Does Economy 7 immersion heater need a timeswitch?


Postby Franship » Fri Dec 04, 2009 2:36 pm

Hi everyone,

I have a large dual element immersion heater which we only heat overnight via the Economy 7 switch. We keep the Eco 7 switch on all the time as it kicks in from about 11.30pm to about 6.30am.

Most of the energy used in our flat is overnight, which must be coming from the immersion and also in the winter months, one or two storage heaters.

I am wondering how much energy the immersion uses when it's left switched on after the tank has heated up. It must take about an hour to heat, so is it using up lots of energy being kept switched on for the remaining 6 hours?

I'm presuming that as Eco 7 timer switches are available, then it will save us energy if we have one installed to come on for just one hour overnight. But I've been given conflicting information saying the heater switches off after the tank reaches 60c.

Does anyone know the answer to this?!

Thanks.
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Postby plumbbob » Fri Dec 04, 2009 6:46 pm

All immersion elements need thermostats stop the water form continuing to heat until it boils. The thermostat as you say will switch the element off as soon as the setting is reached (normally 60 degrees). This means that if no water is drawn off during the day and the water temperature stays at 60 then the element will use no energy so it could remain on 24/7.

Now in reality, the tank will lose heat and of course hot water will be used during the day so the element will be switched on and off to replace this lost heat. Now the trouble is, as most water is used during the day this means the element will be on mostly during the day using the higher rate tariff. In fact, by 1am when the economy 7 tariff kicks in, the water will have already been heated because you are not using water at night and you won't be benefiting from the cheaper electricity!

To combat this,the main element is normally timed to go on and off with the E7 tariff and you should have the option of a boost button to operate the second element during the day if you run out of hot water.

Generally, if you have storage heaters this operation is automatic. If you simply have a two rate meter, you may need/have a timer to control the element.
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