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Public Health
Seattle & King County
401 5th Ave., Suite 1300
Seattle, WA 98104
Phone: 206-296-4600
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Public Health Plumbing Program
Installing Gas Piping
» Instructions for creating a printer-friendly version of this page.
| 1. |
Determine proper size: |
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Proper sizing of the pipe is important so that each gas appliance receives enough gas to perform properly. Each appliance has a minimum input demand in BTUs per hour. The chart below gives some examples of typical BTU demands. Look at the chart on the back of this insert to assist you in determining the proper pipe size for your job. To convert from BTUs to cubic feet per hour divide BTU by 1100 (example: 50,000 BTU by 1100 = 45.45 cubic feet of gas per hour). See the example on the back of this insert to help further illustrate this. To get BTU from cubic feet, multiply cubic x feet 1100 (45.45 cubic feet x 1100 = 50,000 BTU.)
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| 2. |
Approved gas piping fitting materials: |
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Approved materials are: wrought iron or steel (galvanized or black), corrugated stainless steel tubing or other approved materials. Ask your inspector if there are other materials you can use.
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| 3. |
Cutting pipe: |
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If you are cutting wrought iron or steel pipe, you must ream the cut of your pipe so you maintain the full inside diameter of the pipe.
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| 4. |
Special instructions: |
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Do not use ground joint unions except directly at the meter or after the shutoff valve at the appliance. Each place where you will have a gas appliance must have a gas cock in the open position, capped off. You are required to provide a test of the system for the inspector. Within the City of Seattle only, any person who installs gas piping on property not under their ownership must possess a Seattle Gas Piping Mechanic License. All gas piping installations require a permit and inspection.
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| 5. |
Testing: |
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Testing the system is your responsibility. The inspector does not perform the test or provide any of the equipment necessary for the test, including test gauges. Testing shall be as follows:
Within the City of Seattle, the typical low pressure systems shall be tested at 15 pounds per square inch (psi) using a 30 psi gauge. The test shall hold for at least 15 minutes without a perceptible drop in pressure. The system shall be under test at the time of inspection.
Within unincorporated King County, the test pressure to be used shall not be less than 1-1/2 times the proposed maximum working pressure, but not less than 3 psi. The test gauge shall have a range such that the highest end of the scale is not greater than 5 times the test pressure. (Typical low pressure tests would be 3 psi test using a 15 psi, 5 psi test using a 25 psi gauge, etc.) The test duration shall not be less than 10 minutes without a perceptible drop in pressure. The system shall be under test at the time of inspection.
If there is a drop in pressure, check for leaks. Check for leaks by filling a spray bottle with soapy water and spraying the solution on the pipe, where it meets the fittings. Bubbles show a leak and you should repair it appropriately. Continue this process until you have no leaks. Do not use an open flame to test for leaks.
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| 6. |
Inspection: |
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At the time of inspection, be sure to leave all of the gas piping exposed so the inspector can look at the whole system.
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Minimum Demand of Typical Gas Appliances in BTUs Per Hour
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Appliance
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Demand in BTU/hour
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| Barbecue (residential) |
40,000
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| Domestic clothes dryer |
35,000
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| Domestic Gas Range |
65,000
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| Domestic Recessed Oven Section |
25,000
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| Fireplace Gas Log |
80,000
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| Gas Refrigerator |
3,000
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| Storage Water Heater, 30-40 gallon tank |
35,000
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| Storage Water Heater, 50 gallon tank |
50,000
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> Example:
Problem: Determine the required pipe size of each section and outlet of the piping system shown.
> Solution:
| 1. |
Maximum gas demand of outlet A - 35,000 BTU per hour/1100 BTU per cubic foot = 31.82 cubic feet per hour.
Maximum gas demand of outlet B-3,000 BTU per hour/1100 BTU per cubic foot = 2.73 cubic feet per hour.
Maximum gas demand of outlet C-65,000 BTU per hour/1100 BTU per cubic foot = 59.09 cubic feet per hour.
Maximum gas demand of outlet D-150,000 BTU per hour/1100 BTU per cubic foot = 136.36 cubic feet per hour.
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| 2. |
The length of pipe from the gas meter to the most remote outlet (outlet A) is 60 feet.
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| 3. |
Using the column marked 60 feet on the size of gas pipe charge:
Outlet A, supplying 31.82 cubic feet per hour, requires one-half inch pipe.
- Section 1, supplying outlets A and B, or 34.55 cubic feet per hour requires one-half inch pipe.
- Section 2, supplying outlet A, B and C, or 93.64 cubic feet per hour requires three-quarter inch pipe. Section 3, supplying outlets A, B, C, and D, or 230 cubic feet per hour, requires one-inch pipe.
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| 4. |
Using the column market 60 feet: Outlet B supplying 2.73 cubic feet per hour requires one-half inch pipe. Outlet C, supplying 59.09 cubic feet per hour, requires one-half inch pipe.
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| 5. |
Using the column marked 50 feet: Outlet D, supplying 136.36 cubic feet per hour, requires three-quarter inch pipe. |
> Size of gas piping
- Gas type is natural gas.
- The inlet pressure is 0.5 psi or less.
- The allowable pressure drop is 0.5 inches water column.
- The specific gravity of the gas being supplied is 0.60.
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Length in feet
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Pipe size
(inches)
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10
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20
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30
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40
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50
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60
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70
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80
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90
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100
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125
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1/2
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175
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120
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97
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82
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73
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66
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61
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57
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53
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50
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44
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3/4
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360
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250
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200
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170
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151
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138
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125
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118
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110
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103
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93
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1
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680
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465
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375
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320
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285
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260
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240
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220
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205
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195
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175
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1-1/4
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1,400
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950
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770
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660
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580
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530
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490
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460
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430
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400
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360
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1-1/2
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2,100
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1,460
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1,180
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990
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900
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810
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750
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690
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650
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620
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550
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2
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3,950
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2,750
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2,200
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1,900
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1,680
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1,520
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1,400
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1,300
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1,220
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1,150
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1,020
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2-1/2
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6,300
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4,350
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3,520
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3,000
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2,650
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2,400
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2,250
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2,050
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1,950
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1,850
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1,650
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3
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11,000
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7,700
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6,250
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5,300
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4,750
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4,300
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3,900
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3,700
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3,450
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3,250
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2,950
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