Can a shower be added to my consumer unit?

[JohnW2]

I'll base my calculations on my shower habits:
2 minutes/60 x 16.822p x 7KW [my Triton shower on low power] = 235.508/60p = 3.923p
2.5 minutes/60 [to allow for the time taken for the combi to strike from cold and the water to get to the shower, see quote below] x 2.941p x 27KW = 198.5175/60 = 3.31p

As I have mentioned to you in a PM (to which you elude below), those figures stretch the laws of physics ...

To revert to energy, rather than cost (i.e. kWh, rather than pence), you are suggesting that heating the same amount of cold water to the same temperature (at the shower head) uses 0.233 kWh of energy with your electric shower and 1.125 kWh with your combi.

That is surely a ridiculous suggestion? The amount of energy required to heat the same amount of cold water to the same temperature (at the shower head) will be identical in both cases. The only difference is that, in the case of the combi, slightly more energy will be required because of heat lost from the pipework and 'up the flue' etc.). However, that will be a relatively tiny about of energy, most certainly not enough to explain why the combi was using nearly 5 times more energy than the shower heater!! Where exactly do you suggest that the 'missing' 0.892 kW of 'lost energy' (nearly 4 times more than the shower used to heat the water!) went?!

The answer, of course, is that, as the energy consumption of your shower shows us, the combi cannot possibly have been running at 27 kW continuously for 2.5 minutes - in reality, only a small fraction of that (because of 'modulation'). Although you go on to say ...

Elsewhere the discussion about modulation has cropped up, it is my belief that little, if any, modulation will occur during a 2.5 minute shower.

As above, unless you are going to re-write the laws of physics, there must be a lot of 'modulation' involved.

Kind Regards, John

 

[Harry Bloomfield]

Well SUNRAY does.

As he won't believe it but my electricity from eon is 16.822p per kWh and gas is 2.941p per kWh. So yes I was wrong to say electricity was 4 times the cost of gas, it is actually 5.7 times the cost of gas.

Selective quoting!

 

[Harry Bloomfield]

As I have mentioned to you in a PM (to which you elude below), those figures stretch the laws of physics ...

To revert to energy, rather than cost (i.e. kWh, rather than pence), you are suggesting that heating the same amount of cold water to the same temperature (at the shower head) uses 0.233 kWh of energy with your electric shower and 1.125 kWh with your combi.

That is surely a ridiculous suggestion? The amount of energy required to heat the same amount of cold water to the same temperature (at the shower head) will be identical in both cases. The only difference is that, in the case of the combi, slightly more energy will be required because of heat lost from the pipework and 'up the flue' etc.). However, that will be a relatively tiny about of energy, most certainly not enough to explain why the combi was using nearly 5 times more energy than the shower heater!! Where exactly do you suggest that the 'missing' 0.892 kW of 'lost energy' (nearly 4 times more than the shower used to heat the water!) went?!

The answer, of course, is that, as the energy consumption of your shower shows us, the combi cannot possibly have been running at 27 kW continuously for 2.5 minutes - in reality, only a small fraction of that (because of 'modulation'). Although you go on to say ...
As above, unless you are going to re-write the laws of physics, there must be a lot of 'modulation' involved.

Kind Regards, John

John, you are over looking the fact that a combi has a much higher flow of water through it, than an electric shower does, therefore it needs an higher heat input. Try to run a combi at electric shower flow levels and it would constantly be cutting out.

The lesser flow of water through an electric shower is its main complaint and reason for many wanting a mixer shower. I find the flow from my electric shower is quite adequate for the purpose of taking a shower, in my comfortably warm bathroom.

 

[JohnW2]

John, you are over looking the fact that a combi has a much higher flow of water through it, than an electric shower does, therefore it needs an higher heat input. Try to run a combi at electric shower flow levels and it would constantly be cutting out.

You're comparing chalk with cheese.

If you have the (combi-heated) mixer shower 'turned on' to the extent that it delivers a lot more hot water than, yes, it will obviously use much more energy than a shower delivering less hot water.

However, if you 'turn down' the flow from the mixer so that it is the same as with the electric shower with which you are comparing, then the two will use roughly the same amount of energy, the only difference being that due to the small losses into the boiler/flue, and from pipework, in the case of the combi.

