The Rheem RTGH-95DV ships with the Royal GVS pancake termination. This cannot be installed on IPEX 636 venting. The IPEX 636 pancake termination part numbers are listed here,
PN 196984 - 2" IPEX Pancake Style - vent termination kit
PN 196985 - 3" IPEX Pancake Style - vent termination kit
Update: Following UL Bulletin 2009-18, it has been decided that the Royal termination can be used on IPEX 636 venting.
Download UL Bulletin 2009-18 - Here (http://www.hvactechgroup.com/files/UL2009-18.pdf)
QuoteVent Terminations - Clause 4.7 F does not apply to unique, non-metallic vent terminations supplied by the appliance manufacturer provided the vent terminations comply with ULC-S636 and is compatible with vent systems specified by the appliance manufacturer.