Shower or bath?

[Black Hole]

Yep, but you would need to pump the water up to it.

 

[Trev]

And you would need a pretty high water tower to store it in. 3 bar (typical) would require about 110ft head

 

[Wallace]

And you cant have too much head....[Cough]

 

[MikeSh]

So what? It works, even when filling the bath.

When we had the combi it took 20 minutes to run a bath. It was utterly mad.
Now, with the mains pressure system it takes 6 minutes .... provided the hot tank is hot

 

[gomezz]

The third option is a strip wash in the basin. Good for a quick unstickifying before doing something physical but probably not sufficient if going on a hot date.

 

[Deleted member 473]

The third option is a strip wash in the basin. Good for a quick unstickifying before doing something physical but probably not sufficient if going on a hot date.

Too much detail.

 

[Deleted member 473]

And you would need a pretty high water tower to store it in. 3 bar (typical) would require about 110ft head

But we only need to match BH's stopcock throttled pressure of 0.1 bar!

If you almost close the stopcock, that is hardly mains pressure, is it? It could be anything from, well, 0 to mains pressure?

Anyone know what the volume of a typical bath is? 100l? 300l?

 

[magic.m]

Given the choice I'd have a bath every time, although time usually dictates otherwise.
I'd say for our household that a shower is good for a quick rinse but for a propper wash there's not going to be much cost saving to be had (long showers).

Did an evening course a few years ago with sombody who changed the circuit breaker for the shower for a smaller rating that happened to trip after about 8 mins from cold with his shower. He thought it was a great idea to speed up his son. I never did find out what happened the first time his wife went in straight after his son...

When we had the combi it took 20 minutes to run a bath. It was utterly mad.
Now, with the mains pressure system it takes 6 minutes .... provided the hot tank is hot

Does sound like your combi was either defective or completely inadequate.

Several of the family had early models installed that were nothing but trouble but the ones on the market now seem to be mostly of a good standard. Our's (about 3yr old) will fill the bath just as quick as the old gravity system - about 5 mins - admitadly not as hot but still enough to wince at.

 

[MikeSh]

Does sound like your combi was either defective or completely inadequate.

It worked fine. It was a Vaillant as I wanted to avoid some of the c**p being sold at that time. (prob about 8 years ago.)
Inadequate, yes. The problem was twofold, I sized the boiler for the central heating load AND we have a large bath which is well filled. With hindsight I should have got a larger boiler, but that obviously had both capital and long term economy implications at the time. In fact that would only have given about 30% more output anyway, so it would still have taken a good while to fill the bath (and more to the point SWMBO would still have complained about the trickle shower).

 

[talos]

Had a combis both oil and mains gas for the last 20 years, with a thermostatic shower mixer and always had a good shower. We did an experiment when we left the plug in the bath and measured the depth of water after showering for 10 mins, the resulting depth was 7 inches, insufficient in my opinion for a decent bath. I think there is some confusion between mains pressure and flow rate, both of our combis have produced hot water at mains pressure this is essential for thermostatic mixers to work efficiently, the thermostat regulates the flow of the hot water to reach and regulate to the required temperature. The old electric shower we once used was totally useless and incredibly expensive to run, the flow rate was so low you could hardly get wet.

 

[Deleted member 473]

I reckon an average bath must contain at least 1/3 cubic metre or water, which would cost about £1.15.

How much 330l costs to heat to whatever is a reasonable temperature from whatever temperature it was at when it entered the house is a task I will try later. (Unless someone else wants to have a go.) Let's assume gas at about 4p/kWh and electricity at 12p/kWh.

 

[Trev]

To heat 330l water through 35 degrees C requires about 330 x 1000 x 35 = 11.5million calories.
1.16222222 × 10-6 kilowatt hours = about 10kWh
Assume a electric conversion rate efficiency of 80% and gas of 60%
Electric 10kWh @ 12p /0.8 = £1.50
Gas 10kWh @ 4p /0.6 = £0.66

Does this pass the 'sanity test'? I think so.

PS. Where do you buy your electric?

 

[talos]

You also have to factor in that a drawn bath is constantly cooling, whereas a shower temp should be constant. Also a bath when drawn can be sat in until cold at no extra cost. To run a shower for the same length of time would incur an on-going cost.

 

[Trev]

You also have to factor in that a drawn bath is constantly cooling,

Putting the 'lost' heat into the bathroom.

whereas a shower temp should be constant.

Putting the 'lost' heat down the plughole

 

[Deleted member 473]

Putting the 'lost' heat into the bathroom. Putting the 'lost' heat down the plughole

And a lot of damp, too, which an extractor fan will suck outside, together with heat from the house. Oh dear!

Thanks for the calculation! I had to go out and it was waiting for me when I got back, so that was a pleasant surprise!

I was slightly disingenuous as the efficiency of a gas boiler is not 100%...still, even with gas heated baths it looks like the 30 minute shower is ahead of the bath in total price. The 1 minute shower at 5p is well ahead.

Electricity and gas? EDF Energy dual fuel fixed price until 2015. Why? Am I paying too much?

 

[Trev]

No. I was thinking the opposite.

 

[Deleted member 473]

So, frightening thought!

For one person taking an electric shower for 1 minute every day of the year, total cost: £18.25. (£18.30 on a leap year!)
For one person taking an electric shower for 30 minutes every day of the year, total cost: £547.50.
For one person taking a bath every day of the year, heated by gas, total cost: £660.65.
For one person taking a bath every day of the year, heated by electricity, total cost: £967.25.

Now multiply those by 2 or 4 and those costs are even more frightening...
Thanks to Trev for the fuel calculations. Any other errors are mine.

 

[Deleted member 473]

No. I was thinking the opposite.

I went back to my bill. There is a standing charge of 18p per day, which brings the cost I pay to about 13p, but I am not sure how I should handle that, as the marginal cost seemed more appropriate to the calculations. However, yes, with my consumption levels, I pay 13p per kWh. It all depends on how much electricity you use in total. The marginal cost is 11.96p.

Similarly, the standing charge on gas is 25p per day, but that brings the cost per kWh up from 3.785p to 4.04p.

 

[Trev]

Not sure whether my gas/electric efficiency figures are anywhere near correct. I just Googled and plucked them off a couple of pages that seemed to pretty much agree.

 

[Deleted member 473]

Not sure whether my gas/electric efficiency figures are anywhere near correct. I just Googled and plucked them off a couple of pages that seemed to pretty much agree.

I found the manual for my gas boiler. The efficiency is 88.4%. It is about 3 years old now.

I had always assumed electricity was 100% efficient, just more expensive.

Edit: Found this for gas boilers:

http://www.boilers.org.uk/