Outdoor reset works hand-in-hand with modern modulating, condensing boilers to drive significant gains in energy efficiency. The principle is simple to understand, and easy to implement. The basic principle is that a hydronic heating system should operate at higher temperatures when it is colder outside. This allows the system to transfer more heat to the building and keep up with the increased heat loss due to the colder weather. The simple formula is Lower outdoor temperatures = Higher heat loss from the building = Higher hydronic temperatures to transfer more heat to the building.
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.