Does an Outdoor Fireplace Need a Damper or a Cap?

What a Damper Does Indoors

A damper is a hinged metal plate in the throat or at the top of the flue that closes the chimney when the fireplace is not in use, so the house does not lose its air up the flue. Chimney safety guidance stresses that it must be fully open before a fire is lit; lighting a fire against a closed damper fills the room with smoke.

Florida's residential code builds that in. Section R1001.7.1 requires a masonry fireplace to have a ferrous metal damper at least 8 inches above the top of the opening, operable from the room containing the fireplace.

Masonry Outdoor Fireplaces

The code section does not carve out outdoor fireplaces, but it was written around a room. On a patio there is no conditioned air to lose, so the main job of a damper is gone, and what is left is keeping weather out of a flue that is not in use. Whether your building official expects a damper in a masonry outdoor fireplace is a question for the plan review, and we build to the answer the county gives.

A damper that is fitted outdoors has a harder life. It sits in rain and humid air between fires, so it needs to be checked for rust and freed before every season.

Factory-Built Outdoor Units

Factory-built outdoor fireplaces follow their listing, and some have no damper at all. The manual for one outdoor wood-burning model listed to UL 127 says plainly that there is not a flue damper, and that the unit therefore cannot be installed indoors. Its chimney ends instead in a termination cap listed for that system.

Rain, Leaves and Animals Come Down the Flue

Without a damper, the top of the chimney is the only thing between the weather and the firebox. That outdoor fireplace manual lists birds' nests and leaves in the termination cap among the causes of a fire that smokes or will not draw, and says the unit keeps out some rain but is not waterproof.

• A masonry chimney gets a sloped concrete, metal or stone cap with a drip edge, under section R1003.9.1.
• A rain cap over the flue needs at least four times the flue's open area beneath it, under R1003.9.3.
• A spark arrestor screen, where fitted, keeps birds and animals out as well as sparks in.
• A factory-built chimney uses only the cap listed for it, with nothing blocking its air holes.

Draft Without a Damper

A damper does not make a fireplace draw; the flue does. Section R1003.11 requires a masonry chimney to be lined, and the flue has to be sized to the opening and tall enough to clear nearby roofs. Our guide to outdoor fireplace dimensions covers the proportions, and the guide to an outdoor fireplace chimney cap covers the top.

A Top-Sealing Damper on an Outdoor Chimney

Chimney safety guidance notes that a tight-sealing damper mounted at the top of the flue cuts the air drawn down a chimney. On a masonry outdoor chimney, the same kind of damper also closes the top against rain and nesting animals between fires, where the flue size and the cap allow it. Fitting one is top-sealing damper installation work.

Our local, family-owned team has experienced chimney technicians, and the free inspection of the fireplace and chimney comes with a written estimate. We are Proudly American and plain spoken, and a Proudly American answer may be that your outdoor chimney needs a damper, a cap or nothing at all.