There is a community created integration for NuHeat, but you will have to install custom code to make it work.
Begin by reading the following FAQ which explains the process for adding custom code to your account with the classic app.
[OBSOLETE] FAQ: An Overview of Using Custom Code in SmartThings (SmartThings Classic, Groovy Code)
Then if that sounds like something you would be interested in trying, here is the thread for the NuHeat integration:
Nuheat heated floor thermostat
[Release] Nuheat Signature Thermostat
You can ask any follow-up questions in that thread and people there will be happy to help. 