How Come???

STEVEN MARKS

Dan read the book but still have questions. On page 26 their is a picture with a boiler and by-pass piping. The caption below calls this system a boiler by-pass. It seems to me that this is actually a system by-pass because not all the water is flowing thru the radiators only a portion. All the circulated water is flowing thru the boiler. To me a boiler by-pass would be all the water flowing thru the system and only a portion flowing thru the boiler.
Am I still confused?
Which is best for a gravity conversion?
When would you use either one??
Thanks Still learning

Mike T., Swampeast MO

Don't have my copy in front of me, but will say that the terms "system bypass" and "boiler bypass" are confusing as you can kind of use either name for both depending on your perspective...

In a gravity conversion with a traditional boiler, you want to send some of the hottest supply water right back to the boiler return. This allows the boiler to come up to a reasonable operating temperature with reasonable speed. As long as the boiler isn't atrociously oversized and the thermostat anticipator is properly adjusted, you can bring the return temp up above the "condensing danger" zone in most weather.

With a cast iron boiler and a gravity conversion, problems from condensation seem to be easy in theory, but very difficult in practice--even with full outdoor reset and little or no bypass. Unfortunately, boiler efficiency takes a big hit so the gain you think you make by lowering the boiler temperature is lost. The less cold the weather and the shorter the boiler burn times, the greater the reduction in efficiency.