Boilers that are connected to an outdoor reset control operate more efficiently. An outdoor reset lowers the boiler’s water temperature as the outdoor temperature rises, and usually features warm-weather-shutdown capability. The increase in efficiency is a result of the lower operating temperature. Especially useful during the "shoulder months" of the spring and fall, it leads to less heat loss and fewer boiler cycles. Room temperatures fluctuate less.
The analogy of city vs. highway driving is often cited in association with outdoor resets. The starting and stopping of city driving (along with its lower gas efficiency) compares to a boiler without an outdoor reset. A boiler with an outdoor reset, meanwhile, operates at a constant temperature with less starting and stopping. It runs more efficiently, like a car on the highway.
