First things first. Are you a pipe sch. System or a hyd. Calculated system?
For pipe sch. See 8.15.19.4 and Hyd. Cal. System see 8.15.19.5


8.15.19.5 Revamping of Hydraulic Design Systems.
8.15.19.5.1 When hydraulically designed systems are revamped,
any existing bushing shall be removed and a nipple
not exceeding 4 in. (100 mm) in length shall be permitted to
be installed in the branch line fitting.
8.15.19.5.2 Calculations shall be provided to verify that the
system design flow rate will be achieved.
8.15.19.5.3 When it is necessary to pipe two new ceiling sprinklers
from an existing outlet in an overhead system, any bushings
shall be removed and the use of a nipple not exceeding 4 in.
(100 mm) in length and of the same pipe thread size as the existing
outlet shall be permitted, provided that a hydraulic calculation
verifies that the design flow rate will be achieved.
8.15.19.5.4 The use of pipe nipples less than 1 in. (25 mm) in
diameter is not permitted in areas subject to earthquakes.

If I remove all bushings (If there are any.) and the outlet is less than 1"
then I can use the outlet, 1/2" or 3/4" as is with up to a 4" nipple of the
outlet size, if the cal. Proves out. 

Thom McMahon, SET
Firetech, Inc.
2560 Copper Ridge Dr
P.O. Box 882136
Steamboat Springs, CO 80488
Tel:  970-879-7952
Fax: 970-879-7926



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