The relief valve for a residential low-pressure hot water boiler system should be?

The relief valve for a residential low-pressure hot water boiler system is designed to open at a specific pressure to protect the system from dangerous overpressure conditions. The correct choice of 30 psig indicates that the relief valve is set to open at 30 pounds per square inch gauge, which is the standard pressure setting for many residential low-pressure hot water boilers. The term "gauge pressure" signifies that the measurement does not account for atmospheric pressure, making it suitable for systems that operate under atmospheric conditions.

In residential applications, using a relief valve set at 30 psig is effective in preventing overpressure that could lead to equipment failure or safety hazards. It represents a common standard in the industry for low-pressure boilers, ensuring safety while accommodating typical operational pressures.

Other options like 14.7 psia and 15 psia represent absolute pressure readings, which include atmospheric pressure. These values do not apply well to boiler systems, which typically operate using gauge pressure standards rather than absolute pressure. The choice of 30 psia is also incorrect as it reflects a reading that would be significantly outside the normal operational range for a low-pressure hot water system, as that would translate to over 59 psig when considering atmospheric pressure, thus exceeding safe design limits for