What ever cost you save in water you will lose in the extra costs of heating the water with electricity
This is what I thought also.
Depends on the output you want too - 6L of water will be used up in no time and then that's it really if it only has a 1.5Kw element.
No way of shortening the run to the utility?
This is the real life thing. Very well put. How much hot water is used each time, will change as to if electric or gas/oil works out best. Also summer and winter. If there is half a bowl full of water cooling in the pipes after using hot water, in winter it is not wasted, it is heating the home, in summer it may cost more as an air conditioner is cooling the home so has to work harder.
So to fill a twin tub on washing day, we use a lot of hot water, same with filling a bath, so oil/gas is far cheaper. But to wash one's hands, is a very different story, where maybe up to 10 times the water required is heated.
As to a gas boiler, it also heats the heat exchanger, so even before the water leaves the boiler warm, there are losses.
@Madrab may be able to tell us the losses with a combi boiler, I have an oil boiler, 20 kW and found to get DHW it runs around 20 minutes a day, so per 28 days, around 186 kWh, the immersion heater uses around 35 kWh, so on balance the immersion is cheaper to run, even when oil is cheaper than electric.
However, at standard rate electric, the difference in cost is small. And I could reduce costs by having local water heating, but the cost of installing those heaters is not really justified.
There is also the energy storage, if I use off-peak, or PV solar to heat my DHW when excess available it is cheaper than using electric as and when DHW is required. I have 6.4 kWh of stored electric, if it runs out, then my energy cost goes up. Setting up 5 electric water heaters with timers to use off-peak would cost a fortune, so simply not worth doing.
A unit like this
would save me money, but would take up valuable space under the sink, and would take years before it paid for its self. And a unit like this,
smaller, but cost of cable to consumer unit means costs even more to fit, and at 3.5 kW it would likely result in using more peak power.
The reduction in oil use, when I swapped from oil to electric for DHW was far higher than I expected. Will only use oil to heat DHW after having a bath. Since no longer use a twin tub, my washing machine, dishwasher and drier all use electric and yes it does save using between 00:30 and 05:30 but not enough to worry about.
