Radiant Heat Follow-Up

I posted a question regarding radiant heat and I received very good answers. One of them, the last one, was from johnsailor, who explain that to overcome the problem of the hardwood being poor conductor of heat, in a retrofit application they use the usual aluminum heat transfer plates, with an special aluminum foil scrim covering the plate assembly and then a foam insulation (blown in place expanding foam) over that. He said that they have had very good luck with this approach.

What kind of foam, closed cell or open cell?
Besides the usual aluminum heat transfer plates, what kind of special aluminum foil scrim you used?
Anybody has any opinion about johnsailor’s opinion?
What is the most efficient boiler or hot water tank?

Original posting: http://bstoner.wpengine.com/forum/archives/2010/02/retrofitting_ra.php