For performing Vedic sacrifices, duly consecrated fires are needed. The maximum number of such fires is five and they are called ‘pañcāgnis.’ They are: gārhapatya, āhavanīya, anvāhāryapacana or dakṣiṇa, sabhya and āvasathya.
The word ‘āvasathya’ is derived from ‘āvasatha’ or a dwelling place. According to one view, the brāhmaṇas and others who were invited to participate in a sacrifice used to be put up in special dwelling places called āvasatha (similar to a modern dharmaśālā) where a fire was to be lit, to ward off cold. This could have been the origin of this fire.
During Vedic sacrifices, this fire is stationed to the east of the sabhya fire, in a hut called ‘āvasatha.’ The hearth is triangular in shape, each side being 25 aṅgulis (aṅguli = finger’s breadth).
Some authorities of Vedic sacrifices held its establishment compulsory and others as optional. For establishing it, the original fire had to be brought from the gārhapatya.