For a low hazard boiler system that does not require chemical additives but has the potential to cause back pressure, what minimum backflow protection is necessary?

In a low hazard boiler system that doesn't require chemical additives but has the potential to cause back pressure, a double check valve with intermediate vent serves as the minimum backflow protection necessary. This is because the double check valve is designed to prevent any backflow that could occur due to positive pressure conditions in the system, while the intermediate vent allows for the release of air and minimizes the risk of siphoning and backpressure scenarios that could contaminate the potable water supply.

This protection is important in ensuring that any water potentially pushed back into the supply remains safe, as it effectively stops any potential cross-connection contamination that can arise from backflow. The other options either do not offer sufficient protection against back pressure or are not suitable for this particular type of application. For instance, a single check valve does not provide enough security against back pressure and back siphonage, thus failing to meet the necessary safety standards. Air gap separation, while effective, is typically not practical in all situations and may not be necessary for low hazard systems where double check valves can adequately perform the required function.