The Netdiuno only supports one wire temp sensors in a branch release of 4.1
Plus the netduino has some serious difficulty with regulating power over USB. You may have more stable readings if you use the power block instead.
And one more downer, I have a lot of trouble with reliable sockets and the netdiunos smallish memory space limits its capability.
Reliability is extremely important for something like running a heating element. My opinion is choose a different micro controller to work with. FEZ for example. The hydra is similarly priced and way more capable, stable and supports gadgeteering.