The quantity and temperature of the heated air discharged from the grilles in figures 20 and 21 were measured to determine the merits of the convection features. These measurements showed that very appreciable amounts of convected heat are produced by the modified unit when properly installed and operated. Discharge-air temperatures in excess of 200° F. were attained from some of the units tested. The heated air delivered from the discharge grilles of some of the medium-sized units represented a heating effect equivalent to that from nearly 40 square feet of cast-iron radiation of the ordinary hot-water heating system, or sufficient to heat a 15- by 18-foot room built with average tightness to 70° F. when the outside temperature is 40° F. Additional convected heat can be produced with some models by the use of forced-circulation fans. [Illustration: Figure 22.--Except for the registers and metallic sides and back, the appearance of modified fireplaces is like that of ordinary ones. An interesting effect is secured by the mirror--the reflection of the opposite wall appears like a recess over the mantel.] However, the nature of operation, with the unavoidably large quantity of heated air passing up the stack, makes the inherent over-all efficiency of any fireplace relatively low. Therefore, claims for an increased efficiency of modified fireplaces should be understood merely as constituting an improvement over the ordinary fireplace and not over stoves or central heating plants. When a fireplace is being selected the kind of fuel to be burned should be considered; also, the design should harmonize with the room in proportion and detail (figs. 23 and 24). [Illustration: Figure 23.--A well-designed commercial mantel that suits the room. Since it is painted the same color as the walls, it does not focus attention, as the handsomely carved formal mantel or mahogany shown in figure 37 is intended to do.] In colonial days, when cordwood was plentiful, fireplaces 7 feet wide and 5 feet high were common, especially when used in kitchens for cooking (fig. 25). They required large amounts of fuel and too frequently were smoky. Where cordwood (4 feet long) is cut in half, a 30-inch width is desirable for a fireplace; but, where coal is burned, the opening can be narrower (fig. 26). Thirty inches is a practical height for the convenient tending of a fire where the width is less than 6 feet; openings about 30 inches wide (fig. 27) are generally made with square corners. The higher the opening, the greater the chance of a smoky fireplace. [Illustration: Figure 24.--Another good design is this revival of early New England architecture, which is frequently used for remodeling public dining rooms. The random-width pine planks were selected especially for variety in the pattern of the knots. Note the use of otherwise wasted space for bookshelves and closet.]