Electric boiler?

[plugwash]

All true, but, if we are "massively exposed to gas prices", and a net importer of it, why is it that gas is so much cheaper than electricity in the UK?

Fundamentally one would expect electricty generated from gas to be more expensive per kWh than gas itself, because gas power plants are only about 55%-60% efficient and because of capital and maintinance costs but that alone doesn't really explain the massive difference seen in the UK.

Still I suspect a large part of the reason for "why is the difference so large" is related to renewables, which both receive direct subsidies but also make the demand for traditional electricity generation far more volatile.

 

[JohnW2]

Fundamentally one would expect electricty generated from gas to be more expensive per kWh than gas itself, because gas power plants are only about 55%-60% efficient and because of capital and maintinance costs ..

Yes, I understand all that, but as you go on to write ...

... but that alone doesn't really explain the massive difference seen in the UK.

Still I suspect a large part of the reason for "why is the difference so large" is related to renewables, which both receive direct subsidies but also make the demand for traditional electricity generation far more volatile.

Yes, that would all make sense - at least, it would were it not for the fact that (I believe, but may be wrong) a large price difference existed long before we'd even heard of 'renewables', didn't it?

 

[ericmark]

Fundamentally one would expect electricty generated from gas to be more expensive per kWh than gas itself, because gas power plants are only about 55%-60% efficient and because of capital and maintinance costs but that alone doesn't really explain the massive difference seen in the UK.

It is not the efficiency, it is the start-up and run down times. Connah's Quay combined power gas/steam turbines take around 48 hours to get to maximum and to stop again. Moving for 50% to 75% output quite quick, but 25% to 95% that's slow, as the gas turns the turbine, then the waste heat makes the steam, which then feeds to steam turbine bit. So running around 80% efficiency at a constant output of 50% and as the output increases the efficiency improves.

This is why we need the electric mountain. When it can go from zero to full output in around 1 minute.

I suppose having a generator at home powered by gas or oil, which can drive a heat pump would be the cheap way, but the government now charges road tax on generators, to stop us doing that.

 

[Harry Bloomfield]

You're presumably talking about baths again - and, as I recently wrote, everything would get much simpler and more sensible if the practice of taking baths were to largely disappear. I suspect it's already pretty uncommon - the majority of people I know about ('friends and family' etc.) seem to already be 'showers-only' people.

You cannot beat, a long relaxing soak in a hot bath.

Living alone, one of my early flats, lacked both a bath, and a shower. It was rented to me, cheap, and planned for a full refurb. As a work-around, I bought a portable shower - curtain hanging from a square metal bracket, plastic fold up tub base, and the clever bit - a pump-up air pressurised sprayer, similar to the garden weed-sprayers. You simply filled it with warm water, pressurised it, and got on with it. Then at the end, you had to empty the tub away.

My next flat, had a bath, with the hot water heated by one of those instant gas boilers, like a combi, but it didn't serve the heating, it had E7 for that. That took for ever to fill the bath, but had a fit over the taps shower adaptor. It was near impossible to get the shower temperature balanced, so often as not, I would simply fill the bath.

An elderly friend, had a bath, plus cylinder heated by a gas boiler. He was persuaded to do away with the cylinder, and swap the system to a combi, and revise the bathroom, by doing away with the bath, fitting an electric shower. He came to regret his choice, due to the long delays waiting for the hot water to appear, and having no chance to soak in a hot bath.

Now, I have a bath, filled via a cylinder, heated by a gas boiler, with an high power thermostatic electric shower over the bath. We tend to bathe on alternate days, and shower the others. If you turn the bath taps on, before you start getting undressed, the bath is full, ready when you are ready to get in.

 

[Harry Bloomfield]

but the government now charges road tax on generators, to stop us doing that.

Did you mean road tax rates on the fuel needed for generators?

 

[ericmark]

Did you mean road tax rates on the fuel needed for generators?

Yes, now need to use DERV or diesel engined road vehicle fuel for generators.

 

[JohnW2]

It is not the efficiency, it is the start-up and run down times.

The 'efficiency' which matters in the context we're discussing refers to the amount of electricity generated by a certain amount of gas, and that remains the case regardless of the 'mechanism' which, in practice, results in a 'loss of energy' in the conversion.

 

[JohnW2]

You cannot beat, a long relaxing soak in a hot bath.

