When it comes to traditional open masonry fireplaces, masons have perpetuated outdated ideas about the smoke shelf, the mysteries of the smoke chamber, and the need for wide, but shallow-throat dampers. Today, it is clear that all three of these features work against successful fireplace performance (see Figure 1).   Figure 1. Traditional fireplaces leak smoke into living space and don’t produce heat efficiently. The curving smoke chamber, the throat damper, and the smoke shelf all decrease the stability of the chimney draft. The smoke shelf and shallow-throat damper both act as obstacles to straight exhaust flow. And the smoke chamber actually reduces the strength of a chimney’s draft by slowing and cooling the fireplace exhaust. The performance of many brick fireplaces can be improved immediately by removing the throat damper and smoke shelf, and installing a chain-operated damper at the top of the chimney. The results are a smooth, straight path for the exhaust and less smoking when a fire burns.

Makeup Air While improper design and location is a major cause of poor fireplace performance, tighter house construction and powerful exhaust fans must share some of the blame. By installing vapor barriers and using doors and windows that have sealing gaskets, builders commonly reduce air leakage by more than 75% compared with the standard...

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