Why is my heater blowing cold air?

My 2011 Jeep Compass heater is blowing cold air all the time. Any ideas on what is wrong?

Which tyres are best for the Jeep Compass?

I'm need new tyres for my three year old Jeep Compass, but am not sure what tyres to fit. The size is 215/55/18 V95, currently on original Continentals, would it be better to change? I'd like a quiet...