Wall electric boilers have one heating circuit and are designed to heat the coolant in batteries or warm floors. Using the boiler, you can prepare water for the DHW system by connecting an indirect heating boiler. The issue of expediency here is quite seriously, because you can mount such a system, and it will work successfully, but it will be unnecessary costs. Why do this if you can install a separate electric boiler? It is better to let two independent electrical appliances be, so that in case of failure of the boiler, you do not be left without hot water.