What is the difference between a zero clearance and a full masonry fireplace?

A zero clearance fireplace has an insulated metal jacket around the fireplace that allows it to be placed right up against interior or exterior walls with 2″ inches between the fireplace and combustible materials. Heated air is circulated within the fireplace unit and blown out into your home. A Masonry Fireplace uses masonry block around the unit which creates a heat chamber. The heat chamber then has a vented area which allows the heated air to circulate into the room.