My husband (a builder) and I will soon be starting to build our house (northern NY) and I have been given the job of on-line research for various aspects of the project.  Right now I'm trying to find information on the best type of decking or underlayment for radiant heat for the main floor (there will be a full basement wtih one floor above that with the radiant heat.  Possibly no heat in the basement).  The envelope will be ICF foundation and SIPS walls/roof.  I looked at the Maxxon website (manufacturer of gypcrete) and they have a product called Thermafloor that they say is for this purpose.  I am under the impression that radiant heat is most effective when imbedded in some sort of mass (such as the slab) that holds the heat.  It seems a lot of heat will be lost if the tubing is simply applied suspended under the subfloor. Does anyone have any experience with a product such as Thermafloor?  Forgive my terminology, or lack thereof.  I am learning as fast as I can!  Thanks in advance for your assistance and I'm sorry if this information might be somewhere in the forum.  I began to try to research the forum but it is a daunting task.  

for lower water temperatures, the issue is conductivity, not mass. gypcrete is good for this, other options are aluminized panels or subfloor products.

mass adds some buffer capacity and also some control concerns, and for even heating those concerns are similar in both cases. some sort of dynamic water temperature control helps a lot.

CathyK,

 Take a look at the subject: Thermal Mass Flooring with Tubing (submitted by Alexis) . this may be of help... The benefit of gypscrete is the thermal mass to weight ratio. This will increase the "flooring Dead Load" and must be accounted for as your engineer/ design the flooring structure. This may require additional material and labor cost (oh yea you said your husband is the builder "lucky him" ).

I would recommend you think about putting Radiant heat into the basement flooring at the onset. You may want to enpand the usage of the basement in the future AND this is a way to increase your thermal mass / heat storage and reduce your overall thermal recovery rate..

Thanks. It looks like we can't get the lightweight materials up here anyway so will be using concrete with the appropriate flooring joist system. As I said, I'm learning as fast as I can.

CathyK,

 I am alos building in upsate NY. 1 hour north of Albany. Where are you building?

In the Tri-Lakes region of the Adirondacks.

oops....I should clarify.....Lake Placid/Saranac Lake/Tupper Lake region.