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Glossary
atmospheric venting: venting of combustion byproducts through a vertical metal pipe
or masonry chimney. Because combustion byproducts are warmer than the surround-
ing air, they rise naturally to dissipate in the atmosphere.
boiler: a self-contained gas-burning appliance for supplying steam or hot water for
heating
Btu: British thermal unit, a common measurement of energy content, equals the
amount of energy needed to raise the temperature of 1 pound of water 1 degree
Fahrenheit
chimney: one or more passageways, vertical or nearly so, for conveying flue or vent
gases to the outside atmosphere
combo heater: a single gas appliance that provides forced-air space-heating and hot
water
CSST: corrugated stainless steel tubing, a flexible piping used instead of rigid black
pipe to distribute natural gas within a building
degree rise: the difference in temperature between the water at the beginning and
end of the heating cycle
dip-tube: the pipe that carries incoming cold water to the bottom of a water heater
tank
direct-vent: equipment designed to have all combustion gases vented through an
exterior wall. Direct vent equipment can also have a second pipe that brings air from
the outside into the combustion chamber. These units are also called "sealed combus-
tion" units.
DOE: the U.S. Department of Energy
energy factor (EF): a measurement of water heater energy efficiency based on how
efficiently the energy source heats water, the unit’s standby losses and the energy lost
as the unit cycles on and off
flue: a passage to take combustion products from a fuel-burning appliance to the out-
doors
foot-print: the area of floor space taken up by the water heater
hydronic: a term for heating systems that use circulated hot water or steam created
by a boiler
input rating: the amount of fuel energy that flows into a gas appliance over time. It is
usually measured in Btu per hour.
masonry chimney: a chimney of solid masonry units, including brick, stone or other
materials, usually lined with clay or metal flues
pilot: a small flame used to ignite the gas in the main burner of an appliance. A pilot
may be standing (constantly burning) or intermittent (on demand).
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