can only be selected by the careful judgment of the engineer. The chief points to be considered are efficiency of heating surface and capacity of grate in proportion to surface, strength of parts, tightness of joints, ease of cleaning and effectiveness of circulation—there should be no "dead ends" where the water is not kept in circulation by the heat of the fire.
| Willett's Table of Cast-iron Boiler Capacities. | |||
| Radiators; | Area of boiler | Radiators; | Area of boiler |
| total sq. ft. | grate in sq. in. | total sq. ft. | grate in sq. in. |
| 400 | 500 | 1,600 | 1,420 |
| 500 | 580 | 1,800 | 1,560 |
| 600 | 650 | 2,000 | 1,700 |
| 700 | 740 | 2,250 | 1,880 |
| 800 | 820 | 2,500 | 2,020 |
| 900 | 890 | 2,750 | 2,230 |
| 1,000 | 970 | 3,000 | 2,400 |
| 1,200 | 1,120 | 3,500 | 2,770 |
| 1,400 | 1,270 | 4,000 | 3,120 |
Fig. 9Fig. 10Fig. 11
One, Two and Three Column Radiators.
There might also be classed under the head of steam-heating apparatus the various traps, automatic receivers and other special appliances which are used especially in connection with exhaust heating for returning the water of condensation to the boiler, and which were described in the preceding chapter. But besides these the only apparatus pertaining to a heating system without
