A quick note to add to Oak & Broad and Masterpiece Hardwood. The type of flooring (engineered or laminate) will also have limitations as to WHICH TYPE of under-floor heating. Electric radiant floor heating is possible...but many manufacturers don't like it because it tends to over heat. To work with electric radiant heat you will need to ask the flooring manufacturer AND sink it in cement (the mats are not something that manufacturers like to offer warranty for). Hydronic heat (water/gel/oil) is the most expensive but it is also the one that almost everyone allows their floors to be laid over top. If radiant heating is allowed with the floor, the hydronic will be the one accepted by the flooring manufacturers.

Electic = cheaper but has the most limitations with flooring products. Hydronic = expensive with the least amount of limitations....almost everything works with hydronic.