Weil-McLain Gold GV, adjust outlet temp


I posted this over in hvac, but I just get the 'you fool' answer. I am quite ready to accept, 'don't touch' but I'd like a bit of an explaination. Call me curious.
Just had a new (replacement) Weil-McLain Gold GV series 4 boiler installed. This unit heats fluid that is piped thru a basement floor.
The old unit, that rusted out (15 years old), had a lower outlet temperature. That unit supplied fluid at about 120F into the floor. This new unit is up around 140F. The old unit was installed by a professional and I never touched it.
I assume that the oulet temperature, at 140F, is related directly to the boiler inlet temperature; it's the same circuit. I'm guessing..
I don't have a schematic. My desire to reduce this temperature is based on increasing the boiler efficiency.
The user's manual says that the GCM (the units controller) mixes return water (cooled by the floor) and by-passed boiler output to maintain 140F temperature into the boiler sections, "to guard against condensation even if the return water is as low as 60F". Fluid returned from the floor is around 60F.
My questions are these.
Can the boiler inlet temperature be adjusted?
Would it be more efficient to lower the boiler inlet temperature?
Would lowering the temperature to, say, 120 be a good idea?
What is the reason to avoid condensation? Doesn't the condensate just flow into a drain?
And .....
I thought these new high eff boilers were being made with stainless. If that's the case, why would they worry about rusting?
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061218 0630 - werwer posted:

Yes, don't ask anything over in Faggotsville. They have their own little clique over there and don't want to be bothered with "HomeMoaner" queries...
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99.5 % of hvac people are crooks as you have just seen. Their work is not rocket science and most of them have an IQ of less than 50.

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