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Posted by HeatPro on December 08, 2008 at 22:30:56:
In Reply to: Manual modulation of oversized old boiler? posted by Michael_C on December 08, 2008 at 18:46:33:
The maximum efficiency is achieved at the factory with all the burners going. Reducing the fire by lowering gas pressures or shutting burners off allows bypass air to cool the exchanger to take some more of the heat up the chimney. The old boiler was less than 70% efficient as it was.
It is possible to block off a few passages and block the gas from the burners in that section; but it can subject the boiler to stress. It would produce less stress to remove 'extra' sections when possible to make the boiler a smaller unit with fewer burners.
To achieve greater efficiency, it is better to pump the heated water after the burner shuts off into another tank to make use of it for hot water or as a preheat for the next cycle. The system 2000 boilers make use of that technique.