No hard-and-fast rules can be employed for determining the heating capacity of boilers or for ascertaining the sizes best adapted for different jobs. The following table is deduced from practical tests and observations by Prof. Carpenter, of Cornell University, and is considered to be within the limits of safety. Two cases are taken: (A) when the rate of coal consumption is 10 lb., and (B) when it is 8 lb. per sq. ft. of grate surface per hour. The latter is preferable for hot-water heating.

Proportioning Parts of Heating Boilers. - Steam Heaters.

Radiation by Feet.

250

500

750

1,000

1,500

2,000

3,000

4,000

5,000

7,500

10,000

Nominal horsepower .........

2.5

5

7.5

10

15

20

30

40

50

75

100

Radiating to heating surface

4.5

5.1

5.4

5.6

6

6.2

6.7

6.9

7|9*

7

9*

7

9*

Evaporation per lb. of coal

5.5

5.7

6

6.5

7

7.5

8

8.5

9

9.5

10

Lb.steam per sq. ft. grate A

55

57

60

65

70

75

80

85

90

95

100

Lb Steam per sq. ft. grate B

44

46

48

52

56

60

64

68

72

76

80

Radiating to grate surface A

165

171

180 195

210

225

240

256

270

285

300

Radiating to grate surface B

132

138

144 |156

168

180

192

204

216

228

240

ting to grate surface A

36.5

88.2

33.2

34.8

35

36.2

36.5

37.0

38.5

40.5

31.5*

42.5

88.8

Heating to grate surface B

28.5

27

27.7

27.7

28

29

28.5

20.6

30.8

32.7

25.6*

34.5

26.5*

Boiler Beating surface, sq.ft.

55

98

138

178

250

322

447

580

710

1071

833*

1430

1111*

Grate surface, sq. ft..........A

1.52

2.92

4.15

5.68

7.15

8.9

12.4

15.7

18.5

26.5

88.8

Grate surface, sq. ft...........B

1.88

8.88

5.4

6.37

8.92

11 .2

15.5

19.5

23.2

32.5

41.5

Diam. safety valve, in.....................

1.5

2.25

2.5

2.75

3

3.25

3.5

4

4

two 3-inch

two 4-inch

Diam. smoke pipe, in...........

7

10

11

12

15

17

19

23

25

28

34