When a building design includes a large number of individual spaces such as apartments or offices, developers are always on the lookout for ways to reduce construction costs. There will always be a project expense for supplying hot water to a large number of units, but the installation and on-going costs can be minimised with the appropriate choice of heating system.

The main options for supplying hot water to apartments in medium or high-density developments are a centralised gas-fired water heating system or instantaneous heating systems installed at, or very near, the point of use. In a centralised system, large boilers and storage tanks are installed along with pipework to the apartments. Where a development has several hundred apartments, centralised hot water systems require multiple boilers and all pipework must be duplicated for the hot and cold supply. Each floor also requires two sets of pressure balancing valves. The hot water pipes to each apartment are often referred to as 'dead-legs', meaning that the water often cools down while waiting to be drawn off.

Such systems also present a more expensive initial cost for a property developer, given the requirements for a dedicated plant room, large commercial gas boilers, hot water storage tanks, circulating pumps, and the reticulation pipe work. These systems are often associated with higher maintenance costs. The alternative to a centralised system is 'instantaneous' heating at the point of use through Stiebel Eltron DEL units. In most cases a cold water feed is run to each apartment/space and a water heater installed so that the length of any 'dead leg' is significantly minimised.

There are many advantages in choosing stand-alone instantaneous hot water units:

1. Water is only heated at the time of use and energy is not wasted in maintaining a stored volume of hot water. 
2. With the heating units located closer to the point-of-use, pipe runs are shorter and less water is wasted by the user while waiting for hot water to arrive at the outlet. 
3. If only a cold-water feed has to be provided, the commissioning engineer only needs to configure the pressure balance once on each floor using pressure valves and pumps. The cold water feed can be run to each apartment and then connected to the water heater.

The Stiebel Eltron DEL electric instantaneous water heater provides a new approach to providing hot water supply in multi-level properties.