Do You Have to Use Flue Blocks to Build a Chimney?

Flue Block Chimneys

• Flue blocks are precast concrete blocks designed to help you construct a chimney. These blocks come in square or rectangular shapes and have a hollow center. When you build a chimney with flue blocks, you simply pile them on top of each other until they reach the appropriate height to form a chimney. You can place a flue liner inside the hollow area created by these blocks or simply use the hollow area as the flue itself. Some flue blocks have small holes in their sides. These holes line up to create tube-like structures into which you can pour concrete to reinforce the structure of the chimney. You can surround flue blocks with bricks to strengthen them or leave them bare.

Chimneys Without Flue Blocks

• You don’t ultimately need flue blocks to build a chimney; instead, you can use traditional masonry materials to simulate the effect of flue blocks. In fact, flue blocks exist as a short cut for traditional masonry methods. Traditional masonry chimneys begin with a flue liner. To build these chimneys, you install a flue liner on top of the fireplace and build a frame around this liner. Chimney builders usually use bricks and mortar -- a binding agent, like glue -- to create this outer layer. The brick in these chimneys serves the same purpose as a flue block, by framing the flue liner. In some instances, builders pour concrete over the brick to reinforce the chimney structure.

Benefits of Flue Blocks

• While flue blocks prove unnecessary in chimney construction, they provide two key benefits. First, they help the average homeowner. You may not know how to build an entire chimney with brick and mortar, but most people can construct a basic chimney from flue blocks by following the instructions provided by the manufacturer. Flue blocks also help create chimneys within the frame of an existing building. When building a new fireplace, you can install flue blocks to create a flue without tearing apart your walls to build a brick chimney.

Building Codes

• Always refer to your local building codes before constructing a chimney. If you want to use flue blocks for your chimney, make sure their use conforms to local codes. The building code for Allegany County, Pennsylvania, for instance, requires that you fill all flue block cores, or hollow areas in the structure of the block, with mortar or concrete. If you’re confused about anything in your local building code in regard to chimney construction or flue blocks or need a second opinion or expert advice, contact your local building commission or a contractor. Avoid beginning chimney construction without a clear plan for finishing it or a full knowledge of your materials.