Figure 19.—In 1744 Franklin promoted a metal fireplace of this type to be set out into a room. These are known as Franklin stoves and sometimes are equipped with andirons for burning wood or a grate for burning coal. The metal blower, shown in front of the opening was used with grates and set in place when starting the draft and then removed so that the cheery heat of glowing coals could be enjoyed. At one time this type of stove was highly thought of because it threw out more heat than the built-in fireplace. A few manufacturers specialize in Franklin stoves because of the present-day demand.
Tests conducted by this Bureau indicate that, as ordinarily constructed, a fireplace is only about one-third as efficient as a good stove or circulator heater. Nevertheless, they have a place as an auxiliary to the heating plant and for their cheerfulness and charm. In milder climates, fireplaces may suffice as the sole source of heat; also certain materials often wasted may be utilized for fuel. The disadvantages of the ordinary fireplace are lessened by "modified" fireplaces.
The Franklin stove ([fig. 19]) is a type of modified fireplace.
The modified fireplaces of today are of several types, as shown in figures [20] and [21].
Both the last two types of modified fireplaces are manufactured as units of heavy metal, designed to be set into place and concealed by the usual brickwork, or other construction, so that no practical change in mantel design is required by their use. The modifications are built-in standard parts of the fireplace—only the grilles show ([fig. 22]).
Figure 20.—In this modified fireplace air enters the inlet, a, from outside and is heated as it rises by natural circulation through the back chamber, c, and the tubes, t, being discharged into the room from the register, b. Air for supporting combustion is drawn into the fire at d and passes between the tubes up the flue A damper is also provided to close the air inlet.