A.O. Smith DB/DW-720-1810 warranty Purging, Correct GAS

PURGING

Gas line purging is required with new piping or systems in which air has entered.

CAUTION

PURGING SHOULD BE PERFORMED BY PERSONS EXPERIENCED IN THIS TYPE OF GAS SERVICE TO AVOID RISK OF FIRE OR EXPLOSION. PURGE DISCHARGE MUST NOT ENTER CONFINED AREAS OR SPACES WHERE IGNITION CAN OCCUR. THE AREA MUST BE WELL VENTILATED AND ALL SOURCES OF IGNITION MUST BE INACTIVATED OR REMOVED.

BEFORE PLACING THE BOILER IN OPERATION, CHECK FOR GAS LEAKAGE. Use soap and water solution or other material acceptable for the purpose in locating gas leaks. DO NOT USE MATCHES, CANDLES, FLAME OR OTHER SOURCES OF IGNITION FOR THIS PURPOSE.

1.CORRECT GAS

Make sure the gas on which the boiler will operate is the same as that specified on the boiler rating plate. Do not install the boiler if equipped for a different type gas, consult your gas supplier. These boilers are designed to operate on natural gas only.

2A. SIZING GAS SUPPLY LINE (For single boiler installations and for installations of multiples of two or three of same size boilers).

Use table 1, which is taken from ANSI booklet Z223.1, NATIONAL FUEL GAS CODE, and/or CAN/CSA-B149.1-00 to size iron pipe or equivalent gas supply line. Table 4 is based on a pressure drop of 0.3 inches of water and a specific gravity of 0.60 which is approximately for natural gas. (LP gas has an S.G. of about 1.53). If the service pressure is five inches water column or less, use one pipe size larger than specified in table 1 in order to minimize pressure drop in the line.

2B. SIZING GAS SUPPLY LINE (For multiples of over three boilers of same size or for multiple installations of two or more mixed sizes).

Capacities in cubic feet per hour of 0.60 specific gravity gas for different sizes and lengths are shown in table 4. No additional allowance is necessary for an ordinary number of fittings.

Where it is necessary to use more than the average number of pipe fittings i.e. elbows, tees, and valves in gas supply line, use a pipe larger than specified to compensate for increased pressure drop.

TABLE 4

MAXIMUM CAPACITY OF PIPE IN CUBIC FEET OF GAS PER HOUR (BASED UPON A PRESSURE DROP OF

0.3 INCH WATER COLUMN AND 0.6 SPECIFIC GRAVITY GAS)

Length in Feet (Meters)				Nominal Iron Pipe Size, Inches (NPT)
From Gas Meter	1/2	3/4	1	1 1/4	1 1/2	2	2 1/2	3	4
10 (3)	132	278	520	1,050	1,600	3,050	4,800	8,500	17,500
20 (6)	92	190	350	730	1,100	2,100	3,300	5,900	12,000
30 (9)	73	152	285	590	890	1,650	2,700	4,700	9,700
40 (12)	63	130	245	500	760	1,450	2,300	4,100	8,300
50 (15)	56	115	215	440	670	1,270	2,000	3,600	7,400
60 (18)	50	105	195	400	610	1,150	1,850	3,250	6,800
70 (21)	46	96	180	370	560	1,050	1,700	3,000	6,200
80 (24)	43	90	170	350	530	990	1,600	2,800	5,800
90 (27)	40	84	160	320	490	930	1,500	2,600	5,400
100 (30)	38	79	150	305	460	870	1,400	2,500	5,100
125 (38)	34	72	130	275	410	780	1,250	2,200	4,500
150 (46)	31	64	120	250	380	710	1,130	2,000	4,100
175 (53)	28	59	110	225	350	650	1,050	1,850	3,800
200 (61)	26	55	100	210	320	610	980	1,700	3,500

*The heating value of natural gas is approximately 1050 Btu/ft³. Propane (L.P.) gas has a heating value of approximately 2500 Btu/ft³.

TABLE 5

Multipliers To Be Used With Table 1 When Applying The

Gravity Factor To Other Than .60 Specific Gravity

	Specific			Specific
	Gravity	Multiplier	Gravity	Multiplier
.35		1.31	1.00	.78
.40		1.23	1.10	.74
	.45	1.16	1.20	.71
.50		1.10	1.30	.68
.55		1.04	1.40	.66
	*.60 (Nat.)	1.00	*1.50 (Prop.)	.63
.65		.96	1.60	.61
.70		.93	1.70	.59
.75		.90	1.80	.58
.80		.87	1.90	.56
.85		.84	*2.00 (Butane)	.55
.90		.82	2.10	.54

*Use these correction factors if exact specific gravity of the gas is not known.

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