I personally like the DITRA heat by Schluter. Check out the Schluter Website for more info. {No, I'm not a salesperson for them.} I've seen it installed and it is pretty simple, works on any subfloor surface (including concrete), and is suitable for interior or exterior. The only snag is that it's really made for tile. They do make some very nice wood-look tiles if you're open to that.

We can heat just about anything, including wood. I would advise deciding on some flooring options you would like to use and then seeking out a suitable heating system. All too often we see people asking what type of flooring will work with their radiant heat after it is already installed and their options are limited to what works with the system.