Xu Ci Shu’s Discourse on Fire.
The fire must use hardwood charcoal, which is regarded as the best material, then the wood nature is unexhausted. When there is too much smoke, then the smoke will enter the boiling water, the boiled water then necessarily becomes useless. Therefor, first burn the charcoal to red to rid it of smoke and flame. At the same time, get a strong, vigorous burning fire. The water then easily boils. After the charcoal is already red, then place the water kettle over it. At the same time rapidly fan the stove - the quicker the better: do not stop your hand. Hot water that had stopped boiling is preferably discarded and fresh water boiled again.
-Xu Ci Shu
The ancient art of Tea, Wisdom From the old Chinese Tea Masters.