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Posted by Heatpro on December 17, 2005 at 01:36:37:
In Reply to: Oversized boiler - Replace or not to replace? posted by GWR on December 17, 2005 at 00:14:13:
You won't be replacing a SYSTEM anytime soon, I imagine. You might replace the BOILER; but not the whole SYSTEM. I don't think it is necessary for you to replace the boiler, if you make sure you have the right piping and controls. The outdoor reset sensor can be put on the main loop to modify the water from 80F to 140F. The six-year-old boiler should already have a factory damper installed, or it isn't 80% AFUE.
An immediate problem you will have from your insulating is that you now require less than half the output, which will translate as not needing more than 140F water from your radiators during the coldest weather; they simply won't get hot because the thermostat will shut them off. The water will only need to average 100F over the year. This can make condensation problems for the boiler.
If you don't already have the boiler piped into the system as a loop-subloop configuration, now is the time to to it so the boiler can run at least 150F while the system runs at the lower temperatures it requires. The boiler pump will be as small as possible to allow the boiler to be hot while the system with its own circulator(s) is cold. It will require careful set-up.
The alternative is to remove the existing boiler and install Weil's new Phd condensing boiler.