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How powerful are electric instantaneous boilers?

Instantaneous Heaters

How powerful are electric instantaneous boilers? Well Electric Instantaneous heaters go from single phase electricity to three phase electricity. The single-phase electricity starting at 2.8kW the ES3 and goes to 11kW for the DEX12. With the Three phase, instantaneous heaters they start at 18kW with the DBX18 and go all the way up to 27kW with the DBX27. It is suggested that what the heater is heating is no further than 2 metres otherwise the flow rate will be affected.


With the single phase, it starts with the ES3 which has got a kW rating of 2.8kW. With a supply of 230V and an incoming water temperature of 12 degrees. Then this would have a flow rate of 1.5 litres per minute so this is ideal for a wash hand basin. There are 3 heaters in the ES range which also includes the ES4 and ES6. These have flow rates of 2.4 and 3.0 litres/min respectively, so they would be able to do a wash hand basin or a kitchen sink. 

Another popular range of instantaneous heaters is the CEX range. This comes in 2 models the over sink and the under sink, upon installation it can be set at either 8.8kW or 6.6kW. Set at 6.6kW then it would have a flow rate of 3.6 litres/minute. This would be enough for a basin or kitchen sink. When set at 8.8kW then this would be able to cope with a shower and the flow rate would be 4.8 litres/minute.


The last single phase instantaneous heater that Zip do is the DEX12. Like the CEX range this also can be set at different kW ratings, either 8.8 or 11kW. At 11kW this has got a flow rate of over 5 litres/min. Zip say that this would be powerful enough to cope with a bath. However, it would take around 20-25 minutes to fill it to the required temperature.

If you have the electrical capability to have three phase electricity, then you can go up to 27kW which is very powerful. However, not many building have the capability of having three phase electricity as this is mainly only found in commercial properties.

Table on the different flow rates and kW rating of the single phase heaters: