opslaggeiser

An opslaggeiser is a type of domestic water heater that stores hot water in an insulated tank for later use. In Dutch-speaking regions, the term distinguishes storage-type water heaters from door-stroom geisers, which heat water on demand.

Storage geisers typically use a tank sized to household needs, from tens to hundreds of litres. Heating methods include electric immersion heaters, gas burners, or integration with solar collectors or heat pumps. Tanks are usually lined with enamel or glass and well insulated to reduce standby losses.

Temperature is controlled by a thermostat, commonly set around 60°C to limit Legionella growth, with safety devices such as a thermal cutout and a mixing valve to prevent scalding. Regular maintenance—such as flushing sediment, checking anode protection, and inspecting the pressure relief valve—helps extend service life.

Advantages include immediate availability of hot water during peak demand and compatibility with energy-saving strategies like solar preheating or heat-pump systems. Disadvantages include standby heat loss, required storage space, and potential bacterial growth if not properly maintained.

Compared with instantaneous (on-demand) water heaters, opslaggeisers provide a stable supply of hot water at the cost of energy efficiency and space. They are common in households in the Netherlands and Belgium, with modern systems often incorporating hybrid or solar-assisted variants.