While seated, on a cold night, next to a fireplace, thoughts start racing across your mind. You wonder why the past was so beautiful unlike the present. Then still in the same position, you wonder how the heat from the fireplace reaches you without passing through any medium. You even recall your physics teacher saying that air is an insulator. So how did the heat reach you?
Scientifically, most of the heat that reaches you does so not by means of air but rather through radiation. Simplest reason is that air is a good thermal insulator and therefore can do much little to make heat reach you.
The only way the heat could have reached you is through radiations. Radiations require no medium to travel. Thermal radiation, specifically, is composed of electromagnetic waves which in most cases are infrared waves and visible light. These waves are emitted by heated objects. The radiations carry energy which is converted into heat when striking a hard surface.
Thermal radiation always spread in all direction. Enabling it to spread throughout the room from the fireplace.