he size of opening must of
course be in proportion to the dimensions of the room, but one with
lintel less that 26 inches above the hearth is not practical because
of difficulty in tending the fire. A good maximum height is 42 inches.
The width should be in accord and exceed it so that the opening is a
well-proportioned rectangle with its greater dimension horizontal.

In our country home, built about 1765, there are three fireplaces,
each of different size and proportions. The largest, where the cooking
was done, is 50 inches wide by 37 inches high and 18 inches deep. The
one in the old parlor has a width of 38-1/2 inches, a height of 28-1/2
inches, and a depth of 13-1/2 inches. The smallest has an opening just
off the square which is 27 inches wide by 25-1/2 inches high with a
depth of only 11 inches. All three are non-smokers under all
conditions of wind and weather. With proper size of wood they are easy
to tend and good sources of warmth except in real winter weather. Each
is individualistic in hearth dimensions, the largest of course being
that of the old kitchen with a hearthstone over seven feet long by two
feet wide.

Whether heat radiates into the room, or goes up the chimney along with
the smoke, depends on the angles of fireplace sides and back. The
former should be set at an angle of about 60 degrees so that they
flare outward from the back wall. There are two schools of thought
regarding the back. One would have the forward pitch begin one third
of the distance from floor to lintel; the other favors the slope
starting at the bottom and continuing upward in an unbroken plane. In
the former, the pitch should be about 23 degrees from the vertical;
with the latter, 18 degrees will suffice.

From this point the consideration of dimensions goes up the chimney.
In its standard ordinance for chimney construction, the National Board
of Fire Underwriters calls for fireplace flues with a draft area of
one-twelfth of that of the fireplace opening and determines this area
as a circle or ellipse that will fit within the tile used to line the
flue. As it is difficult to obtain flue linings of exactly the desired
area, it is better to select a size slightly larger, rather than one
smaller, and so make sure of sufficient capacity under all weather
conditions.

Between the lintel of the fireplace and the point where the flue
commences come the three structural features so stressed by Count
Rumford. They are the throat,