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Short Stacked Masonry Chimneys

Masonry Chimney Diagram

Masonry Chimney Diagram

In order for a masonry chimney to be safe for use, it should be fully lined with terra cotta flue tiles that run continuously from the smoke chamber all the way up to the top of the chimney and penetrate the top of the crown by at least 2”. Each terra cotta flue tile should be mortared tightly together with no gaps, holes or spaces between the flue tiles. Each mortar joint should be completely sealed.

A “Short Stacked Chimney” is a chimney that doesn’t have enough terra cotta flue tiles to fulfill the above requirements.

“Short Stacked” chimneys occur when the mason building the fireplace and chimney doesn’t have enough terra cotta flue tiles to complete the job properly. Rather than making a second trip back to the brick yard in order to procure the neeed terra cotta flue tiles, the masons sometimes “cheat”, and the homeowner is left to deal with a potentially dangerous situation.

When faced with the fact that he doesn’t have enough flue tiles to complete the job, a mason will sometimes cheat by doing one of two things:

These spacers leave a dangerous gap that can allow carbon monoxide, creosote, gasses and open flames to escape.

These spacers leave a dangerous gap that can allow carbon monoxide, creosote, gasses and open flames to escape.

1. Fool the building inspector with spacers: Some unscrupulous masons may fool the building inspector by using some sort of spacers (usually red brick) in order to prop the uppermost one or two flue tiles up from the underside, making it appear from the outside of the chimney that the flue tiles are lining the entire length of the chimney from top to bottom.

Gaps and cracks in a chimney.

Gaps and cracks in a chimney.

This is a dangerous deception because the gap that is consequently created between the flue tiles leaves dangerous voids or gaps through which carbon monoxide, creosote, hot flue gases, and sometimes even open flames can escape and cause a structural fire!

If your chimney has this situation, it must be relined with stainless steel liner in order to render it safe for use.

AtoZ can remove the chimney's crown and install the required last bit of required terra cotta flue tile on top of the chimney.

AtoZ can remove the chimney’s crown and install the required last bit of required terra cotta flue tile on top of the chimney.

2. Not penetrate the crown by at least 2 inches: If the mason decides not to use spacers between flue tiles, he may simply decide to not penetrate the crown on top of the chimney by 2” and come up short. Rainwater is one of the most destructive elements a masonry chimney faces, and keeping water out of the chimney is of utmost importance. A flue tile that is even with or below the chimney’s crown will likely funnel water directly down the flue each time it rains.

This flue tile extends the correct amount of distance above the chimney crown.

This flue tile extends the correct amount of distance above the chimney crown.

This rainwater infiltration can erode the mortar joints between the flue tiles and your fireplace’s back brick wall, causing extensive damage. If your chimney’s terra cotta liners are coming up short, A to Z can remedy the situation by removing the chimney’s crown and installing the required last bit of required terra cotta flue tile on top of the chimney.

 

Overstacking flue tiles makes your chimney system less stable and more dangerous over time. Call on the pros at A to Z to restore your masonry chimney to safety.


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