Heating costs

[Xdavid]

Does anyone know a simple formula to judge whether it's cheaper to run the hot water from an immersion heater or from an oil-fired CH boiler? I guess it's cost-effective to use the boiler in winter when the CH is on too, but what about in summer?

 

[PlumbingExpert]

You need to compare the electricity consumption per x minutes, and multiply that by the time ti takes to reach the required temperature.