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How To Calculate KW Rating Required
We arrive at the required output by dividing the volume (cubic metres) by 11.4. This gives the
approximate kilowatt requirement to maintain an insulated space to 20ºc when it is 1ºc outside.
A room measuring 5m x 6m x 2.4m high = 72m³ Divide By 11.4 = 6.3 kw so a 6kw stove standing proud in the room
would be quite adequate.
However, if the stove is going in a recess or alcove (we’d usually recommend an opening of at least
800mm square), presume up to a third of the radiant heat will be absorbed in the recess, so an 8kw stove would
be required. If the chimney is fairly central in the house, and the stove will be in regular use over the winter,
using the recess as a 'heat-sink' could actually be an advantage.
The same heating calculation works for a whole house. If the stove incorporates a boiler, approximately
20% of heat is in the pipe work, and 3kw should be allowed for the hot water cylinder (this is heated by 'gravity'
or thermal convection, while the radiators are fed by an electric pump, which is thermostated from the hot water
cylinder – so the pump comes on automatically when the cylinder is properly warm; if a hot water cylinder is not on
the system, a heat leak radiator must be installed, in case of pump failure).
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