An outdoor sensor and a reset curve set the target water temperature, for example 180 degrees F at the coldest design day sliding down to 110 at 55 degrees outside, with warm weather shutdown above that. Matching water temperature to heat loss gives longer, steadier burner cycles, more even comfort and, on condensing boilers, more time in the condensing range.
Outdoor reset curve's too steep, at 40 out it's sending 170 water and the zones overshoot every time.
Lower the curve a few degrees at a time until the coldest room just keeps up; that is the efficient setting.
Also heard as
- ODR
- reset
- weather compensation
Related terms
Condensing boiler
A boiler designed to cool flue gas below its dew point so water vapor condenses and gives up its latent heat.
Aquastat
Shop name for the immersion temperature control that fires and limits a hot water boiler.
Delta T
The temperature difference between supply and return water in a hydronic system.
Short cycling
A burner starting and stopping far too often, with short run times that waste fuel and wear parts.