Water heaters with a double wall used primarily manufacturers in order to get rid of the shortcomings of the Tankless water heater of the first type. Indeed, the heat exchange surface of the device in 2,0-2,5 times higher than the surface of the coil, partially solved it and the problem of scaling. This design uses a Japan company (Takagi), a well-known manufacturers to replenish line coil Tankless water heaters (Carbofuel, Viessmann).
* Their pluses: Increased rate of radiant heating water
* Slow scale deposit
* Their disadvantages: Technological complexity
* The possibility of bacteria in stagnant zones
* Low prevalence of construction