Chimneys. Chimneys should extend above adjacent ridges to avoid a down draft. One or two bricks should be left out at the bottom of the flue, to allow it to be cleaned easily and the hole should be fitted with an iron cover.
If the chimney is more than three stories high, and if the best results are wanted, its walls should be double thick for a third of its height, as the smoke is kept warmer, thereby assisting the draft. For this reason, a chimney in the center of a house is more apt to draw better than one which is a part of the outside wall. A round chimney usually draws better than a square one. The flues of a chimney should be no larger than necessary, as the smoke cools, thereby decreasing its tendency to rise.
A chimney should not be plastered inside, though it is the custom in some localities. Experience has shown that the mortar will drop off as the chimney expands and contracts, often taking the pointing from between the bricks with it; this fact is so well established, that a chimney plastered in this way will be condemned in most large cities.