I realise that some people have that view but, as I thought we had agreed, it really needs to be thought of as a 'luxury'.

Enjoying that luxury not only invokes increased running costs (heating more water) but also appreciably increases the complexity, cost and 'space requirements' of the plumbing installation. People who want to enjoy this luxury should therefore be aware of those 'downsides' and be happy to accept them.

As I've said before, the concept of storing hot water is not a very good one since, no matter what measures one takes (at a cost), there will always be some heat losses - which represent a 'waste' of energy (hence cost) during some parts of the year.

An elderly friend, had a bath, plus cylinder heated by a gas boiler. He was persuaded to do away with the cylinder, and swap the system to a combi, and revise the bathroom, by doing away with the bath, fitting an electric shower. He came to regret his choice, due to the long delays waiting for the hot water to appear, and having no chance to soak in a hot bath.

I'm not sure that I understand "long delays waiting for the hot water to appear", particularly for an electric shower, but also for taps in general - where the delay will be a function of the distance of taps from the ;'source', be that a combi or a storage cylinder.

A friend of mine has implemented a sort-of 'compromise' (to facilitate occasional baths), but I don't think I've heard of anyone else doing it. He has a combi boiler, which supplies his radiators and most taps (and I think probably also a shower). However, he also has a (vented) DHW cylinder (and header tank) and can 'switch things' such that the combi heats water in the cylinder - which he uses for filling baths once or twice per week. I'mnot sure whether the bath is only supplied from the cylinder or whether he has some sort of 'clever change-over system', and nor am I sure whether his shower can be supplied from the cylinder.

 

[Harry Bloomfield]

Enjoying that luxury not only invokes increased running costs (heating more water) but also appreciably increases the complexity, cost and 'space requirements' of the plumbing installation. People who want to enjoy this luxury should therefore be aware of those 'downsides' and be happy to accept them.

I went to the trouble of costing a gas stored hot water bath, versus a shower, one of my quick showers. Whilst one of my quick showers is cheaper, many people do spend much longer under an electric shower, and so could easily exceed the cost of a bath. At least a bath is limited in consumption.

I'm not sure that I understand "long delays waiting for the hot water to appear", particularly for an electric shower, but also for taps in general - where the delay will be a function of the distance of taps from the ;'source', be that a combi or a storage cylinder.

You obviously don't have a combi, or you would understand. You have delays whilst the gas flame heats the heat exchanger, then more delays, until the hot water gets to the tap. If you are running the water for a bath, the flow is much less than were it from a pre-heated cylinder.

 

[JohnW2]

I went to the trouble of costing a gas stored hot water bath, versus a shower, one of my quick showers. Whilst one of my quick showers is cheaper, many people do spend much longer under an electric shower, and so could easily exceed the cost of a bath. At least a bath is limited in consumption.

Fair enough.

You obviously don't have a combi, or you would understand.

I don't, but several of my family members do, so I'm well familiar with them.

You have delays whilst the gas flame heats the heat exchanger, then more delays, until the hot water gets to the tap.

'Horses for courses'! It obviously depends to some extent upon how hot the exchanger is when turns on the tap (or shower) (and if it is 'cold', there will certainly be some delay) but I think the main issue is that of the distance from 'source of hot water' (combi or cylinder) to the tap/shower. It is certainly the case that in the (relatively small/average size) homes of my family members with combis, hot water appears at taps/shower (from their combi) much quicker than it does (from cylinder) in my (very large) house, in which some of the taps/showers are considerable distances from the cylinder.

If you are running the water for a bath, the flow is much less than were it from a pre-heated cylinder.

I think we've all agreed that trying to fill a bath from a combi is a pretty crazy idea. As far as I am concerned 'combi means no baths'

 

[Harry Bloomfield]

It is certainly the case that in the (relatively small/average size) homes of my family members with combis, hot water appears at taps/shower (from their combi) much quicker than it does (from cylinder) in my (very large) house, in which some of the taps/showers are considerable distances from the cylinder.

Then I would suggest your expectations, are clouded by what you are accustomed to in your own home. The major complaint from combi owners, is the delay involved, before heated water appears out of the combi.

 

[JohnW2]

Then I would suggest your expectations, are clouded by what you are accustomed to in your own home. The major complaint from combi owners, is the delay involved, before heated water appears out of the combi.

