Can a boiler bypass save fuel?
Yes it can. When a boiler bypass is installed in a large water volume system the reduced flow through the boiler. Although all the water in the system needs to be heated the entire system does not have to be raised to 180f degrees. With reduced flow through the boiler the boiler can get above the condensing point of 140f. It will not be uncommon for the system temperature to be much lower than the boiler temperature. You may see the boiler getting 160f – 180f but the system water may only be 120f or 140f. The advantage of the boiler bypass is the system temperature gets warmer as it gets colder outside and gets cooler as the day warms up. With large water volume system (usually cast iron radiation) the system will operate at much lower water temperatures. See required water temperature for cast iron systems.
