heating devices. Potable water heating devices that use refrigerant-to-water heat exchangers shall be approved and installed in accordance with the manufacturer's installation instructions.

Worked example

Scenario: A design places a new water heater in the accessible attic space of a single-family dwelling.

Explanation: In addition to manufacturer's instructions and general code requirements, the water heater installation in the attic must specifically conform to the requirements outlined in Section M1305.1.3, which typically addresses access, drainage, and safety in such locations.

M2006 — Pool Heaters

M2006.1 General. Pool and spa heaters shall be installed in accordance with the manufacturer's installation instructions. Oil-fired pool heaters shall be tested in accordance with UL 726. Electric pool and spa heaters shall be tested in accordance UL 1261.

M2006.2 Clearances. In no case shall the clearances interfere with combustion air, draft hood or flue terminal relief, or accessibility for servicing.

M2006.3 Temperature-limiting devices. Pool heaters shall have temperature-relief valves.

M2006.4 Bypass valves. Where an integral bypass system is not provided as a part ofthe pool heater, a bypass line and valve shall be installed between the inlet and outlet piping for use in adjusting the flow of water through the heater.

Frequently asked questions

What are the general installation guidelines for residential boilers?

Boilers must be installed according to the manufacturer's instructions, and their rating data, name-plate, and operating instructions must be permanently attached to the unit.

Are there special rules for water heaters that supply both domestic hot water and space heating?

Yes, such water heaters must comply with this chapter, Chapter 24 (Gas Piping), Chapter 28 (Potable Water), and the manufacturer's installation instructions.

What are the requirements for installing an expansion tank with a hot water boiler?

Expansion tanks for hot water boilers must be provided. Nonpressurized tanks need to be securely fastened to the structure or boiler, supported to carry twice their water-filled weight, and allow draining without emptying the entire system.