Boiler on Gas
A boiler works with the principle that cold water is heavier than hot water: cold water is pumped at the bottom of the boiler and the heated water rises upwards, after which a circulation pump sends it through the house.
Indirect Fired Boiler
Hot water can also be prepared using the central heating boiler. This is done with a boiler in the vicinity of the boiler, separately placed, or one that is integrated in the central heating boiler, the so-called combi boiler. The boiler water from the boiler flows thorugh the heat exchanger of the boiler and thereby indirectly heats the water in the boiler. All this works according to the countercurrent principle whereby the hot water of the central heating system is pumped from top to bottom through a spiral-wound copper tube through the boiler. The cooled water is returned to the boiler where it is heated again; it circulates between the boilers.
An electric boiler heats the water through a heating element that is controlled by a thermostat. Advantages compared to gas boilers: electric boilers are smaller, require less maintenance, require no flue gas discharge and do not use oxygen. They can be placed wherever water and electricity is available. The disadvantage is the higher energy costs because electricity is more expensive than gas, although these costs can be reduced by making optimal use of the off-peak rate (with an installed double rate-meter). Further disadvantages are: the longer required warm-up time and that sometimes a three-phase connection is required, plus a separate group in the meter cupboard. In areas with hard water, limescale can form on the heating element, making it no longer efficient.
A solar boiler uses the heat radiation from the sunlight. Solar boilers are heated in the same way as an indirectly fired boiler, but the heating of the circulating water takes place in a solar collector.