In any sound meditation system, a good understanding of the concept of fire is important. What is fire? It is simply generated chi. How can we generate and manage chi? In meditation, ultimately it is through focused point meditation, that ultimate comes from one's Dantian or perineum (as a practitioner may like to choose) which again ultimately has to be subtly synchronized with one's breathing mechanism.
Our breathing mechanism is the external part an outside can see. It is therefore oftentimes viewed by non-practitioners (and novice practitioners) as the primary (or only) mechanism for chi or fire generation. Of course, they are wrong. Taoist masters like Grandmaster Wu Chongxu (伍沖虛) of Wu-Liu group (伍柳派) liked to differentiate breathing with "true-internal-breathing" (真息). It is a nice way to teach students not to take (lung) breathing as chi generation per se, but the concept "true-internal-breathing" still begs the question of "what is this after all?" The clear conclusion is that there is no single concept to represent the concept of fire. One has to learn and experience its subtleties step by step. And Master Wu didn't fail to warn practitioners the management of fire will have subtle difference during different stage of one's practice. My view is that despite the complexity of the concept, Fire is still the best metaphor for practitioners to appreciate, learn and experience the different manifestation of the ch generation and control purpose.
What is the best way to experience this concept of Fire? It all depends on individual practitioner's personal preference and/or uniqueness. For example, many Buddhists meditative practitioners in Japan like to do their meditation under a (sometimes freezing) water fall. And they even use this as a training tool for beginning meditators. Interested readers can check on my previous post: Do you shiver? The truth is that if one can start one's internal fire, one will not shiver!