Dear Martin,
here is a reference to northern and southern fires in the context of wedding preparations. The fires are explained by Devapāla as non-sacrificial (laukika).
Kāṭhakagṛhyasūtra 19.3:
[...] vā dvāv agnī prajvālya dvau paśū upākaroty aryamṇe dakṣiṇaṃ, prājāpatyam uttaram ।
(Devapāla’s Bhāṣya)
[...] laukikau dvāv agnī prajvālya dvau paśū chāgau kanyāsaṃskārārtham upākuryāt । paśukalpavat । ekam aryamṇe dakṣiṇabhāgavartiny agnau, dvitīyaṃ prajāpataye uttaradigbhāgavartiny agnau [...]
(Quoted from Raik Strunz' forthcoming edition).
Best wishes,
Walter