224.0 V – — 2025 California Mechanical Code

Vacuum. A pressure less than that exerted by the atmosphere. Valve, Pressure-Relief. A pressure-actuated valve held closed by a spring or other means and designed to automatically relieve pressure in excess of its setting. Valve, Stop. A device in a piping system to shut off the flow of the fluid.

Valve, Three-Way-Type Stop. A manually operated valve with one inlet that alternately can stop flow to either of two outlets.

Valves, Companion or Block. Pairs of mating stop valves valving off sections of refrigeration systems and arranged so that these sections may be joined before opening these valves or separated after closing them.

Vent. A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Vent, Type B Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved appliances equipped to burn only gas. Vent, Type B-W Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved gas-fired vented wall furnaces. Vent, Type L Gas. A venting system consisting of listed vent piping and fittings for use with oil-burning appliances listed for use with Type L or with listed gas appliances. Vent, Gas. A passageway composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions for conveying vent gases from appliances or their vent connectors to the outdoors. [NFPA 54:3.3.53] Vent Connector, Gas. That portion of a gas-venting system that connects a listed gas appliance beginning at the draft hood or flue collar to a gas vent and is installed entirely within the space or area in which the appliance is located. Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe. [NFPA 54:3.3.101] Vented Appliance Categories. Category I. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

[NFPA 54:3.3.4.10.1] Category II. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent. [NFPA 54:3.3.4.10.2] Category III. An appliance that operates with a positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

[NFPA 54:3.3.4.10.3] Category IV. An appliance that operates with a positive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent.

[NFPA 54:3.3.4.10.4] Vented Decorative Appliance. A vented appliance whose only function is providing an aesthetic effect of flames. Vented Wall Furnace. A self-contained, vented, fuel gasburning appliance complete with grilles or equivalent, designed for incorporation in or permanent attachment to the structure of a building and furnishing heated air, circulated by gravity or by a fan, directly into the space to be heated through openings in the casing. [NFPA 54:3.3.45.7] Ventilating Ceiling. A suspended ceiling containing many small apertures through which air, at low pressure, is forced downward from an overhead plenum dimensioned by the concealed space between the suspended ceiling and the floor or roof above.

Ventilation System. All of that equipment intended or installed for the purpose of supplying air to or removing air from, any room or space by mechanical means, other than equipment that is a portion of an environmental heating, cooling, absorption, or evaporative cooling system. Venting Collar. The outlet opening of an appliance provided for connection of the vent system. Venting System. The vent or chimney and its connectors, assembled to form a continuous open passageway from an appliance to the outdoors for the purpose of removing products of combustion. This definition also shall include a venting assembly that is an integral part of an appliance. Venting System, Gravity-Type. A system that depends entirely on the heat from the fuel being used to provide the energy required to vent an appliance. Venting System, Power-Type. A system that depends on a mechanical device to provide a positive draft within the venting system. Volume, Internal Gross. The volume as determined from internal dimensions of the container, with no allowance for the volume of the internal parts.