Which way to turn a knob to increase?

Clockwise tightens and decreases heat, counterclockwise loosens and increases heat.

1. Which way do you turn a knob?
2. What does knob on radiator do?

Which way do you turn a knob?

I think people will understand that better than left and right, it's far more descriptive. It is always better to use clockwise or anti-clockwise as these are not confusing as right and left. Although they do mean the same and both ways of explaining the turning of a knob is acceptable.

What does knob on radiator do?

They allow you to control how much heat you want your radiator to give out, just like a tap to control the flow of water. Each radiator will have two valves. One will control the amount of hot water that enters the radiator and the other will balance the system by controlling how much heat comes out of your radiator.