Seasonal effects on hot-water heating systems flow temperatures.
Seasonal effects - outside temperature - and operating boiler temperatures in typical two-pipe forced hot water systems are indicated in the table below:
It is common to design a hot-water heating system for a temperature drop of 20 o C (36 o F ) in heating elements and radiators at what is considered as minimum outside design temperatures.
Maximum boiler flow temperature is often set to 80 o C (176 o F ) to avoid "burned dust" and accidentally injures on people when touching heaters. Outside design temperature depends on the actual location.
Hot Water Heating Systems - Flow Temperatures vs. Outside Temperatures
The Engineering ToolBox (2003). Hot Water Heating Systems - Flow Temperatures vs. Outside Temperatures. [online] Available at: https://www.engineeringtoolbox.com/flow-temperatures-heating-systems-d_190.html [Accessed Day Month Year].