The problem is with my energy cost, which is around €0.17/kWh. Do I think it will be viable? 
It depends; if you have a shed or a small guest bathroom that is heated with electricity anyway for instance, you don't burn any more money when switching from a resistive to a 'semiconductor-based' electric heater.No... I use the heater very little. So in general it would be a consumption amenity.
The consumption is 140w per hour, right?
Well, accounts can also vary based on the value of Bitcoin. Today it may not be very profitable and tomorrow it will be.