Q: One visitor asked, "I just added to our house six months ago. It is a 15.5'X15.5' concrete slab with wrisbo in slab hot water heating. The finished grade of the slab is approx. 12" above the ground level. The concrete is protected underneath and all sides with 2" blue SM blue styrofoam. We do not feel there is an moisture problem as the concrete appears to have dried out with the in slab heating system.
We have just laid 5/8" T&G plywood using tapcon concrete screws at 16" centers.
We have purchased a lot of 3/4" X 2 1/4" random lengths pre finished oak flooring and intend to apply to the plywood sub floor. We will be bringing in the flooring and open all boxes for the flooring become climatized for a week before installing.
Do have any other suggestions and/or will this work. We have not laid down any poly as per some of your FAQ comments."

A: This installation over radiant heat can work. A lot depends on the design of the heating system and how it is operated, to lessen impact of sudden changes on the hardwood floor. You should also expect that there could be some shrinkage in the product and it may be a good idea to monitor the humidity levels in the home during heating season and add humidity as needed.
I will direct you to an excellent article dealing with this very matter. http://www.woodfloorsonline.com/ There, on this front page you will find a link to a lengthy article dealing directly with installing hardwood over radiant heated floors. I do hope this helps, and wish you success.