At the heart of the sign there is a circle that is a cardinal and a central element in the symbols of metals. Examples - iron, aluminum, copper, etc.
The arrows rotating around the center (red - the main color denoting heat (e.g. on different devices, etc., in this case, the warm air, blue - basic color denoting cold) symbolize the ventilation of air (warm and heavy - up, cold and light - down), and the metal intervals between them show that the process occurs by means of ventilation of metal structures.
The gradient version