Combustion Air Supply and Ventilation

Table 1

Natural Gas Pipe Capacity Table (Cu. Ft./Hr.)

Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific gravity of 0.60 (natural gas).

Nominal Iron Pipe

 

 

 

Length of Pipe, Feet

 

Size, in. 10

20

30

40

50

60

70

80

90 100 125 150 175 200

1/2

132

92

73

63

56

3/4

278

190

152

130

115

1

520

350

285

245

215

1-1/4

1050

730

590

500

440

1-1/2

1600

1100

890

760

670

 

 

 

 

 

 

50

46

43

40

38

34

31

28

26

105

96

90

84

79

72

64

59

55

195

180

170

160

150

130

120

110

100

400

370

350

320

305

275

250

225

210

610

560

530

490

460

410

380

350

320

 

 

 

 

 

 

 

 

 

After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour required for the gas input rating of the water heater. By formula:

Cu. Ft. Per Hr. Required= Gas Input of Water Heater (BTU/HR)

Heating Value of Gas (BTU/FT³)

The gas input of the water heater is marked on the water heater data plate. The heating value of the gas (BTU/FT3) may be determined by consulting the local natural gas utility.

Additional tables are available in the latest edition of the "National Fuel Gas Code", ANSI Z223.1.

Combustion Air Supply and Ventilation

Manual backgroundWARNING

Carbon Monoxide Warning

Follow all the local and state codes or, in the absence of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1 (NFPA 54)- latest edition to properly install vent system.

Failure to do so can result in death, explosion, or carbon monoxide poisoning.

IMPORTANT: Air for combustion and ventilation must not come from a corrosive atmosphere. Any failure due to corrosive elements in the atmosphere is excluded from warranty coverage.

The following types of installation (not limited to the following) will require outdoor air for combustion due to chemical exposure and may reduce but not eliminate the presence of corrosive chemicals in the air:

beauty shops

photo processing labs

buildings with indoor pools

water heaters installed in laundry, hobby, or craft rooms

water heaters installed near chemical storage areas

Combustion air must be free of acid-forming chemicals such as sulfur, fluorine, and chlorine. These elements are found in aerosol sprays, detergents, bleaches, cleaning solvents, air fresheners, paint, and varnish removers, refrigerants, and many other commercial and household products. When burned, vapors from these products form highly corrosive acid compounds. These products should not be stored or used near the water heater or air inlet.

Combustion and ventilation air requirements are determined by the location of the water heater. The water heater may be located in either an open (unconfined) area or in a confined area or small enclosure such as a closet or small room. Confined spaces are areas with less than 50 cubic feet for each 1,000 BTUH of the total input for all gas using appliances.

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