Flow Temperatures in Hot-Water Heating Systems
Seasonal effects on flow temperatures in hot-water heating systems
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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 20 oC 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 | ||
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Related Topics
- Heating - Heating systems - capacity and design of boilers, pipelines, heat exchangers, expansion systems and more
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Related Documents
- Calculating Expansion Tanks - Calculating expansion volume in open, closed and diaphragm expansion tanks
- Flow Rates in Heating Systems - Calculating flow rates in heating systems
- Hot Water Heating Systems Design - An introduction to Gravity Heating Systems and Forced Heating Systems





