Do I Have a Hidden Chimney?

Brick Chimney Types

• In addition to their use for venting fireplaces, older homes that used coal or gas for heating as well as wood for cooking, needed ventilation flues. These venting chimneys are often found inside the walls between kitchens and dining rooms, especially in Victorian, box style and Craftsman bungalows. They were also necessary for dual-function stoves that were used for both cooking and heating. Hidden chimneys were typically much smaller than fireplace chimneys because they were only used to evacuate hot waste gases from various household appliances.

Basic Chimney Construction

• People living in older homes have modified them to make them more compatible with modern lifestyles. Many early homes still have brick fireplace chimneys and flues. The repeated burning of natural gas in furnaces, stoves and water heaters causes the build-up of moist acidic gas that erodes the alkaline mortar between the bricks of hidden chimneys. The acid of creosote, which is created by burning wood in fireplaces, does the same thing. Eventually, the acidic build-up erodes the overall chimney structure, making it susceptible to collapse.

Improved Chimney Construction

• The mortar of terracotta-lined flues doesn't deteriorate as quickly as the old mortar, but it is not sufficiently energy efficient or structurally strong enough to withstand potential earthquakes, particularly those along the fault lines in California. In addition, they allow rain to enter, but they don't allow enough of the gases to escape to prevent a build up of carbon monoxide in the home. Prolonged use of these hidden chimneys as flues for furnaces or water heaters softens the brick, making it increasingly unstable.

Removing Hidden Chimneys

• Modern appliances don't require brick flues. Kitchen or dining room renovations provide the perfect occasion to remove these energy-draining obstructions that serve no purpose. Enlist a qualified professional to remove a hidden chimney to protect the historic integrity of the home. It may be necessary to remove a small amount of an interior wall, but because the chimneys rarely provide structural support, it shouldn't be necessary to install framing before removing the bricks. Once the bricks are removed, they can be used to create a herringbone-patterned walkway or patio. The removal of hidden chimneys lessens the risk of significant structural collapse due to a major earthquake.