Can two Reznor UDXC300 unit heaters be common vented through a 10" B-vent?

Hello, thank you for reaching out. According to Reznor's UDXC installation manual, it states that UDXC300's cannot be common vented into a 10" B vent. Only UDXC unit sizes 30-100 may use a Category I common vent. If you have additional questions, please feel free to reach out over the phone to our Customer Service line at 1-888-901-5460. Have a great rest of your day.