The relief valve for a low pressure hot water system should be set at:

The relief valve for a low pressure hot water system should be set at 30 psig because this setting is crucial for ensuring the safety and proper functioning of the system. A relief valve is designed to prevent excessive pressure build-up within the system, which can lead to dangerous conditions such as pipe rupture or equipment failure.

In the context of low pressure hot water systems, a setting of 30 psig provides a suitable threshold that balances operational efficiency with safety measures. This level is commonly accepted within industry standards to accommodate the operating pressures of typical low pressure hot water applications while still engaging safety mechanisms when necessary.

It's important to clarify that settings like 14.7 psia or 30 psia do not apply effectively to low pressure systems since they do not reflect the typical gauge pressure range required. Gauge pressure accounts for atmospheric pressure, which is typically around 14.7 psi, so using psia would be inappropriate in this context, as it doesn't provide a true indication of the pressure relative to atmospheric levels.