Onix Tubing Installation Manual

Insulation Details
Unlike a frame application where the
insulation is installed after the radiant
tubing, a slab application requires the
insulation to be installed first, making
the insulation part of the structure.
In a slab on grade application there are
two main areas to insulate: vertically
around the perimeter of the slab and
horizontally underneath the slab. Both
will aid in the slab s response and
efficiency. Of these two, the vertical
edge insulation is the most important
because it prevents heat loss directly
to the outside environment. Horizontal
insulation helps decrease the slab s
required start up time by isolating the
heating mass from the ground mass
below. Typically the system will see a
reduction of about 10% in overall
operational efficiency if a horizontal
insulation is not used.
Type of Insulation
Extruded polystyrene insulation board
is recommended mainly because the
insulation board will be in direct con-
tact with the soil. Extruded poly-
styrene insulation will not degrade
over time due to excess moisture or
soil acidity. Beaded insulation
boards should not be used because
they are not strong enough and will
break down over time. This, in turn,
will cause structural instability.
In most applications, 1" insulation
board is recommended. A thicker
board may be used if the slab is to be
installed in a cold, aggressive climate.
Always check with an architect or
structural engineer to ensure the
appropriate insulation is used.
Foil-faced insulation is not required or
recommended when insulating a radi-
ant slab. Foil-faced insulation is used
when an air gap is able to be main-
tained. In the case of a slab application
the tubing is completely encapsulated
in the concrete, eliminating any air
gap.
Watts Radiant does not recommend
Bubble-type insulation under a slab
application until more research has
been done and performance has
been verified.
Special Construction
Considerations
Slab applications are generally the eas-
iest to install. However, it is important
to remember what type of construction
steps remain after the concrete slab
has been poured. In most projects, the
concrete is the first phase of the proj-
ect. Interior walls and other supports
structures still have to be installed,
most being mounted or secured direct-
ly to the slab. With this in mind, it is
important to take some preliminary
steps to help protect the tubing during
construction.
Control Joints
Concrete slabs will expand and con-
tract due to thermal changes. To pre-
vent damage to the slab, expansion
joints are used to control this move-
ment. In some cases cut joints are used
to control where cracking is to occur.
Make sure the tubing is protected
according to the requirements of the
control joint.
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 are required. Concrete
is a very conductive material, 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 residential slabs will use 12"
tube spacing with some perimeter
banding. In a few cases, where control
over supply fluid temperature is need-
ed, an entire room may be installed at
6" on center. This may be the case in a
high heat loss sunroom or pool area.
page 36 Watts Radiant: Onix Installation Manual
Insulation
Board
Subgrade
Onix
Concrete
Rewire/Rebar
Concrete Slab