Economy 7 - Help!

DJ_MPH

Hi Guys,

Firstly, Happy New Year to you all!

I could really do with some more input on this please?

Would also appreciate it if someone knows roughly how many kwh on average economy 7 water heaters/boilers use.

Thanks

macman

Per hour, they'll use whatever the rating plate on the device shows. So a 2kW storage heater will use 2kWh per hour.
If by boiler you mean an immersion heater, the same applies, assuming that the thermostat does not cut in during the 'on' period.
There is no average, as devices vary greatly in size and output.

HappyMJ

DJ_MPH wrote: »

Hi Guys,

Firstly, Happy New Year to you all!

I could really do with some more input on this please?

Would also appreciate it if someone knows roughly how many kwh on average economy 7 water heaters/boilers use.

Thanks

It depends on how much hot water you use and how well your cylinder is insulated and what your incoming water temperature is and how hot you want the water to be. All immersion heaters are 100% efficient so it takes 0.0011kWh to heat 1 litre of water by 1 degree. The average temperature (over the year) of cold water is about 10 degrees. You would want the water to be about 60 degrees. So how much water do you use let's say 50 litres of hot water each person multiplied by 50 degrees multiplied by 0.0011kWh is 2.75kWh per person per day (assuming zero losses from the cylinder which could add another 2 or 3kWh per day).

Same calculation works with a kettle. 1 litre of cold water at 10 degrees heated to 100 degrees at 0.0011kWh per litre/degree. Multiply it all together and you get 0.099kWh rounded to 0.1kWh. A kettle may be rated at 2kW so should take 3 minutes to heat 1 litre of water.