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Heating systems may be classified as
central or local.
Central heating is often used in cold
climates to heat private houses and public
buildings. Such a system contains a
boiler,
furnace, or
heat pump to heat water, steam, or air, all
in a central location such as a
furnace room in a home or a
mechanical room in a large building. The
system also contains piping or ductwork to
distribute the heated fluid, and
radiators to transfer this heat to the air.
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The term radiator in this context is
misleading since most heat transfer from the
heat exchanger is by
convection, not
radiation. The radiators may be mounted on
walls or buried in the floor to give under-floor
heat.
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In boiler fed or radiant heating systems, all
but the simplest systems have a pump to
circulate the water and ensure an equal supply
of heat to all the radiators. The heated water
can also be fed through another heat exchanger
inside a storage cylinder to provide hot running
water.
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Forced air systems send heated air through
ductwork. During warm weather the same
ductwork can be reused for air conditioning. The
forced air can also be filtered or put through
air cleaners. Most ducts cannot fit a human
being (as they do in many films) since this
would require a greater duct-structural
integrity and create a potential security
liability.
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Heating can also be provided from electric,
or resistance heating using a filament that
glows hot when you cause electricity to pass
through it. This type of heat can be found in
electric baseboard heaters, portable electric
heaters, and as backup or supplemental heating
for heat pump (or reverse heating) system.
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The heating elements (radiators or vents)
should be located in the coldest part of the
room and typically next to the windows to
minimize condensation. Popular retail devices
that direct vents away from windows to prevent
"wasted" heat defeat this design parameter.
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Drafts contribute more to the subjective feeling
of coldness than actual room temperature.
Therefore, rather than improving the heating of
a room/building, it is often more important to
control the air leaks.
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The invention of central heating is often
credited to the
ancient Romans, who installed a system of
air ducts called "hypocaust"
in the walls and floors of public baths and
private villas. The ducts were fed with hot air
from a central fire. Generally, these heated by
radiation; a better physiologic approach to
heating than conventional forced air convective
heating.
