Instant Water Heaters: How They Work

Short: Instant water heaters heat water only at the moment it’s drawn, rather than constantly keeping a supply hot like a boiler. This means no standby losses, but they require high instantaneous power.

In more detail: The colder the incoming water and the higher the desired target temperature, the more power the unit must deliver on short notice.

In detail

• Electronic instant heaters: These devices regulate temperature precisely via flow rate and are today’s standard for new installations.
• Hydraulic instant heaters: Older, simpler models switch on purely through water pressure and offer less temperature comfort.
• High power demand: Since water must be heated instantly, instant heaters often need 18 to 27 kilowatts, requiring correspondingly strong house wiring.
• No standby losses: Unlike boilers, no energy is lost from constantly keeping a water supply warm.
• Limited flow rate: If multiple taps are used simultaneously, hot water temperature can drop since power output is limited.
• Decentralized installation: Small instant heaters directly at individual taps avoid long pipe runs and the associated heat loss.
• Maintenance and descaling: The harder the water, the more important regular descaling becomes, to avoid power loss and damage to the heating element (kaffeemaschine-und-wasserkocher-funktionsweise, waermepumpe).