What is the normal operating temperature for a hot water heating system

What is the normal temperature of hot water?

Question has a range of answers, for example some one may say 40 C, some may say 50 C and so on. Water remains liquid up to about 100 C depending on the atmospheric pressure. Thus one may say that any thing between 40 C to 100 C would answer your question.If by “hot water” you mean boiling water, the boiling water temperature at sea level is 100 degrees centigrade. If by “hot water” you mean below the boiling point, in some countries heating is required when temperatures drop below 21 degrees centigrade, therefore “hot water” could be considered hot in the range of 21 to 99.9 degrees centigrade.