The heat accumulation rings are made up of cast iron discs, known for their extensive heat accumulation and conduction. The exhaust gases are forced through the rings, allowing the heat from these gases to be absorbed into the heavy cast iron mass. This heat is then slowly released into the surrounding area long after the fire is extinguished. They are usually mounted on the flue pipes of fireplace inserts but can be added to any fireplace. These rings are a good way of improving the heating performance of your fireplace.