Considering a "Ledger method" heating install in a 1950 ranch total remodel. I have a solar heating system set up as the primary heat and want to run my heating water at a lower temp to utilize the solar more efficiently, which leads me to want to use the Ledger method, http://www.radiantcompany.com/details/ledger.shtml. The house has 2x10 floor joists on 16" oc spanning 11'. Does any one know if the floor could handle a 2" or 2.5" layer of sand? Im not sure of the grade of 2x10 but the work I have done so far shows a nice light reddish brown color when the wood is cut/drilled, perhaps Fir?

2" of sand weighs roughly 20 psf. This will substantially into available live load capacity. How large of an area are we talking about? You also have to consider the girder that is supporting the joists, and the footings that are supporting the girder.

I too concur with strucuraleng on this one. The weight is something you need to consider. While 20 Psf does not sound like a lot, it adds up quite quickly.
Have you considered removal of the ceiling below and then fastening the radiant heat then a reflective surface. This is a very common method to retrofit an existing home.
I would steer clear of adding such weight. Do not forget the expense in cutting trim, doors and if a stair case is involved the tripping issue on the top step when you reach the floor above.

Thanks for the replies. The house is a one story ranch with a 4' crawl space, the living area is a 30'x50' with two knee walls: both walls are double 2x10s as top plate with 2x10s on 16oc making up the studs. I agree with you both and will seek an alternative to the ledger.