Radiant tubing can be installed under an existing floor with staples, by drilling holes
across the floor joists, or by just about any means the installer can design to place the
tubing as close to the bottom of the sub floor as possible. Foil faced fiberglass insulation
should be positioned with a 2" air gap between the foil and the bottom of the sub floor.
On Top of Insulated Deck
The insulation under the deck must have a 2" air space between the top of the insulation
and the bottom of the sub floor. Wood spacers the same thickness of the tubing should support
the floor over the tubing; the radiant works best if it is touching the bottom of the floor
that is over it.
On Top Of Uninsulated Deck
If the existing floor is not insulated and no access exists to do so, sleepers must be
placed on top of the floor to create a gap deep enough to place rigid insulation between
them that will carry the radiant tubing on top in such a fashion that it will touch the
underside of the upper floor.
When tubing is installed between sleepers, a masonry filler will increase the thermal mass
of the floor as well as act as a sound dampener. Do not fill the space around the tubing
with products such as vermiculite or perlite, or any Styrofoam filler that can act as an