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Posted by HeatPro on November 16, 2010 at 21:09:50:
In Reply to: Differential Setting posted by Dan on November 16, 2010 at 19:57:46:
: I have an old steel boiler and is used for heating only--gas fired water boiler.
You don't need a low limit on a heating only steel (welded) boiler.
20 degrees is 'normal' if you want it, fixed differentials are often at 10F.
The differential is only there to make a lower setting for the burner to fire again after the boiler reaches the highest setting. A 20F differential is unnecessary for a gas burner and won't make a difference in efficiency.
When the burner is the right input to match the radiation output, and you don't have zones, the boiler temperature wouldn't reach the high limit unless there was a problem blocking water flow.