The great thing about Outdoor Reset is that it is easy to implement. A small outdoor temperature sensor is placed on the exterior of the building and wired to the boiler control. Today's modern green boilers use advanced controls that can read the outdoor temperature and adjust the temperature of the boiler system water by using an outdoor reset curve that is set by the installer.
Outdoor Reset maximizes the effectiveness of a modulating boiler. Modulating boilers have variable outputs rather than traditional on-off boilers which do not have adjustable fire rates. you can think of Modulation as the adjustment knob on your stove. Modulation allows the boiler to run between "warm" and "high fire". By modulating the firing rate down, the boiler is able to run longer and actually runs more efficiently at lower firing rates.