page_title: Tankless water heating
section_title: Tankless heater controls
hierarchical_section_title: Tankless water heating / Tankless heater controls
caption_attribution_description: Deutsch: Hydraulisch gesteuerter Durchlauferhitzer, 2 kW Maximalleistung, Einphasenwechselstrom, 230 Volt Phasenspannung
context_page_description: Tankless water heaters—also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters are water heaters that instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil. Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication.
  Tankless heaters may be installed throughout a household at more than one point-of-use, far from a central water heater, or larger centralized models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a plentiful continuous flow of hot water, and potential energy savings under some conditions. The main disadvantage of these systems are their high initial costs.
context_section_description: Tankless water heaters can be further divided into two categories according to their heating capability: "full on/full off" versus "modulated". Full on/full off units do not have a variable power output level; the unit is either fully on or completely off. This can cause an annoying and possibly hazardous variation of hot water temperature as the flow of water through the heater varies.  Modulated tankless water heaters change their heat output in response to the flow rate of water running through the unit. This is usually done by using a flow sensor, a modulating gas valve, an inlet water temperature sensor, and an outlet water temperature sensor-choke valve. A properly configured modulating heater can supply the same output temperature of water at differing water flow rates within their rated capacity, usually maintaining a close range of ±2 °C.
  A high-efficiency condensing combination boiler provides both space heating and water heating, and is an increasingly popular choice in UK houses. In fact, combination boilers now account for over half of all the new domestic boilers installed in Britain.
  Under current North American conditions, the most cost-effective configuration from an operating viewpoint often is to install a central (tank-type or tankless) water heater for most of the house, and to install a POU tankless water heater at any distant faucets or bathrooms. However, the most economic design may vary according to the relative electricity, gas and water prices in the locality, the layout of the building, and how much (and when) hot water is used. Only electric tankless water heaters were widely available for many years. and they are still used for low-initial-cost POU heaters, but natural gas and propane POU heaters have now become available for consideration.
caption: Electric point-of-use (POU) tankless water heater, wall-mounted under a sink (Germany)
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