Onix Tubing Installation Manual

Slab on Grade
Applications
Introduction
Slab applications are one of the most
common applications used by com-
mercial, as well as residential, radiant
heating systems. The added thermal
mass provided by a slab increases the
overall thermal efficiency of the sys-
tem, while providing more even heat
distribution throughout the structure.
However, since the slab is in direct
contact with the ground, energy can be
lost to the surroundings. To help
reduce these back and edge losses, cer-
tain conditions must be met prior to
the radiant installation to help ensure
proper system operation.
Site Preparation
A radiant slab should be placed on
well drained base rock material. Sub-
surface water will rob heat from a
radiant slab faster than a boiler can
produce it. Basements and slabs
installed in hillsides should have good
drainage to carry any subsurface
groundwater away from the site. The
slab should be placed above an ample
amount of crushed rock or gravel.
Watts Radiant: Onix Installation Manual page 35
Radiant slabs placed on low-lying,
poorly drained soil or sand should
have at least one inch of extruded
polystyrene (Dow
¤
Blue Board
¤
) insu-
lation under the entire slab - even in
southern climates.
A radiant slab should never be placed
directly on top of clay or organic sub-
soil, as these materials can conduct
heat away from the radiant slab, and
the soils may shrink in volume when
directly exposed to the heat of the
slab. An intervening layer of four or
more inches of crushed rock or river
gravel should be used.
A
radiant slab should never be placed
directly on top of solid bedrock, as this
material can rapidly conduct heat from
the slab into the earth. Crushed rock
and/or insulation must be installed
between the slab and rock.
Sometimes one to two inches of sand
is placed on top of the coarser base
rock material. This gives a smooth,
level surface to lay down rigid insula-
tion, and helps prevent possible
breakup of the rigid insulation in high
traffic areas prior to concrete place-
ment. The sand layer also allows for
more precise leveling to minimize any
variation in the slab thickness.
Supply/Return Manifold
Slab
Onix
Rewire
Base
Insulated Slab on Grade.
Concrete Slab