Fireplace Structure Guide

In this guide to fireplace structure, let’s look at the internal structures of a built-in fireplace and their significance:

The mouth - this is where the combustion takes place. The size and placement will determine the amount of heat radiation in the room, and also the extent to which the flames can be viewed. It’s advisable to search for the ideal configuration for both parameters, bearing in mind the room’s size. A rectangle lying on its side is the ideal shape for the opening. The volume of the room and the size of the chimney shaft will determine the height and width of the opening.

The grate - this is usually made of wrought iron, and the logs to be burned are place on it. The spacing of the bar should allow only the ashes, not the firewood to fall through. It must also be designed to allow ventilating air to enter – if not, the fire will go out.

The ash dump - situated under the grate, it serves to collect the ashes that result from the combustion. It’s usually hidden below the mouth of the fireplace with a removable drawer, to make it easy for ash removal.

The air entrance - this is indispensable for all open fireplaces as it guarantees the optimum combustion. One possibility is simply take advantage of the sealing off of a home’s doors and windows from the exterior. Another option is to have gaps that open onto the lower part of the ash dump.

The fire hood - it extends from the upper edge of the mouth of the fireplace to the smoke chamber. Its purpose is to extract the fumes and prevent them from coming out through the mouth.


The throat - this runs from the lintel over the mouth of the fireplace before narrowing down the dome damper where it connects with the smoke chamber. It regulates the passage of smoke and fumes and enlarges or reduces the opening of the throat, blocking the entrance of cold air, which would speed up combustion and cause heat loss into the atmosphere.

The smoke chamber - It’s a slanted, bag-shaped space following immediately on from the throat of the fireplace. It prevents sudden draughts of cold air from pushing smoke into the room.

The smoke pipe - this is the final stage of the smoke extraction system. Its tube shaped and narrows up from the smoke chamber before opening onto the exterior. Normally it’s crowned with a hood or cap, which sticks out from the roof to provide protection from the elements like the sun, snow and rain.


Besides this guide to fireplace structure, you may also want to take a look at:

Contemporary fireplace

Fireplace placement guide

Fireplace materials

Living room decorating guide


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