What is a common usage challenge with instantaneous water heaters?

A common challenge with instantaneous water heaters is handling fluctuating water demands. These types of water heaters are designed to heat water on demand rather than store hot water, which allows for efficient energy use. However, when multiple fixtures are used simultaneously or when the demand varies significantly in a short time, the heater may struggle to keep up with the needed flow rate. This can lead to inconsistent water temperatures or insufficient hot water, especially if the heater is not equipped to handle the total flow required by the various outlets. For example, if someone starts a shower while a dishwasher is running, the instantaneous heater may not provide adequate hot water for both, resulting in cold water being delivered to one or both fixtures during peak usage.

This challenge is particularly relevant in residential settings where multiple bathrooms and appliances may be in use at the same time, making it crucial for the design of hot water systems to consider the potential for fluctuating demand in order to select appropriate equipment and sizing.