Glossary
1407
ductwork runs below the level of the furnace. Also called
counterflow furnace. (32)
draft. In a combustion heating system, the movement of flue
gas. Draft affects combustion as it allows for the supply of
oxygen for burning. (36)
draft gauge. A gauge used to measure the air pressure of the
flue in a combustion heating system. (36)
draft regulator. A device installed in a flue pipe to regulate
the amount of air drawn into the flue. A draft regulator may
be controlled thermostatically, electrically, or barometri-
cally. Also called barometric damper or vent damper. (36)
draft test. A test used to determine the rate of flue gas flow
in a combustion heating system. Draft is measured in inches
of water column (in. WC). (36)
drainback system. In a closed liquid-based solar heating
system, a system design that uses gravity to drain liquid
from the solar collectors whenever the pump is off. (39)
drift. The loss of a cooling tower’s water when it is broken
into droplets small enough to be caught in a draft and car-
ried away between the louvers. (45)
drift punch. A type of punch used to align holes in mating
surfaces so that a fastener can be inserted. (3)
dry underfloor radiant heating system. A hydronics radi-
ant heating system that consists of tubing attached to a
wood floor or subfloor. (33)
dry-base boiler. A boiler in which the area under the com-
bustion chamber is dry and the water is contained in an area
above the burner. (33)
dry-bulb temperature. The air temperature taken with the
sensitive element of the thermometer in a dry condition. (21)
dual-pressure regulator. A control valve with two pilot
pressure regulators. (16)
dual-voltage motor. A motor that has its stator windings
arranged in pairs so that it can be used with two different
voltages. Three-phase motors are typically dual-voltage
motors. (12)
duct. A channel or tube for conveying air in a heating and
cooling system. (23)
duct heater. An array of electric heating elements contained
in a single unit that can be installed in a run of ductwork. (37)
duct sweeper. A device used to release dust, mold, and mil-
dew from the sides of the ducts by rotating through the duct-
work. (24)
dust. Small particles (1–200 microns) that become tempo-
rarily airborne from wind, a sudden earth disturbance, or
mechanical work on a solid substance. (22)
eccentric. A shaft section that is larger and has a different
center than the rest of the shaft. (15)
eccentric reducer fitting. A fitting used to join tubing of dif-
ferent sizes in a hot-water hydronic system. The fitting off-
sets the centerlines of the differently sized tubes to reduce
the danger of air pockets forming. (33)
eddy currents. Small circular airflow patterns that could
disturb proper airflow in a conditioned space cabinet. (46)
effective latent heat. The amount of heat absorbed from a
conditioned space cabinet and evaporator. (48)
effective length. The length of a duct run determined by
adding the physical length of the ductwork to effective
length values for each fitting in the duct run. (23)
ejector. A device used to push ice out of its mold. (18)
elbow. A part of the duct system with a 90° bend. (23)
electric baseboard heating unit. A convection heating
unit that consists of an electric heating element in a casing
that is mounted close to the floor on a wall, usually under
windows. (37)
electric evaporator pressure regulator (EEPR). An EPR
that uses a stepper motor to proportionally modulate its
valve position in reaction to evaporator temperature. (46)
electric furnace. A furnace that consists of a central air han-
dler with electric heating elements that are used to warm
circulating air for a conditioned space. (37)
electric heat defrost. An air-source heat pump defrost
method that uses an electric resistance heater near the out-
door coil to melt ice and frost. (34)
electric heat defrost system. A defrost system in which
electric heating coils are installed in an evaporator, around
it, or within the refrigerant passages and energized to melt
ice and frost buildup. (46)
electric heating element. A conductor through which elec-
tric current is passed in order to produce heat. There are
three basic types of electric heating elements: open wire,
open ribbon, and tubular cased wire. (37)
electric interlock. A furnace safety device that prevents the
ignition control module from opening the gas valve or turn-
ing on the indoor blower until all proper operating condi-
tions are met. (35)
electric radiant heat. A system that uses heating elements
to radiate heat that primarily warms objects instead of air.
Electric radiant heat is generally classified as direct or indi-
rect. (37)
electric resistance heating. The process of producing
heat by conducting electricity across electric heating ele-
ments. (37)
electrical circuit. A path for electrons to flow from a power
source, through conductors, across a load, and back to the
power source. (9)
electricity. The flow of electrons from one atom to another. (9)
electrodeposition. A process in which metallic particles are
applied to another metal surface (conduction plate) using an
electric current. This process bonds the surface material to
the metal conduction plate. (39)
electromagnet. A magnet created by coiling a conductor
around a piece of soft iron. (9)
electromagnetism. The magnetic effect caused by current
flowing through a coil of wire. (9)
electromotive force (emf). The electrical force or electrical
pressure created by a potential difference in atomic charges
between two points. Also called voltage. (9)