Can I Use an Insert if My Fireplace Is Too Big & Has No Damper?

Oversized Flues

• An oversized flue occurs when you have a fireplace that is too small for its chimney. This creates a large area of airflow directly above the fireplace, which is not good for the pressure conditions that the fire needs. A flue that is too large can actually allow air to stream down into the fireplace and keep flames from properly igniting. However, a firebox may be able to limit the amount of airflow a fire receives regardless of the chimney size.

Damper Substitutes

• The damper allows you to partially close the flue in order to properly manage air flow. Typically, a damper for a normal wood fireplace is necessary, especially when you aren't using the fireplace at all. In this case, fireplace inserts may come with dampers of their own, attached to the insert, that you can use. Even if they do not, you can install a damper at the top of your chimney with a control cable running down to help control air flow.

Creosote Issues

• If your fireplace has a large cavity at the start of the chimney, this may be an issue even if you buy an insert that is large enough to properly fit in the space. If the chimney is too large, then the smoke can linger instead of being forced up the chimney. In lingering, it can build up creosote deposits on the walls of the flue as it cools. This can create serious fire hazards. If your chimney is wide, not just at the hearth but up through the wall as well, you may want to consider remodeling when you install your insert.

Electric and Gas Inserts

• Keep in mind that not all fireplace inserts will have problems with dampers and flues. An electric insert will use a heating element to produce heat and does not have any exhaust at all, allowing you to seal up your chimney. A gas insert may use the chimney but you will be able to install a more direct exhaust vent through the wall or ceiling and bypass any damper issue.