How long to put the Immersion heater on for?

minibbb

I live in an all electric one bedroom flat with economy 7 and currently set the immersion to come on for an hour overnight to provide hot water for washing up/running the bath. I set it to come on at night to take advantage of the lower electricity costs.

Im not sure whether im not leaving it on long enough or not as i literally only have enough hot water to run one bath.

Should a normal size hot water tank provide more than this or is it likely that im just not giving the tank enough time to heat up? How long should i leave the immersion on for each day?

Many thanks!

david29dpo

You will have cheap rate between about 1200am and 7am so set the timer for 1.00am to 6.30am. The thermostat will cut out after about 2 hours depending on the setting. What is the stat set too?

HappyMJ

I don't think an hour is enough as david says 2 hours should be about right. It will reheat in less than that in summer but on a very cold winters night it will be fine. You could set it for 4:30 to 6:30 to save a penny or two.

Niowrtt

As the posts above, it is usual to run the tank during the whole off-peak period. The thermostat means that after heating up fully further energy is only used to top up the heat, which is actually a cheap way to maintain a tank of hot water.

However, you've mentioned a special case:
When you run a bath, cold water rushes into the tank and will dilute and steal heat some of the remaining hot water. Your tank's control may have a 'boost' option and you should use this between running two baths, at the cost of running it during the more expensive hours.

macman

It's better to run the immersion for longer on E7 rather than use the boost facility. If it properly lagged, it will retain the heat for many hours. If it's not, get it done straight away.
Obviously if you have a very small tank that will only run one bath, you need to use the boost. Check to see if the tank is hot all the way down after you get up.
A peak rate boost will cost about 3 times as much as E7.

ormus

hot water cylinders are typically 50 - 100 litres.
so a bath taking say 50 litres can empty a small cylinder.
even with a large cylinder, filling a second bath will result in warm/cool water, as cold water enters to fill the space left by the hot water.
hence you would require further heating, after the first bathfull.

27col

If you have a cylinder with sprayed-on solid insulation there is no need to switch the immersion heater off. The tank will just get up the required temperature and sit there at that temperature. There will be very little heat loss. If you use a little of the water then it will top the heat up, and you will always have nice hot tank of water ready for use.

HappyMJ

27col wrote: »

If you have a cylinder with sprayed-on solid insulation there is no need to switch the immersion heater off. The tank will just get up the required temperature and sit there at that temperature. There will be very little heat loss. If you use a little of the water then it will top the heat up, and you will always have nice hot tank of water ready for use.

It takes a minimum of 100W per hour just to keep a tank warm. (Also, assuming small tank and low 60 C temperature). At peak E7 rates that could cost quite a lot. It's cheaper to only heat it in the E7 period and as late as possible so that the tank is hot for the morning.