Reading a current thread about turbulators and fire tube cleaning procedures got me to thinking about something completely different. Well, maybe not so different. Have any of you inquiring minds out there that have changed your boiler return temps, either by swapping out thermostatic units or tweaking pump or bypass valve settings, ever noticed or even suspected that it changed how quickly your heat exchangers got cruddy? This would require some careful control of several variables to test conclusively but I was just wondering. If 20 or 30 degrees could make a noticeable difference it could be another reason not to go too low on the return temps even though intuitively a lower return temperature would sound more efficient ( delta T and all that). I recall Jebatty saying that he feels he gets better efficiency with a slightly higher return temp than the minimum recommended 130F or so. Haven't thought about it a lot but wanted to post the question before it slipped my mind entirely.