A properly designed damper, as shown in figure 34, affords a means
of regulating the draft and prevents excessive loss of heat from the
room when the fire is out. A damper consists of a cast-iron frame
with a lid hinged so that the width of the throat opening may be
varied from a closed to a wide-open position. Various patterns are
on the market, some designed to support the masonry over the opening,
others requiring lintel irons.
[Illustration: Figure 38.--This well-designed small stone fireplace was
built in accordance with the principles given in this bulletin. It is a
good heater and does not smoke. The jambs are wide enough to resist the
thrust of the arch.]
A roaring pine fire may require a full-throat opening, but slow-burning
hardwood logs may need only 1 or 2 inches of opening. Regulating the
opening according to the kind of fire prevents waste of heat up the
chimney. Closing the damper in summer keeps flies, mosquitoes, and other
insects from entering the house down the chimney.
In houses heated by furnaces or other modern systems, lack of a
damper in the fireplace flue may interfere with uniform heating,
particularly in very cold windy weather, whether or not there is a fire
on the hearth. When air heated by the furnace is carried up the chimney
there is a waste of the furnace fuel, but a damper partially open serves
a slow fire of hardwood without smoking the room or wasting heated
air from the main heating system.
[Illustration: Figure 39.--Diagram showing front view and cross section
of an entire chimney such as is commonly built to serve a furnace,
fireplace, and kitchen stove. Two sets of dimensions are given, those in
rectangles refer to the approximate sizes of the voids or openings; the
others refer to the outside dimensions of the brickwork. These are used
in estimating the number of bricks in a chimney. The letters _A_-_F_
indicate sections used in estimating the quantities of brick required
(See p. 44.)]