Fireplace Damper Types: Throat, Top-Mount and More

What every damper has to do

Whatever its shape, a damper has two jobs. With a fire burning it must open fully and stay open, so smoke and gases leave the house. With no fire it should close as tightly as possible, so the chimney stops pulling warm air out of the room and stops letting rain, cold air and animals in. The types differ mainly in where they close the flue and how well they seal.

Older dampers were designed mostly for the first job. Many seal poorly by modern standards even when new, which is why a gap or a draft around an old throat damper does not by itself mean it is broken.

The main types side by side

These are the dampers we come across in homes across the region, from Long Island colonials to Philadelphia rowhouses.

Throat dampers

The throat damper is the classic type in masonry fireplaces. It is a cast iron or steel frame set into the narrow throat just above the firebox, with a hinged plate that swings up and back to open and drops forward to close. When it is open you can see up into the smoke chamber; when it is closed the plate lies across the opening and blocks the view.

The control tells you a lot about how old the setup is. Poker-style dampers with a notched rod hanging down are common in mid-century fireplaces; rotary knobs on the face of the firebox and ratchet levers appear in others.

• Poker or push-pull handle hanging down from the front of the throat
• Rotary control: a knob or crank on the face of the firebox
• Lever or ratchet handle at the top of the opening
• Chain on some round or older dampers

Top-mount and top-sealing dampers

A top-mount damper sits on the top of the flue tile, outside, either under a cap or built as part of one. A spring holds the lid open and a stainless cable drops through the flue to a bracket and handle on the firebox wall. Pull the cable down and hook it to close the lid on its gasket; release it and the spring opens the lid.

Because the seal is at the crown, the flue stays out of the weather and animals cannot get in. The column of air inside the chimney also stays a little warmer between fires. Top-sealing dampers are a common replacement when an old throat damper is rusted, broken or mortared in where it is hard to reach, and they are visible from the street as a low box or lid on the flue top.

Factory-built fireplaces and stovepipes

Factory-built, or zero-clearance, fireplaces have a damper built into the metal unit by its maker, usually a plate or round blade worked by a handle, pull ring or chain. Replacement parts and adjustments follow that unit's manual, and the damper is not swapped for a masonry-style one.

Round flues, including some stovepipes, can carry a key or butterfly damper: a disc on a rod that turns a quarter turn to partly close the pipe. Many modern stove makers do not call for a pipe damper at all, since the stove's own air control regulates the fire, so follow the stove's manual before adding or using one. Inserts with a liner usually have the old throat damper taken out to make room for it.

Older and unusual fireplaces

Brownstones and rowhouses from the coal era often have shallow fireboxes with a cast iron front or summer cover and a very narrow throat, sometimes with no damper at all. Some had a sliding or hinged iron plate built into the insert, and many of those have rusted away. Rumford fireplaces, tall and shallow with a streamlined throat, need a damper shaped for that throat or a damper at the top.

In any of these, the first question is whether there is a working damper to set. Draft stoppers and inflatable plugs are sometimes mistaken for dampers, but they are only temporary blockers for an unused fireplace and must come out before any fire.

Where the fireplace damper is

Kneel in front of the cold firebox with a flashlight. Reach up behind the top front edge, the lintel, and you will usually feel the damper frame and its control within reach. A handle hanging down or a knob on the face of the firebox belongs to a throat damper. Wear gloves: the frame and smoke shelf are usually coated in soot and rust scale.

If you see a cable running up the inside of the flue to a bracket on a side wall, you have a top-mount damper. If you see straight up to daylight with no plate at all, the damper may be missing, rusted away or stuck fully open, and a chimney inspection is the next step.

Keeping each type working

Throat dampers last longest when they move. Opening and closing one through its full travel every few weeks, even out of season, keeps rust from locking the pivots, and a sweep visit should include brushing the plate and clearing soot and debris from the smoke shelf behind it, where rust scale and fallen mortar collect.

Top-sealing dampers need a different kind of attention. The cable should run straight and hook securely, without fraying where it passes the bracket. The gasket on the lid wears and hardens with time and sun, and a worn gasket lets air and water past. In an ice storm the lid can freeze shut, so leave it alone until it thaws rather than yanking the cable. Factory-built units and stovepipe dampers follow their own manuals for inspection and parts.

Which type suits your fireplace

A sound throat damper that opens fully and closes reasonably well is worth keeping and maintaining. One that is warped, rusted through or mortared in beyond easy repair is often replaced with a top-sealing damper rather than cut out, as long as the flue top and crown are in good shape for mounting. Coal-era and Rumford fireplaces may need a damper made for their throat, or a top-sealing damper sized to the flue.

On a visit we identify the damper you have, check how it opens and seals, look at the chimney top, and tell you which options actually fit your fireplace.