Onix Tubing Installation Manual

Watts Radiant: Onix Installation Manual page 43
Thin Slab
and Slab Cap
Applications
Some construction details call for a
Thin Slab, or a lightweight concrete,
to be applied above the subfloor.
These applications offer increased
sound quality to a room and an
increased thermal mass to the radiant
heating system. In some cases, thin
slabs are used to act as a fire-stop
from floor to floor.
Most Thin Slab applications are
installed during the initial construction
of a building, due to the increased
structural requirements to carry the
added weight.
Most lightweight concrete products
will increase the floor height by 1.5"
and the floor load anywhere from 12
to 18 lbs./sq.ft. This increase in load
usually means a modification to the
joist system and/or other support
modifications. It is important to verify
a floor s ability to withstand these
loads prior to installing a lightweight
concrete product.
Design Parameters
For proper radiant design it is impor-
tant know the type of layers used in
the floor construction. As these layers
increase or change, variances in the
heating system result. Portland and
gypsum based concrete are very con-
ductive materials, allowing for a wider
spread in heat transfer throughout the
mass. However, certain limitations
should be present to ensure certain
comfort levels are maintained.
Onix Spacing
Most thin slabs will use 12" tube spac-
ing with some perimeter banding. In a
few cases, where control over supply
fluid temperature is needed, an entire
room may be installed at 9"or 6" cen-
ters. This may be the case in a high
heat loss sunroom or pool area.
In a Thin Slab over Frame Floor appli-
cation, Onix is generally installed
directly to the subfloor with the use of
staples and/or NailTites. If the thin
slab is to be installed over an existing
slab, tube talons may be used to secure
the Onix.
Closer spacing may be used in areas of
high heat loss, such as an exposed wall
with a high percentage of glass; 9" o.c.
spacing is sometimes preferred in
bathrooms, kitchens and entries.
Closer tube spacing, up to 6 inches on
center, may also be used in areas that
have a low thermal conductivity, such
as areas with dense floor coverings
such as a carpet and pad.
It is important to note that simply dou-
bling the amount of tubing does not
double the floor s heating output. The
floor s ability to deliver heat to a room
is based on its surface temperature.
The radiant tubing controls this sur-
face temperature. More tubing, or
tighter spacing, allows for the same
surface temperature to be reached at a
slightly lower supply fluid tempera-
ture.
Watts Radiant s RadiantWorks design
software generates a specific nomo-
graph for each room in the design.
Nomographs convey several key fac-
tors associated with a room, such as
tube spacing, floor surface tempera-
ture, floor heating intensity, mean
(average) supply water temperature
and back and edge loss values.
Nomographs are essential to any radi-
ant design. More information on how
to read and use a Nomograph can be
found in the Appendix.
Supply/Return Manifolds
Floor Covering
1
1
2
" Thin Slab
Subfloor
Onix
Joist
Insulation
Typical thin slab construction detail.
Thin Slabs