Immersion heaters

[mikeclaude]

Someone told me it would be more energy efficient to leave a thermostatically controlled immersion heater on all the time to heat a boiler, rather than heat it up from cold once a day. I'm not sure if that makes sense?

How many degrees per hour would you expect hot water in a foam insulated 55 litre boiler to lose? If it was 2 degrees/hour for example, that would mean an immersion would need to heat the water a total of 48 degrees if left on all day.

On the other hand if the immersion is switched on once a day to heat cold water from 10 degrees to 60 degrees it works out to 50 degrees - about the same.

[Chris]

Heat loss is proportional to the temp of the water in the tank, so if you only heat it for when you need it, that's cheapest. Except that if you heat it at night it will cost you less if you have Economy 7.
Any pipe near the tank which feels hot, is worth insulating. If the tank's old, its insulation won't be very good, so extra old sleeping bags/blankets will save you money too.

[mikeclaude]

Thanks