If one wanted to compare the fuel consumption of two cars, one with a top speed of 80 mph and the other with a top speed of 120 mph, one would not compare the consumptions of both at their respective top speeds - one would 'throttle back' the faster car to a speed no greater than 80 mph and would compare the consumptions of the vehicles when travelling at the same speed.

I find the flow from my electric shower is quite adequate for the purpose of taking a shower..

So do I, on the very rare occasions I use one of my electric showers. Hence, when (as I nearly always do) I take a shower using one of the mixer showers, I turn down the flow to something similar to that which the electric shower can provide.

Of course, some (maybe many/most) people may always leave a mixer shower 'turned on full'. In that case, the cost of the energy they use may well not be a lot less than the cost of an electric shower - but that is because they have chosen to heat a lot more water, not because of issues relating to fuel costs, 'delay times' etc!

They could obtain the same high flow by using a hypothetical 25 kW electric shower - in which case the dramatic difference in cost (if one compared 'chalk with chalk') would become apparent

Kind Regards, John

 

[SUNRAY]

You're comparing chalk with cheese.

If you have the (combi-heated) mixer shower 'turned on' to the extent that it delivers a lot more hot water than, yes, it will obviously use much more energy than a shower delivering less hot water.

However, if you 'turn down' the flow from the mixer so that it is the same as with the electric shower with which you are comparing, then the two will use roughly the same amount of energy, the only difference being that due to the small losses into the boiler/flue, and from pipework, in the case of the combi.

If one wanted to compare the fuel consumption of two cars, one with a top speed of 80 mph and the other with a top speed of 120 mph, one would not compare the consumptions of both at their respective top speeds - one would 'throttle back' the faster car to a speed no greater than 80 mph and would compare the consumptions of the vehicles when travelling at the same speed.

So do I, on the very rare occasions I use one of my electric showers. Hence, when (as I nearly always do) I take a shower using one of the mixer showers, I turn down the flow to something similar to that which the electric shower can provide.

Of course, some (maybe many/most) people may always leave a mixer shower 'turned on full'. In that case, the cost of the energy they use may well not be a lot less than the cost of an electric shower - but that is because they have chosen to heat a lot more water, not because of issues relating to fuel costs, 'delay times' etc!

They could obtain the same high flow by using a hypothetical 25 kW electric shower - in which case the dramatic difference in cost (if one compared 'chalk with chalk') would become apparent

Kind Regards, John

One of my properties is due to be empty in a little while, it has a prepay meter which I think has the ability to display all sorts of readings [the electric pp meter certainly does], we usually have to do a decent clean and touch up, repair taps etc and could be a perfect opportuntiy to do some tests.

 

[Harry Bloomfield]

Of course, some (maybe many/most) people may always leave a mixer shower 'turned on full'. In that case, the cost of the energy they use may well not be a lot less than the cost of an electric shower - but that is because they have chosen to heat a lot more water, not because of issues relating to fuel costs, 'delay times' etc!

Which is the way most typical users seem to use them, they scoff at what they suggest is the poor output of an electric shower, perhaps you are an exception? The move generally seems to be towards higher and higher flow rates from showers generally.

 

[JohnW2]

Which is the way most typical users seem to use them, they scoff at what they suggest is the poor output of an electric shower, perhaps you are an exception?

Maybe - but you said that you were another such 'exception', didn't you?

The move generally seems to be towards higher and higher flow rates from showers generally.

It does.

However, in terms of how this discussion arose, if people decide that they want a shower which delivers hot water at 3-4 times the flow rate that an electric shower produces, they are thereby 'volunteering' to use 3-4 times more energy for a shower, which (as SUNRAY suggested) more-or-less cancels out the dramatic difference in prices of the two fuels.

As I said, if the choice they had (which it obviously isn't) to get them different flow rates was between a 7 - 10 kW electric shower and a 27 - 35 kW electric shower, then they would become rapidly aware of the cost of their desire for a higher flow rate!

