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47
Convectors
There are two types of convector: natural and fan.
Natural convectors rely on gravity convection currents produced by the
heater. Skirting heaters have a finned pipe inside a sheet metal casing. Their
heat emission is about 480 W per metre run, they are light and easily handled
and they are less obtrusive than taller equipment. They are always fitted onto
two-pipe systems and the return pipe can be fitted inside the casing. Valves and
air vents are enclosed in accessible boxes at the ends of continuous lengths.
Natural convectors produce a uniformly rising current of warm air around the
perimeter of the room and this is effective in producing a comfortable environ-
ment. There is negligible radiant heating. Other natural convectors are either 1
m high or extend up to room height. They create strong convection currents
with little radiation and are particularly suitable for locations where elderly,
very young or disabled people are being cared for as there are no hot surfaces
that may cause skin burns or start fires. Natural convectors have high heat out-
puts and can be built into walls, cupboards or adjacent rooms to improve their
appearance. Electricity or low- or medium-temperature hot water can be used as
the heating medium. The heating elements need periodic cleaning. Such heaters
are used in locations where quiet operation and the lack of draughts or intense
radiation are important design considerations, such as libraries, art galleries and
antique furniture stores.
Fan convectors have a construction similar to natural convectors with the
addition of one or more centrifugal fans and an air filter. Heat output can be
very high and fans may be operated at various fixed speeds or from variable-
speed motors. Fan operation is controlled from built-in thermostats or remote
temperature sensors.
Installation can be at low or high level and the heated air stream is di-
rected away from sedentary occupants. Fan convectors can be usefully sited at
doorways to oppose incoming cold air and rapidly reheat entrance areas.
A two-pipe circuit must be used, and fan convectors are installed on sepa-
rate circuits from hot-water radiators as their control characteristics are different.
Constant-temperature hot-water is supplied to them, whereas radiators
may have variable water temperatures to reduce heat output in mild weather.
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