General Underfl Oor Heating Guide - Rehau STAR 20 Installation Manuallines

GENERAL UNDERFLOOR HEATING GUIDE
Design Limits
BS EN 1264-2:1997 states that fl oors may be raised to a maximum
of 29°C and up to 35°C in peripheral areas. For screeded fl oors with
maximum design surface temperature of 29°C, the fl oor could emit
100W/m 2 with an indoor temperature of 21°C.
Pipe Spacing
Based on many years of design experience, REHAU established that
pipes should generally be spaced at 200mm centres to achieve
optimum working effi ciency. In areas of high heat loss, the pipe
spacing may be decreased to 150mm.
This is a guide only and REHAU would recommend a system design.
Screed Thickness
For solid fl oor construction, a normal fl oor screed can be used. No
special additives in the screed are required. Where the pipe is laid on
insulation, the minimum screed depth must be 65mm for domestic
applications and 75mm for commercial applications as specifi ed in UK
Building Regulations. Where heavier fl oor loadings are required, the
construction engineer should advise on the screed thickness. Where
special screeds are specifi ed, the manufacturer must be consulted
as to the screed thickness.
Floor Coverings
REHAU must be notifi ed of the fl oor covering type before design
commences.
While fl oor coverings laid above the UFH system do not normally
present problems, they must be taken into consideration at the design
stage to ensure that a good design is established. After installation,
the UFH system can be "tuned" to match the variations in fl oor
coverings from room to room by adjusting the Lockshield valves for
the individual loops.
Timber Floor Surfaces
Careful consideration of the type of fl oor to be laid must be
established before the system is designed and installed. Particular
attention should be paid to moisture content of the wooden fl oor.
Consider if the timber fl oor will be fl oated on a screed or fi xed to
battens. This will determine which type of UFH system will be used.
Not all timber fl oors are suitable for UFH and advice should be sought
from the fl ooring supplier from the trade association TRADA. Details of
the British Standard BS8201 should be observed.
Glazed Areas
In most areas of a building the heat losses are relatively similar and
unless very large areas of glass are used, the pipe centres do not
need to vary. When designing the UFH system, the warmer fl ow pipe
should be positioned to run immediately next to outside walls or other
potential cold spots. This ensures a slightly higher heat output in these
areas. Extensive areas of glazing in modern developments may require
special design consideration. A closer pipe spacing of 150mm may be
chosen.
In double height rooms, e.g. barn conversions or conservatories,
the pipes may be spaced at 150mm centres. During extreme winter
conditions, supplementary heating may still be required in glazed areas
such as conservatories where the heat losses are excessively high.
Positioning the Manifolds
It is important to fi x the positions of the manifolds at the beginning of
the design process. The position of the manifolds should be as central
as possible in order to minimise the lengths of pipe tails and unequal
loop lengths. One manifold set typically serves a fl oor area up to
2
150–240m .
Optimising Loop Lengths
To allow for different loop lengths, heat outputs and different fl oor
coverings it is necessary to balance the loops on each manifold. In
summary, the fl ow in short loops serving small rooms needs throttling
relative to longer loops serving larger rooms. If the loops are not
balanced, the shortest loop would "steal" all the water fl ow from the
longest loops, resulting in reduced heating to the largest rooms.
To help achieve fl ow balance in the system, loop lengths are normally
designed to be of similar length. To avoid many short loops serving
small rooms, some areas may be linked into one operating zone,
e.g. hallways, toilets and common areas. Two or more loops may be
required to serve larger areas.
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