To ensure efficient heat distribution in a hot water system, the difference between boiler supply temperature and return temperature must not be less than how many degrees?

To ensure efficient heat distribution in a hot water system, the difference between boiler supply temperature and return temperature must not be less than how many degrees?

• A. 10
• B. 20
• C. 30
• D. 5

Answer: (B)

In a hot water system, the water leaves the boiler hot (supply) and returns cooler after releasing heat to the radiators or radiant loops. The difference between these two temperatures, the delta-T, is the driving force for heat transfer through the system. If that delta-T is too small, not enough heat is being delivered per pass—return water stays relatively warm, heat distribution becomes inefficient, and the boiler can end up cycling more or wasting energy. A minimum delta-T of about 20°F (roughly 11°C) provides enough temperature drop across the emitters to ensure effective heat transfer and efficient boiler operation. If the delta-T falls below this, you’d see poorer heat distribution and reduced efficiency.

In a hot water system, the water leaves the boiler hot (supply) and returns cooler after releasing heat to the radiators or radiant loops. The difference between these two temperatures, the delta-T, is the driving force for heat transfer through the system. If that delta-T is too small, not enough heat is being delivered per pass—return water stays relatively warm, heat distribution becomes inefficient, and the boiler can end up cycling more or wasting energy. A minimum delta-T of about 20°F (roughly 11°C) provides enough temperature drop across the emitters to ensure effective heat transfer and efficient boiler operation. If the delta-T falls below this, you’d see poorer heat distribution and reduced efficiency.