When is increased electric shower power not worth it?

aardvark7

I currently have a 10.5kw shower and it is playing up (only one of the two heaters working I think), so I'm looking to replace it. The obvious choice is another 10.5kw unit, but I'm wondering about the wisdom of it and can find no help whatsoever.

Basically, my stepson has an 8.5kw unit and there seems little or no difference to the flow/power. So what I am wondering is whether there is a limit to any advantage of having a powerful electric shower if the water pressure is insufficient. In other words, could it be that an 8.5kw shower has more than enough power to heat all the water coming through our pipes, so that a 10.5kw shower would only actually be using 8.5kw even when on full?

Without having flow rate or pressure testers I can't know the strength of our water supply, and shower manufacturers don't seem to say anywhere that if your water pressure is limited then there is no point getting a high power unit! The only advice one can read is that the more powerful the shower rating, the stronger the shower.

Does this remain true in all cases, or only those houses lucky enough to have a powerful mains pressure?

Jonesya

I think in most electric showers the power output normally has a couple of fixed settings and then the temperature is controlled by varying the flow of water past the heating element.

If you're using the 10.5kw shower on full power setting then its taking the full 10.5kw to heat whatever flow you get from it. If you drop to 8.5kw, then for the same temperature at the outlet you'll get less flow - about 20% less.

If you're running the shower on the low power setting and don't use it at full power then you might want to look at a lower powered shower, or if you would prefer less flow/ power consumption.

macman

If the circuit is already cabled for 10.5kW, then to keep the same flow you need to replace like with like. You can't really compare to another install, as there are too many variables.

aardvark7

Thanks for the answers, although they don't really resolve my question, so I'll try to rephrase it.

Basically, there is a maximum water flow. Every house, after all, has to make do with what the water company supplies.

If, with only that pressure available, a shower produces a maximum stream of water that can be heated to the desired temperature by 8.5kw, what use is the extra 2kw? Would that only come into play if the person getting showered wanted to be scalded?

If this is a possible scenario, how do you know what is the maximum usable power for a given flow?

Just as an example, looking at some Mira showers, they state working pressures, but say nothing of flow rates. So it may well be that the more powerful shower would allow through more water if it was at the top of that pressure range, but for a weaker flow it will use less power and, effectively, become an 8.5kw unit.

Part of the reason I am asking this is because the behaviour of our existing shower has changed. Although the flow seems about the same, the temperature dial has to be almost to maximum. Even in cold winters before it was only ever just above halfway. This makes me think only one of two elements is functioning and that just the one is providing a similar performance. Only the dial is in a different position.

Just in case you wonder, we have very soft water and there are no blockages or leaks!

Ectophile

If the shower is too powerful for the flow of water, then you may struggle to keep it to a safe temperature on the highest power setting.

As Jonesya says, the more basic showers just have a couple of heat settings (plus cold), and a big dial which actually controls the water flow. If the mains water flow is too low, then a full 10.5kW could deliver scalding hot water, even with the flow turned up to maximum. At that point, you'd have to just set it to the lower power setting.

It's worth bearing in mind that the right power in winter may be too high in summer. I run my 8.5kW shower on the "Eco" (middle) power in summer, but by late autumn, the incoming mains water gets so cold that I have to turn it up to "High".

I might also add that a massively powerful shower running at full power would be using an awful lot of electricity and water. So it's not particularly money saving, or eco-friendly, compared with having a bath.

zaax

The higher the kw the more more hot water you get. The colder the water (like now) the more power is needed to get it hot. If you can go for a 12kw

Ectophile

Twelve kilowatts! That's 50A at 240V. My whole house only has a 60A supply.

I've just got an 8.5kW shower, and it works fine for me.

[Deleted User]

aardvark7 wrote: »

Basically, there is a maximum water flow. Every house, after all, has to make do with what the water company supplies.

If, with only that pressure available, a shower produces a maximum stream of water that can be heated to the desired temperature by 8.5kw, what use is the extra 2kw? Would that only come into play if the person getting showered wanted to be scalded?

So you're telling us that you can't get a flow rate that's fast enough to prevent your 10.5kW shower from scalding you? If that's the case there's something wrong with your plumbing.

(Measuring flow rate is easy, all you need is a bucket and a watch. For that matter measuring the power output of your shower is also easy, all you need is a bucket, a watch and a thermometer.)

richy999

The extra 2kw over the 8.5KW will mean that at full temperature, you will get greater flow out of the shower, but will use more electricity. The 8.5KW shower will have to reduce the flow of water through it in order to maintain the temperature, but will use less electricity.