My boiler has a 1GPH 60 Degree SS nozzle. There's no nameplate anywhere but each service tag uses this nozzle. I adjusted for trace/zero smoke and I can't get the CO2 any higher than 5%. Draft is perfect (-04 & -02). Flue temp is 460 F. Unit is original (30 years old?).
Is ther anything I can do to get more efficiency?