2 wire system

[Snappy]

I have a 2 wire thermostat that controls my infloor heat. Can I just use the 2 wires or do I need to put a transformer in?

[BertG]

Firstly, You best check if your system is compatible for your Nest thermostat. 

If it is compatible: The Nest Thermostat i have required a "C" wire,a third wire,  even tho "C" wire  was suppose to be optional.