Stand-alone appliances for instantaneously heating water for Domestic Hot Water are known in North America as tankless heaters, elsewhere as multi-point heaters, or old brand names such as, geysers or Ascots. A common arrangement where hot-water supply and space heating is employed is for the boiler to combine hot-water and space heating production into one small cased unit. The combination boiler or combi for short. A combi heats a hydronic heating system and when Domestic Hot Water is called for all the power of the boiler is diverted to only supplying Domestic Hot Water.
Although instantaneous heaters can give a continuous supply of Domestic Hot Water the rate at which they can produce it is limited by the thermodynamics of heating water from the available fuel supplies.
Many tankless hot water systems avaliable today require special installation techniques. Ventting, Gas and Electric systems are a lot differend than standard storage tank units. When Inspectin this type of unit it is important to have a copy of the installation guide on hand. If you don't have one you can usally find them online.
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