问曰：“何谓炉？”
question: what is the stove?
答曰：“上品丹法，以神为炉，以性为药，以定为火，以慧为火。中品丹法，以神为炉，以气为药，以日为火，以月为水。下品丹法，以身为炉，以气为药，以心为火，以肾为水。又有偃月炉、玉炉。”
answer: the highest level elixir method uses the “Shen” (consciousness) as the stove, the “Xing” (natural consciousness) as the medicine and being set as fire.
the middle level elixir method uses the “Shen” as the stove, the Qi as medicine, and the sun as fire. The lowest level elixir method uses the body as the stove, the qi as the medicine, the heart as the fire, and the kidneys as water. there is also the moon lying in the lake as the stove, and the jade stove.”
– taken from the document “Golden elixir, question and answers.”