Water heater elec usage dependent on water usage?

nohassles

Apologies if I don't use the right terminology, and also if this is a stupid question... I'm still getting to grips with "adulting".

Although I'm not on an economy 7 tariff, my boiler works on heating the water overnight and storing it. My question is: if I use very little hot water in a day, does it require less energy to replenish the hot water overnight, compared to if I completely empty the tank?

In the process of writing this, it seems like it should be the case - I imagine there must be some loss of heat during the day, but I would still expect that a lot of it is preserved and therefore it takes less to reheat than starting from scratch?

coffeehound

Yes you are right. Assuming that your water cylinder is fairly new, it won’t lose much heat over the course of 24 hours so your boiler just needs to top up the temperature. Modern cylinders lose less than 2 kWh per 24 hours. For your gas usage that is pennies per day.

wavelets

nohassles wrote: »

Apologies if I don't use the right terminology, and also if this is a stupid question... I'm still getting to grips with "adulting".

Although I'm not on an economy 7 tariff, my boiler works on heating the water overnight and storing it. My question is: if I use very little hot water in a day, does it require less energy to replenish the hot water overnight, compared to if I completely empty the tank?

In the process of writing this, it seems like it should be the case - I imagine there must be some loss of heat during the day, but I would still expect that a lot of it is preserved and therefore it takes less to reheat than starting from scratch?

Try this experiment.

Fill an electric kettle with cold water and time how long the kettle takes to boil that water.

Once boiled, reboil the same water whilst still hot, and time that.

A kettle is just a type of small boiler.

You can consider time equivilent to the energy input - as a kettle consumes a constant amount of energy over time - energy that is then transferred to the water to raise it's temperature.