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Engineering ToolBox > Flow Temperatures in Hot-Water Heating Systems
Seasonal operating boiler temperature of two-pipe forced hot water systems are indicated in the table below - for different minimum outside design temperatures.
It is common to design hot-water heating systems for temperature drops of 20oC in radiators and heating elements at minimum outside design temperatures. Maximum boiler flow temperatures are often set to 80 oC to avoid "burned dust" and accidentally injures by touching the heaters. The outside design temperature depends on the actual location.
| Boiler Flow Temperature (oC) | |||||
| Minimum Outside Design Temperature (oC) | Outside Temperature (oC) | ||||
| -20 | -10 | 0 | 10 | 20 | |
| -20 | 80 | 66 | 51 | 37 | 37 |
| -10 | 80 | 58 | 37 | 37 | |
| 0 | 80 | 37 | 37 | ||