Page 29 - 2018_IMC

DEFINITIONS

COOKING APPLIANCE. See “Commercial cooking appli- Type II. Those systems using Class II combustible liquid
ances.” solvents having a flash point at or above 100ºF (38ºC) and
DAMPER. A manually or automatically controlled device to below 140ºF (60ºC).
regulate draft or the rate of flow of air or combustion gases. Type III. Those systems using Class III combustible liq-
Volume damper. A device that, where installed, will uid solvents having a flash point at or above 140ºF (60ºC).
restrict, retard or direct the flow of air in a duct, or the Types IV and V. Those systems using Class IV nonflam-
products of combustion in a heat-producing appliance, its mable liquid solvents.
vent connector, vent or chimney therefrom.
DUCT. A tube or conduit utilized for conveying air. The air
[BS] DESIGN FLOOD ELEVATION. The elevation of the passages of self-contained systems are not to be construed as
“design flood,” including wave height, relative to the datum air ducts.
specified on the community’s legally designated flood hazard
area map. In areas designated as Zone AO, the design flood DUCT FURNACE. A warm-air furnace normally installed
elevation shall be the elevation of the highest existing grade in an air distribution duct to supply warm air for heating. This
of the building’s perimeter plus the depth number, in feet, definition shall apply only to a warm-air heating appliance
specified on the flood hazard map. In areas designated as that, for air circulation, depends on a blower not furnished as
Zone AO where a depth number is not specified on the map, part of the furnace.
the depth number shall be taken as being equal to 2 feet (610 DUCT SYSTEM. A continuous passageway for the trans-
mm).
mission of air that, in addition to ducts, includes duct fittings,
DESIGN WORKING PRESSURE. The maximum allow- dampers, plenums, fans and accessory air-handling equip-
able working pressure for which a specific part of a system is ment and appliances.
designed.
DUCTLESS MINI-SPLIT SYSTEM. A heating and cool-
DIRECT REFRIGERATION SYSTEM. A system in ing system that is comprised of one or multiple indoor evapo-
which the evaporator or condenser of the refrigerating system rator/air-handling units and an outdoor condensing unit that is
is in direct contact with the air or other substances to be connected by refrigerant piping and electrical wiring. A duct-
cooled or heated. less mini-split system is capable of cooling or heating one or
DIRECT SOLAR SYSTEM. A solar thermal system in more rooms without the use of a traditional ductwork system.
which the gas or liquid in the solar collector loop is not sepa- [BG] DWELLING. A building or portion thereof that con-
rated from the load. tains not more than two dwelling units.
[FG] DIRECT-VENT APPLIANCES. Appliances that are [A] DWELLING UNIT. A single unit providing complete,
constructed and installed so that all air for combustion is independent living facilities for one or more persons, includ-
derived from the outdoor atmosphere and all flue gases are ing permanent provisions for living, sleeping, eating, cooking
discharged to the outdoor atmosphere.
and sanitation.
DISCRETE PRODUCT. Products that are noncontinuous,
individual, distinct pieces such as, but not limited to, electri- ELECTRIC HEATING APPLIANCE. An appliance that
produces heat energy to create a warm environment by the
cal, plumbing and mechanical products and duct straps, duct application of electric power to resistance elements, refriger-
fittings, duct registers and pipe hangers. ant compressors or dissimilar material junctions.
DRAFT. The pressure difference existing between the appli-
ance or any component part and the atmosphere, that causes a ENERGY RECOVERY VENTILATION SYSTEM. Sys-
continuous flow of air and products of combustion through tems that employ air-to-air heat exchangers to recover energy
the gas passages of the appliance to the atmosphere. from or reject energy to exhaust air for the purpose of pre-
heating, precooling, humidifying or dehumidifying outdoor
Induced draft. The pressure difference created by the ventilation air prior to supplying such air to a space, either
action of a fan, blower or ejector, that is located between directly or as part of an HVAC system.
the appliance and the chimney or vent termination.
ENVIRONMENTAL AIR. Air that is conveyed to or from
Natural draft. The pressure difference created by a vent occupied areas through ducts that are not part of the heating
or chimney because of its height, and the temperature dif- or air-conditioning system, such as ventilation for human
ference between the flue gases and the atmosphere.
usage, domestic kitchen range exhaust, bathroom exhaust,
DRAIN-BACK SYSTEM. A solar thermal system in which domestic clothes dryer exhaust and parking garage exhaust.
the fluid in the solar collector loop is gravity drained from the
collector into a holding tank under prescribed circumstances. EQUIPMENT. Piping, ducts, vents, control devices and
other components of systems other than appliances that are
DRIP. The container placed at a low point in a system of pip- permanently installed and integrated to provide control of
ing to collect condensate and from which the condensate is environmental conditions for buildings. This definition shall
removable. also include other systems specifically regulated in this code.
DRY CLEANING SYSTEMS. Dry cleaning plants or sys- EQUIPMENT, EXISTING. Any equipment regulated by
tems are classified as follows:
this code which was legally installed prior to the effective
Type I. Those systems using Class I flammable liquid sol- date of this code, or for which a permit to install has been
vents having a flash point below 100ºF (38ºC). issued.

12 2018 INTERNATIONAL MECHANICAL CODE 
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