A chulha was used to prepare food. In the rural parts of India, people still prefer to cook on a chulha because it keeps the nutrients intact, the food doesn't lose its moisture and aroma and gives a smokey flavour. It is said that cooking on chulha also helps purify the surroundings.
Tea was also prepared on the coal or mud chulhas back in the time.
But as times progressed, we have forgotten this way of cooking and moved to the stoves, ovens and microwaves missing out on the smoky effect of the chulha on the chai.