Page 853 - 2018_IRC

APPENDIX A

A.6.2 Example 2: Hybrid or dual pressure systems. Deter- (4) Section A [2 psi (13.8 kPa) zone]
mine the required CSST size of each section of the piping (a) Distance from meter to regulator = 100 feet (30
system shown in Figure A.6.2, with a designated pressure 480 mm).
drop of 1 psi (6.9 kPa) for the 2 psi (13.8 kPa) section and 3- 3
inch w.c. (0.75 kPa) pressure drop for the 13-inch w.c. (2.49 (b) Total load supplied by A = 110 cfh (3.11 m /
kPa) section. The gas to be used has 0.60 specific gravity and hr) (furnace + water heater + dryer).
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a heating value of 1,000 Btu/ft (37.5 MJ/ m ). (c) Table 402.4(18) shows that EHD size 18
should be used.
Solution:
(1) Size 2 psi (13.8 kPa) line using Table 402.4(18). Note: It is not unusual to oversize the supply
line by 25 to 50 percent of the as-installed load.
(2) Size 10-inch w.c. (2.5 kPa) lines using Table EHD size 18 has a capacity of 189 cfh (5.35
402.4(16). m /hr).
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(3) Using the following, determine if sizing tables can be (5) Section B (low pressure zone)
used. (a) Distance from regulator to furnace is 15 feet
(a) Total gas load shown in Figure A.6.2 equals (4572 mm).
110 cfh (3.11 m /hr).
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(b) Load is 60 cfh (1.70 m /hr).
(c) Table 402.4(16) shows that EHD size 13
should be used.
Outlet D (6) Section C (low pressure zone)
furnace
Outlet C 100,000 Btu/h (a) Distance from regulator to water heater is 10
4 gal. automatic feet (3048 mm).
water heater
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35,000 Btu/h (b) Load is 30 cfh (0.85 m /hr).
Section 2
20 ft. (c) Table 402.4(16) shows that EHD size 13
should be used.
Section 1
Section 3 (7) Section D (low pressure zone)
20 ft. 10 ft. 15 ft.
(a) Distance from regulator to dryer is 25 feet
(7620 mm).
5 ft.
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10 ft. (b) Load is 20 cfh (0.57 m /hr).
15 ft. Outlet A (c) Table 402.4(16) shows that EHD size 13
Point of clothes dryer should be used.
delivery 35,000 Btu/h
Outlet B
range/oven unit
75,000 Btu/h
FIGURE A.6.1
PIPING PLAN SHOWING A STEEL PIPING SYSTEM

(b) Determine pressure drop across regulator [see
notes in Table 402.4(18)].
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(c) If pressure drop across regulator exceeds / 4
psig (5.2 kPa), Table 402.4(18) cannot be used.
Note: If pressure drop exceeds / psi (5.2 kPa),
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then a larger regulator must be selected or an
alternative sizing method must be used.
(d) Pressure drop across the line regulator [for 110
cfh (3.11 m /hr)] is 4-inch w.c. (0.99 kPa) based
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on manufacturer’s performance data.
(e) Assume the CSST manufacturer has tubing
sizes or EHDs of 13, 18, 23 and 30.

FIGURE A.6.2
PIPING PLAN SHOWING A CSST SYSTEM

828 2018 INTERNATIONAL RESIDENTIAL CODE ®
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