Most products to seal a fireplace are inflatable balloons or pillows such as the Fireplace Draftstopper, the Chimney Pillow or the Chimney Balloon. These devices form an insulating plug to stop back drafts and heat loss.
The design of a fireplace draws warm air from inside the home through the flue. When the fireplace is in operation, this removes smoke the fire creates. However, when the fireplace is not in operation, the flue draws air out of the home after the furnace warms it. While many fireplaces have dampers, the metal often warps due to the heat of the fire, so they become ineffective at blocking heat loss.
Older fireplaces often include a summer plate. The cast-iron plate is often not effective at preventing heat loss. Glass doors also continue to allow the escape of heat up the flue.
The heat loss from a fireplace can add up to 30 percent on a home heating bill. The open flue allows dust, soot and other materials to fall into the fireplace. Inserting an inflatable flue blocker into the opening provides an insulating cushion of air that stops the heat loss while preventing debris from littering the inside of the firebox.
These devices provide a temporary flue block. Most are removable if the owner decides to build a fire. Once the fire is out and the embers are cold, he reinflates the device and returns it to the flue.