Kind Regards, John

 

[JohnW2]

One of my properties is due to be empty in a little while, it has a prepay meter which I think has the ability to display all sorts of readings [the electric pp meter certainly does], we usually have to do a decent clean and touch up, repair taps etc and could be a perfect opportuntiy to do some tests.

Fair enough.

However, as I've just been discussing with Harry, if you plan to make any comparisons, make sure that you compare chalk with chalk (or cheese with cheese). As I've just written, if people decide that (with a combi-powered one) they want 3-4 times more hot water delivered during their shower than would be possible with an electric show, they need to understand and accept that it is going to use roughly 3-4 times more energy - thereby, as you have suggested, making the cost of a (high flow rate) combi shower not a lot less than the cost of a (lower flow rate)n electric one.

Kind Regards, John

 

[SUNRAY]

Which is the way most typical users seem to use them, they scoff at what they suggest is the poor output of an electric shower, perhaps you are an exception? The move generally seems to be towards higher and higher flow rates from showers generally.

My Triton 10.5KW has 3 elements, High power uses 3 and Low power uses 2 so I guess they are 3.5KW each. It has to be really cold incoming cold water before I switch it to high and even then the the flow and hence pressure required to limit the temp I find uncomfortable against my skin. I will add that we keep the head descaled which is a common failing for many people and I automatically take a jar and bottle of descaler for calls to poor shower performance.

 

[JohnW2]

My Triton 10.5KW has 3 elements, High power uses 3 and Low power uses 2 so I guess they are 3.5KW each. It has to be really cold incoming cold water before I switch it to high and even then the the flow and hence pressure required to limit the temp I find uncomfortable against my skin. I will add that we keep the head descaled which is a common failing for many people and I automatically take a jar and bottle of descaler for calls to poor shower performance.

Does that not reinforce my point that if you used a (combi-powered) mixer shower and turned down it's flow rate to something similar to the electric one, you would get a similar shower at very much lower cost?

Kind Regards, John

 

[JohnD]

making the cost of a (high flow rate) combi shower not a lot less than the cost of a (lower flow rate)n electric one.

'mmmmm, a much better shower at a slightly lower cost....

Bargain!

 

[SUNRAY]

Does that not reinforce my point that if you used a (combi-powered) mixer shower and turned down it's flow rate to something similar to the electric one, you would get a similar shower at very much lower cost?

Kind Regards, John

Having never knowingly had a shower from a modern combi I'm not in a position to make a comment but there has to be a limit to the temp and water flow against the skin, the thought of 4 times the water through the boiler and another 4 times of cold to counteract the temp is way outside my comprehension, regardless of design of showerhead.

 

[JohnW2]

'mmmmm, a much better shower at a slightly lower cost.... Bargain!

Some may, indeed, think that way.

That's fine, so long as they realise that it could be reduced to around a quarter of the cost if they could be satisfied with a 'not so good shower' such as would be supplied (to millions of people) by an electric shower.

People vary a lot, in ways which are not necessarily all that understandable/logical/rational. My late FIL had a perfectly good combi-powered mixer shower into the bungalow into which he retired. When he stayed with us here, he found himself using a 7.5 kW electric shower is a little-used dusty corner of oiur house. He was so 'impressed' that, despite my attempts to dissuade him, he had his mixer shower ripped out and replaced by a fairly low-power electric one. 'Horses for courses', I suppose!

Kind Regards, John

 

[JohnW2]

Having never knowingly had a shower from a modern combi I'm not in a position to make a comment but there has to be a limit to the temp and water flow against the skin ...

I have a little experience, in that one of my daughters has such a setup. As with any mixer shower, the temperature can be adjusted all the way from 'all cold' to as high as the built-in temperature-limiting (and incoming hot water temp) allows - and flow rate control is separate from that. I'm not sure what sort of 'limits' you're talking about.

Kind Regards, John

 

[SUNRAY]

I have a little experience, in that one of my daughters has such a setup. As with any mixer shower, the temperature can be adjusted all the way from 'all cold' to as high as the built-in temperature-limiting (and incoming hot water temp) allows - and flow rate control is separate from that. I'm not sure what sort of 'limits' you're talking about.

Kind Regards, John

I'm talking about temp' safety limits to prevent scalding and flow rates to prevent being pushed over [tongue in cheek]