[VAC] Re: Radiant flooring

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

There are multiple choices for radiant flooring. Heat source can be
water or electricity (look through Fine Homebuilding for advertisements
from both camps), and that heat source can be in or under the flooring.
The heat source should not be under a composite floor with foam or
honeycomb in the middle because they are both effective insulators. So
the heat source should be IN such an insulated floor just below the top
surface. Aluminum spreaders would be good, but would interfere with the
structural requirements of bonding the top surface skin to the spacing
foam/balsa/honeycomb. Or at least add another glue layer to the process.
Aluminum heat spreaders would be appropriate for an installation under a
solid wood floor.

There are multiple techniques to achieve the insulated sandwich and they
all work and have all been used for some product.

I suspect the foam filled boat hulls are most probably made by spraying
fiberglass onto a mold for the interior and into a mold for the outer
hull, fitting them together and filling the gap with foam that rises in
place. This can be done with flat sheets for the skins, so long as the
skins are supported at the desired spacing while the foam expands and
cures. Some insulated house wall/roof panels are made that way in
factories.

For very small quantity flat surfaces its as effective to use a foam
compatible adhesive such as water based contact cement to glue surface
sheets to Dow blue board. Passageways for tube or electric wire can be
cut with a loop of hot wire. Some aircraft designs use foam blocks
shaped with straight hot wires and then covered with fiberglass (or
carbon fiber or kevlar) fabric which is encased in epoxy or polyester.

Honeycomb is harder to cut to a wing airfoil but can and has been, and
it has some bending capabilities for making curved surfaces such as
parabolic radar type antennas. Gluing it takes a good epoxy generally.

The Aircraft Spruce Company http://www.aircraft-spruce.com/ catalog
describes these techniques and includes suitable raw materials.

Insulation is inherent in the design of radiant floor heating schemes.
Generally a shiny layer is desired just under the radiant heater and
spread assemble under the floor, then regular foam or fiberglass
insulation under that.

Water in tubing presents a problem of winterizing. All the water has to
come out or be replaced with antifreeze. Its normal in a house to run
the tubing front to back in a flat maze. That won't drain by gravity
very well. Since the on demand water heaters may be a bit big for the
heat load needed, it may be handier to use electric radiant heating
wires that are more easily zoned and don't need winterizing.

Gerald J.