229. In planning and building brick chimneys, the chief things to be considered are the height of the chimney, and the number, size, and arrangement of the flues.

To make the chimney "draw properly," a separate flue should be provided, extending from each fireplace to the top of the chimney. The furnace in the cellar and the kitchen range may connect with the same flue, and, as the range fire heats the flue and is above the furnace, the furnace draft is often better when connected with the range flue.

For ordinary stoves, and where a small furnace is used, the flues may be the usual size, 8 in. X8 in., or the space taken by two bricks. If the furnace is a large one, it is better to make the flue 8 in. X12 in., and the same size should be used, when possible, for fireplaces having large open grates.

Sometimes smoke flues are made only 4 inches wide. But they soon become choked with soot and are difficult to clean. It is well not to make a chimney flue less than 8 inches.

Smoke flues should always be lined with some fireproof material; in fact, the building laws of large cities provide for this. The lining is usually of fireclay, tile, or else of galvanized-iron pipe. If the pipe used is round, the space between it and the walls of the chimneys may be utilized for ventilating the rooms through which the chimneys pass, by putting ventilators in the wall of the flue. The outer walls of chimney flues should be 8 inches thick if flue linings are not used, to prevent the smoke becoming chilled too rapidly.

230. Insufficient height causes more smoky and badly drawing chimneys than any other cause. Chimney flues should, whenever possible, extend above the highest point of the building or those adjoining it. If this is not done, eddies may be formed by the wind passing over the higher parts of the roof and causing a downward draft in the chimney flues, under which circumstances they are sure to smoke. This may be obviated, when the chimney is not carried high enough, by using a hood having two open sides. Hoods are unsightly in their appearance, and their use should be avoided when possible.

231. Chimneys were formerly pargeted, as it was called; that is, the partitions, or withes, of a chimney were plastered with a mixture of cow manure and lime mortar. This is now seldom or never used; if it is deemed necessary to parget the inside of a chimney, Portland cement makes the best material to use. This is not affected by heat and will prevent sparks or air passing through the cracks, and also increases the draft. When an iron or fireclay tile pipe is used, pargeting is unnecessary.

Chimneys 96

Fig. 94.

232. During the building of a chimney, pieces of brick and lumps of mortar will drop down in the flue; therefore, a hole should be left at the bottom, with a board put on a slant to catch the falling mortar. After the chimney is topped out, the board and mortar can be removed and the hole bricked up.

Where bends occur in the flue, openings should be left in the wall to clean out any pieces of brick or mortar that may have lodged there.

233. Fig. 94 shows vertical and horizontal sections of a double chimney running through five stories, with fireplaces on each floor. The section a-b shows the way the chimney is "topped out" and the arrangement of the flues. The fireplaces on the different stories, and the run of the flues are shown at c-d, e-f, g-h, and j-k; l-m shows the sectional views of the range chimney in the kitchen. The flues are shown as 8 in. x12 in., as affording a better draft than 8"x8" flues for open fireplaces. If stoves are to be used, or if the space is valuable, 8" X 8" flues may be substituted.

Chimneys 97

Fig. 95.