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Posted by HeatPro on November 01, 2009 at 10:21:35:
In Reply to: Re: Removing section of cast iron boiler to lower BTU output posted by NHMatt on October 31, 2009 at 19:59:47:
You can keep a high enough stack temperature by keeping the boiler water hot with a low limit. You would gain some efficiency if the boiler is downfired, maybe enough to condense on the passages during the long warm-up on each firing demand. A hot boiler would avoid such problems, though it would lose some efficiency. It could balance out with a benefit of less expansion and contraction and no condensation.
After trying that, you would still have the same boiler and burner, so if a problem go on to removing the section.
If you remove the section first, and change the burner internals, and it doesn't work out as well, it is double work to go back and try it.
You can still use the boiler as is for a while to see how it cycles. Having a 140,000 boiler when a 100,000 boiler is required was more a usual situation for half a century; but that's why the estimates were supposed to be done better.
If you are trying to have your cake and eat it too, (get the wrong boiler for your needs and estimate, then modify it to get the same efficiency,) you're better off getting the right size boiler that was designed for it at the factory and take the warranty, which you won't have if you modify it.