Fungus gnats are small, dark, short-lived gnats, of the families Sciaridae, Diadocidiidae, Ditomyiidae, Keroplatidae, Bolitophilidae, and Mycetophilidae (order Diptera); they are sometimes placed in the superfamily Mycetophiloidea. The larvae feed on plant roots and fungi, helping in the decomposition of organic matter.
In each of these situations, you experienced the work of the three types of heat transfer: conduction, convection, and radiation. Conduction, or direct heat, occurs when the faster moving molecules of the fire collide with the cooler molecules of the marshmallow, causing them to move faster and become hot.
The temperature inside is governed by two things, first how much heat is supplied (using a heater etc.) and how much heat is dissipated to the outside. The rate of transfer is directly proportional to the difference in temperatures between the inside. So for example, if the difference between inside and outside is 0, then the heat transfer will be zero. If there is a 5 degree difference the heat transfer will be half as much as if the difference was 10 degrees.