What backflow prevention device is REQUIRED for the potable water supply to a boiler when there are no conditioning chemicals in the water supply

This device is primarily used in scenarios where a potential contamination risk exists, such as irrigation systems or chemical processes. Since the question specifies that there are no conditioning chemicals in the water supply, a backflow preventer with an intermediate atmospheric vent is not necessary and does not meet the requirements for this situation.

While this type of device is effective for protecting against backflow in high-hazard applications, it is not required when there are no conditioning chemicals present in the water supply. The double check-valve assembly is sufficient for low-hazard situations, making this option unnecessarily complex and costly for the given scenario.

A pressure-type vacuum breaker is used to protect against back siphonage but is not appropriate for a system where there is no risk of contamination from chemicals. Its design is more suitable for applications that involve potential contamination risks, which does not apply here.