Which configuration should be used for an instantaneous water heater when rapid scale deposits are possible?

The straight-tube, floating head exchanger is the appropriate choice for an instantaneous water heater in situations where rapid scale deposits are a concern. This configuration allows for easy cleaning and maintenance due to its design, which significantly aids in the removal of scale and other deposits that can accumulate over time.

In a straight-tube exchanger, the flow rate can be adjusted, which can help in managing the temperature differential and ultimately reducing the likelihood of scaling. Furthermore, the floating head design permits thermal expansion and contraction without imposing stress on the structure, making it more resilient in environments where scaling and fouling are prevalent.

Choosing this configuration ensures better performance and longevity of the water heater in settings where water quality issues, like high mineral content contributing to scaling, are likely to occur.