Choosing Between a Top Damper and a Throat Damper in St. Augustine

Types of Chimney Dampers

There are two main types of chimney dampers on masonry fireplaces. The throat damper is a cast iron or steel plate in a frame, built into the top of the firebox and worked by a handle or rotating rod. The top sealing damper is a separate unit that mounts on the flue tile or crown and is opened and closed by a stainless cable that hangs down into the firebox.

Factory-built fireplaces use the damper designed into the unit, and any change there has to follow the fireplace maker's parts list.

How Well Each One Seals

A throat damper closes metal against metal. Even when new it leaves small gaps, and in a humid climate the plate and frame rust and warp over time, so many end up never quite closing. Warm, damp air drifts down the flue and into the room when the fireplace is not in use.

A top sealing damper closes a lid against a silicone gasket at the very top of the flue. When it is shut, the whole flue is closed off from the outside air, which also helps keep the flue walls from collecting condensation.

Rain, Animals and the Cap

A closed throat damper keeps rain and animals out of the room, but not out of the flue. Without a cap, water and nests can still collect above it. Many top sealing dampers come with a screen or hood, so when closed they work as a cap as well. Where a cap is already in place, some models fit under or replace it.

Gas Logs and Other Limits

A fireplace with a vented gas log set must keep its damper fixed open, as the log set instructions require, whichever damper type it has. A top damper can still be fitted, but it must be locked open. Very large, odd-shaped or multiple flues can also limit the models that fit.

Every top damper is installed to its maker's instructions, which set the flue sizes it suits and how it is fastened.

Repair the Old One or Change Type

If the throat damper still has a sound plate and frame, a repair may be all it needs: freeing the pivot, straightening the plate or replacing the handle. When the plate has rusted through or the frame has warped, a replacement throat damper may not be available to fit, and a top sealing damper becomes the practical route.

• Throat damper sound: repair it
• Throat damper rusted through: replace or switch
• Fireplace rarely used in humid months: a top damper seals better
• Vented gas logs present: any damper must stay open