Definition of
Heating Terms
The definitions given in this section are only
those applying to heating and particularly as
used in this book. Some do not define the terms
for all usages.
Absolute Humidity:
The weight of water vapor in
grains actually contained in one cubic foot of the
mixture of air and moisture.
Absolute Pressure:
The actual pressure above
zero. It is the atmospheric pressure added to the
gauge pressure. It is expressed as a unit pres-
sure such as Ibs.per sq. in. absolute.
Absolute Temperature:
The temperature of a
substance measured above absolute zero. To
express a temperature as absolute temperature
add 460° to the reading of a Fahrenheit ther-
mometer or 273° to the reading of a Centigrade.
Absolute Zero:
The temperature (-460°F.
approx.) at which all molecular motion of a sub-
stance ceases, and at which the substance con-
tains no heat.
Air:
An elastic gas. It is a mechanical mixture of
oxygen and nitrogen and slight traces of other
gases. It may also contain moisture known as
humidity. Dry air weighs 0.075 Ibs. per cu. ft.
One Btu will raise the temperature of 55 cu. ft.
of air one degree F.
Air expands or contracts approximately 1/490 of
its volume for each degree of rise or fall in tem-
perature from 32° F.
Air Change:
The number of times in an hour the
air in a room is changed either by mechanical
means or by the infiltration of outside air leaking
into the room through cracks around doors and
windows, etc.
Air Cleaner:
A device designed for the purpose
of removing air-borne impurities such as dust,
fumes, and smokes. (Air cleaners include air
washers and air filters.)
Air Conditioning:
The simultaneous control of
the temperature, humidity, air motion, and air
distribution within an enclosure. When human
comfort and health are involved, a reasonable
air purity with regard to dust, bacteria,and odors
is also included. The primary requirement of a
good air conditioning system is a good heating
system.
Air Infiltration:
The leakage of air into a house
through cracks and crevices, doors, windows,
and other openings, caused by wind pressure
and/or temperature difference.
Air Valve:
See Vent Valve.
Atmospheric Pressure:
The weight of a column
of air, one square inch in cross section and
extending from the earth to the upper level of
the blanket of air surrounding the earth. This air
exerts a pressure of 14.7 pounds per square
inch at sea level, where water will boil at 212°F.
High altitudes have lower atmospheric pressure
with correspondingly lower boiling point tempera-
tures.
Boiler:
A closed vessel in which steam is gener-
ated or in which water is heated by fire.
Boiler Heating Surface:
The area of the heat
transmitting surfaces in contact with the water
(or steam) in the boiler on one side and the fire
or hot gases on the other.
Boiler Horsepower:
The equivalent evaporation
of 34.5 Ibs. of water per hour at 212° F. to
steam at 212° F. This is equal to a heat output
of 33,475 Btu per hour, which is equal to
approximately 140 sq. ft. of steam radiation
(EDR) .
British Thermal Unit (Btu):
The quantity of heat
required to raise the temperature of 1 Ib. of
water 1°F. This is somewhat approximate but
sufficiently accurate for any work discussed in
this book.
Bucket Trap (Inverted):
A float trap with an
open float. The float or bucket is open at the
bottom. When the air or steam in the bucket has
been replaced by condensate the bucket loses
its buoyancy and when it sinks it opens a valve
to permit condensate to be pushed into the
return.
Bucket Trap (Open):
The bucket (float) is open
at the top. Water surrounding the bucket keeps
it floating and the pin is pressed against its
seat. Condensate from the system drains into
the bucket. When enough has drained into it so
that the bucket loses its buoyancy it sinks and
pulls the pin off its seat and steam pressure
forces the condensate out of the trap.
Calorie (Small):
The quantity of heat required to
raise 1 gram of water 1°C (approx.).
Calorie (Large):
The quantity of heat required to
raise 1 kilogram of water 1°C (approx.).
Centigrade:
A thermometer scale at which the
freezing point of water is 0° and its boiling is
100°.
Central Fan System:
A mechanical indirect sys-
tem of heating, ventilating, or air conditioning
consisting of a central plant where the air is
heated and/or conditioned and then circulated
by fans or blowers through a system of distribut-
ing ducts.
Chimney Effect:
The tendency in a duct or other
vertical air passage for air to rise when heated
due to its decrease in density.
46
Chapter 6