None of my relatives have such complaints, but that is perhaps at least partially because, in all cases, the distance from their combi to taps/showers is very small. In the house I know best, the combi in the kitchen is about 1 metre from the kitchen tap, and the shower and bathroom basin taps are probably less than 2m away in the bathroom immediately above the kitchen.

 

[ericmark]

I'm not sure that I understand "long delays waiting for the hot water to appear", particularly for an electric shower, but also for taps in general - where the delay will be a function of the distance of taps from the ;'source', be that a combi or a storage cylinder.

A friend of mine has implemented a sort-of 'compromise' (to facilitate occasional baths), but I don't think I've heard of anyone else doing it. He has a combi boiler, which supplies his radiators and most taps (and I think probably also a shower). However, he also has a (vented) DHW cylinder (and header tank) and can 'switch things' such that the combi heats water in the cylinder - which he uses for filling baths once or twice per week. I'mnot sure whether the bath is only supplied from the cylinder or whether he has some sort of 'clever change-over system', and nor am I sure whether his shower can be supplied from the cylinder.

This is a very difficult subject. I had been told for years, cheaper to heat DHW with gas to electric, and I never questioned it. In the main as near impossible to measure, the gas boiler could modulate, so run times tells you nothing, and the immersion heater was powered from a FCU so not easy again to measure, so just accepted what I had been told.

But in this house the oil boiler does not modulate, so rated at 20 kW so if it runs for 20 minutes, then 20/3 = approx 7 kWh and I needed to run it once a day, so 50 kWh per week, and the iboost+ shows how much used per week, so know it uses around 15 kWh per week, so at 8.5p/kWh electric night rate v 5p/kWh oil, electric is cheaper than oil, plus electric is thermostatically controlled, so no worries about legionaries, and I have an oil tank filled once a year instead of twice a year.

The costs will vary from home to home depending on pipe runs, and where the boiler is. But move from stored water to instant water heating, and we are now looking at the cost of the match. What it costs to fire up the boiler, even if only a cup full of water used. How many times a day are we heating up a heat exchanger? This

shows two gas boilers, the 8 - 18 is size in how much gas it uses, not the size of storage tank, convert to kWh and 16KW/20KW/24KW/32KW/36KW depending on model, but designed to be right next to the shower in same way as instant electric showers. Being close to the shower will mean very little cold water needs to be run, and I am sure it will be cheaper to run to instant electric. But the second one also does central heating, and supplies multi-outputs. A shower likely runs for at least 15 minutes, so gas far better, but the hand wash basin maybe 1 minute, and this is where the losses mount up.

Then I would suggest your expectations, are clouded by what you are accustomed to in your own home. The major complaint from combi owners, is the delay involved, before heated water appears out of the combi.

This is a very good point, we only tend to look at our own homes. My boiler is a floor below any of the taps I normally use. And two floors below the hot water tank.

 

[Harry Bloomfield]

But the second one also does central heating, and supplies multi-outputs. A shower likely runs for at least 15 minutes, so gas far better, but the hand wash basin maybe 1 minute, and this is where the losses mount up.

One of the problems with combi-boilers, the other being that a combi, to be able to satisfy the demand for the hot water to be instantly heated, it needs to be much higher Kw rating, than it would be to just serve CH, plus heating a cylinder.

 

[JohnW2]

This is a very difficult subject. I had been told for years, cheaper to heat DHW with gas to electric, and I never questioned it.

Yes, it is not a totally straightforward business.

The costs will vary from home to home depending on pipe runs, and where the boiler is. But move from stored water to instant water heating, and we are now looking at the cost of the match. What it costs to fire up the boiler, even if only a cup full of water used. How many times a day are we heating up a heat exchanger?

Then I would suggest your expectations, are clouded by what you are accustomed to in your own home. The major complaint from combi owners, is the delay involved, before heated water appears out of the combi.

This is a very good point, we only tend to look at our own homes. My boiler is a floor below any of the taps I normally use. And two floors below the hot water tank.

Yes, I think we're all agreed about that. For what it's worth, my personal experience of 'average' homes with stored hot water is that there are usually quite significant delays before hot water appears at taps and showers - delays which do not feel (to me) to be any less than those I experience in (generally fairly small) homes with combis.