Page 504 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

which makes the hot air rise. This adds up to a very warm ceiling! Underfloor
heating systems, however, rely on both conduction and radiation. The heat
from the underfloor heating system conducts through the floor, warming the
floor structure, making the floor surface a large storage heater; the heat is
then released into the room as radiated heat. Around 50 to 60 per cent of the
heat emission is in the form of radiation, providing a much more comfortable
temperature at low room levels when compared to a traditional wet system
with radiators and, with the whole floor being heated, furniture positioning
no longer becomes a problem because as the furniture gains heat, it too emits
warmth.

During the design stage, the pipe coils are fixed at specific centres depending on
the heat requirement of the room and the heat emission (in watts) per metre of
pipe. The whole floor is then covered with a screed to a specific depth, creating
a large thermal storage heat emitter. The water in the pipework circulates from
and to a central manifold and the heats the floor. The heat is then released into
the room at a steady rate. Once the room has reached the desired temperature,
a room thermostat actuates a motorised head on the return manifold and closes
the circuit to the room.

Such is the nature of underfloor heating that many fuel types can be used,
some utilising environmentally friendly technology. Gas- and oil-fired boilers are
common, but also biomass fuels, solar panels and heat pumps.
Floor coverings are an important aspect of underfloor heating. Some create
a high thermal resistivity, making it difficult for the heat to permeate
them. Carpet underlay and some carpets have particularly poor thermal
transmittance, which means the heat is kept in and not released. The thermal
resistivity of carpets and floor coverings is known as their TOG rating.

20ºC
80% convected heat
24ºC
Radiator heating
Under oor heating
Hot air rises

21°C 20ºC

20% Cooler air
radiated descends Under oor pipework
heat at 35 40ºC

18 29ºC
Radiator
at 70ºC
18ºC

p Figure 7.59 The principle of underfloor heating

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