Turn off water heater 3 days a week?

ms3ssippi

Hi,
In the flat we have an unvented water heater. In the first months I've seen our Night Rates Kwh are 2x higher than the Day Rates. I found out the water heater off peak turns on twice within the Night Rate (4AM-5AM and 6AM-7AM). So I made the adjustment and just schedule it from 5AM-6AM, and this lower the Night Rate significantly but still higher than the Day Rate. Next, I experimented by turning off the controller 3 days a week since we don't use all the heated water and that we don't need the off peak turning on  everyday. My rule of thumb is if the pipe coming out from the tank is still hot by touch I keep it off. This has also lowered the Night Rate below the Day Rate in the last 2 months.

My questions are, would I break of damage the water heater when I turn it off like this? And is this experiment correct that even if the heater is turned off the water that has already been heated remains hot for some time?

Thanks!

[Deleted User]

I am confused. What type of tariff are you on? If it is an E7 tariff,then 7 hours are usually at the cheap rate overnight.

What does your statement say? It is possible that the supplier has transposed your meter index readings as far as your bills are concerned.

Section62

Dolor said:

I am confused. What type of tariff are you on? If it is an E7 tariff,then 7 hours are usually at the cheap rate overnight.

I suspect the OP means their night consumption is twice their day consumption, which obviously isn't unexpected where overnight electric heating is in use.

Not that the night unit cost is twice as expensive as the day unit cost.

Olly_J

I think the OP means his KWh used at night is twice the amount used in the day, due to the water heater coming on twice during the off peak period every day.

There should be nothing wrong with heating your water less often in an unvented cylinder, long as its hot enough for your usage its fine, as its direct from the pipe to the tank.

Section62

ms3ssippi said:

My questions are, would I break of damage the water heater when I turn it off like this? And is this experiment correct that even if the heater is turned off the water that has already been heated remains hot for some time?

You shouldn't damage the heater element by having it switched off, and yes, if the system you have stores a volume of hot water and is well insulated, the water will stay hot for an amount of time, depending on the amount of hot water you use.

ms3ssippi

Thanks for all your answers! Am new to the UK and coming from a tropic country these heaters are new to me. I forgot to mention that when our Night Rate Kwh is 2x more than our Day Rate only the fridge and the water heater are the ones running within the cheaper Night Rate, which made it easier to narrow it down to the off-peak water heater controller.  

[Deleted User]

The $64K questions are how much hot water is the OP using in a day, and how well lagged is the cylinder? I have a 250l unvented HW cylinder. This morning I had a shower and my wife had a bath plus the usual washing of a few cups and plates. My HW cylinder is showing maximum temperature reached (60C) and, so far, total usage for water re-heating is 1.97kWh. 

FreeBear

Section62 said:

ms3ssippi said:

My questions are, would I break of damage the water heater when I turn it off like this? And is this experiment correct that even if the heater is turned off the water that has already been heated remains hot for some time?

You shouldn't damage the heater element by having it switched off, and yes, if the system you have stores a volume of hot water and is well insulated, the water will stay hot for an amount of time, depending on the amount of hot water you use.

Look up the specifications for the cylinder - There should be a line giving a heat loss figure in terms of KWh/24h - This will give you an indication on how long the immersion heater needs to run to maintain the water at temperature assuming no hot water has been used. 2KWh per day is fairly typical. You can reduce this a little by turning the thermostat down to 50-60°C. Being a sealed system, there won't be a header tank, so you could even reduce the temperature down to 45°C as there will be an almost zero risk of Legionella.

Turning the timer off altogether is also an option (as long as the clock has a backup battery). No point in heating a full tank every day if you only use a few litres for washing up (boil a kettle) and bath once a week. That said, if you shower daily, and the hot water comes from the tank, cold showers are not always welcome.

EssexHebridean

There is still the point to be made here that with a correctly set up E7 system you not only expect, but actively want the use overnight to be higher than during the day! On average over a year ours is currently about 25% day/75% night - sadly I'm not convinced I can get the night use improved much on that now! 

We're also playing about with leaving the immersion off at the moment - my gut feeling is that we'll heat it fully once a week - probably on a Saturday night, then do a short top-up on a Monday morning before the night rate clicks off, and then it'll stay off through the week at the moment. 

wittynamegoeshere

Our hot water cylinder has been switched off since we moved in to our electric-only house.  We have an electric heated shower and a dishwasher, so no need for hot water for the essentials.  If I want a bucket of hot water, e.g. to wash the car, I just use the kettle, it really isn't a big deal.  Washing hands in cold water seems to be adequate, if not then the second bathroom I've refitted has an instant hot water system supplying the basin.

Keeping a water cylinder permanently hot is expensive, especially if using standard rate electric, however modern and well insulated it is.

Depending on its location, it will make the building warmer, which may mean the heat is useful rather than wasted in winter but this same heat is extremely unwelcome in the summer, especially if near the bedrooms as they often are.

EssexHebridean

Yes - I can possibly see us rethinking how often ours goes on in the winter because the of the small amount of heat leakage, plus the fact that once the clocks change, the night rate is less user-friendly to doing things very first thing. 

Electric shower and dishwasher here too, but by the time face washing and MrEH's shaving are take into account some hot water for at least part of the week without having to mess about boiling kettles is welcome to reduce the amount of faffing required! Add in the fact that we have knives and pans that there is no way I'm putting anywhere near the DW, and it becomes less cut & dried for us.