If you're talking about an underground pit, I've used them in the winter. Just make sure you burn enough wood to have a good deep hot coal bed to last through the cook.
If you mean an inground pit with the racks above the fire, just leave the ends of the pit open to be able to add more wood if needed.
sittin' by the campfire with my Brethren friends.
Lifetime member of the Society for the Preservation of Authentic Royal Magical Rare Kaskaskian Peppers (Thanks Ash :))