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Posted by HeatPro on November 17, 2005 at 19:15:15:
In Reply to: circulator vs gravity posted by Daniel on November 17, 2005 at 00:56:48:
Whether you left the system as gravity or added a circulator, that large mass of water, cast-iron, and steel pipe still takes the same amount of energy to heat it up in 25 minutes. A circulator does not change the rate of boiler input, so putting a circulator in or not does not change the heat-up time.
Installing the bypass as suggested makes the system into a boiler subloop so the boiler can be protected by locally heating the water in the main so mixed water can re-enter the boiler to keep the temperature higher in the boiler out of the condensing range sooner.
Using an outdoor reset control would help regulate the burner so the water would become as hot as needed during particular outdoor temperatures. Gravity systems were invented for solid fuel systems where the fuel was lit constantly from fall to spring, not for on-off burners remotely controlled by a thermostat (there were no thermostats then, the people in the house regulated the flame size when they started becoming too cool.)
You can buy the biggest pump you can find to whiz water around the circle at high speed; but it won't make the boiler heat the water faster unless you up the burner input significantly (and that is not efficient or necessary.) Understanding how to control a system that has never needed a circulator is more useful.
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