Best way to heat a bath with electricity

[Harry Bloomfield]

In May 2018, I upgraded the 'supplementary insulation' (in addition to that on the cylinder itself) from about 200 mm (top, bottom and sides of cylinder) to some 400 - 600 mm, and that resulted in something like a 2-3 kWh/day per day reduction in energy usage.

There is little point in insulating the base of a cylinder, because the base will be full of cold water anyway - apart from for frost protection.

I have a yellow 120L cylinder, gas heated, but with an immersion heater for emergencies - but never needed to meet emergency needs in 40 years. I have some old bed quilts around and I wondering whether it might be worthwhile to use them as additional insulation around the cylinder?

 

[JohnW2]

There is little point in insulating the base of a cylinder, because the base will be full of cold water anyway - apart from for frost protection.

It's certainly the case that the bottom of the cylinder will benefit least from additional insulation, but that doesn't mean 'no benefit'. For a substantial number of hours each day (when the tank is 'full of hot water") when hot water is not being used (hence no cold water being drawn in), the bottom of my cylinder is pretty hot.

In any event, given that my cylinder is sitting on a slatted shelf some 600 mm or so above floor level, it seemed to make sense to also 'stuff that space with insulation' whilst I was doing the rest. It's in quite a large 'cupboard' (something like 1.8m x 1.8m and I simply stuffed the whole thing with whatever I had - primarily a mixture of fiberglass and mineral wool.

I have a yellow 120L cylinder, gas heated, but with an immersion heater for emergencies - but never needed to meet emergency needs in 40 years. I have some old bed quilts around and I wondering whether it might be worthwhile to use them as additional insulation around the cylinder?

I think that any additional insulation would probably be worthwhile. My (140 L) cylinder is about 35 years old, so probably not very well insulated itself, but there has always been about 200 mm of additional insulation around it. However, as I illustrated, increasing that from ~200 mm to about 600 mm resulted in an energy saving of about 33% - in mid-Winter from around 9 kWh/day to around 6 kWh/day.

Kind Regards, John

 

[ericmark]

My hot water tank is in the airing cupboard with cloths for airing all around it, never used the electric option, always heated with oil, the losses are more due to heat escaping from the pipes between boiler and tank, so set the times ½ hour 3 times a week in summer, off in winter as when central heating runs tank will warm up, no option to turn it off.

Clearly electric immersion heater only losses is from the tank. So may as well stay on 24/7 or for 7 hours if on cheap rate.

I know oil is cheaper than electric, but also more loses, so not sure which overall is cheaper. I know after the Ronan Point event resulted in many flats not being able to have gas heating, but this hardly applies to a bungalow, I suspect some do lack the room for the storage tank, but even had gas in the caravan, OK bottles did not last that long, the flame in the fridge could empty my bottle in three weeks.

I assume some medical reason why they need a bath rather than shower? But I had a Main 7 gas boiler in last house for domestic hot water, and it took an age to fill the bath, from memory around 20 minutes at 18 kW so an electric one would likely take an hour.

 

[JohnW2]

My hot water tank is in the airing cupboard with cloths for airing all around it, never used the electric option, always heated with oil, the losses are more due to heat escaping from the pipes between boiler and tank, so set the times ½ hour 3 times a week in summer, off in winter as when central heating runs tank will warm up, no option to turn it off.

...and, in any event, during Winter the heat 'escaping from pipees' is not 'wasted', anyway, since it just heats the house.

Clearly electric immersion heater only losses is from the tank. So may as well stay on 24/7 or for 7 hours if on cheap rate.

I'm not sure that I see the logic in that statement.

I know oil is cheaper than electric, but also more loses, so not sure which overall is cheaper.

I have no experience of oil - but, as above, 'losses' of heat are not an issue, since they merely contribute to heating of the house.

I assume some medical reason why they need a bath rather than shower?

I would think that there are few medical reasons for 'needing a bath' (rather than shower); even those who cannot stand can have showers with appropriate equipment - but I can think of some 'medical reasons' for having a shower rather than a bath,

Kind Regards, John

 

[DiyNutJob]

but I can think of some 'medical reasons' for having a shower rather than a bath,

You'd think people with medical reasons would be having a bed bath. I think people need to realise the good times are gone, and it isn't temporary. The way of life has to change.

 

[JohnW2]

You'd think people with medical reasons would be having a bed bath.

There are all sorts of shades of grey between 'being normal' (i.e. being able to have a bath or shower, by oneself, according to choice) and needing to be given a 'bed bath'. However, as I implied, I can think of far more situations in which (at least with standard facilities) in which a person could have a shower, but not a bath, rather than the other way around as suggested by eric.

There are many people who could not steep into a standard bath (at all, or without assistance) but who can easily enter a shower cubicle - and, if they had problems standing, can sit on a stool in the cubicle. Indeed, I'm sure that my wife, whose knees are a bit problematical, would struggle to get into a standard bath (without a fair bit of assistance) but has no problem showering.

I think people need to realise the good times are gone, and it isn't temporary. The way of life has to change.

Things have certainly changed, although the extent to which that represent a problem obviously varies between families. However, as I implied before, for those who are already struggling with energy prices and the cost of living in general, baths (no matter how the water is heated, but especially if it is by electricity) are an expensive 'luxury', which they really ought to forego.

In any event I suspect that relatively few people take baths regularly these days (showers instead), a situation very different from that in my youth. Furthermore, from the point-of-view of 'hygiene', baths have always been a bit suspect, since one's whole body wallows about in a single pile of water that has been in contact with every part of their body - and I've never heard of people 'rinsing themselves down' to get rid of that 'contaminated water' after theye have had a bath

Kind Regards, John

 

[ericmark]

With my C Plan I can't turn DHW off, as you say in Winter the pipe work results in UFH, but in summer don't really want to heat the house, I see no reason why we can't have a Sterling engine running off gas or oil, so it could drive a refrigeration unit, but if a electric heat pump is too expensive that would be clearly too expensive.

But 500 litres of 28 sec gas oil was £320 which will just about last the year for me in a three story house, so for a bungalow clearly cheaper, this does central heating as well as domestic hot water, clearly insulating the house better could reduce how much we use, but unlikely more than 20% more likely hard to better 10% so to get money back in a year, don't want to spend more than £50.

Fit one double glazed unit at 1" gap instead of ¼" gap will cost around £2000 easy to do the maths, simply not worth changing just for the thicker windows, maybe worth it to avoid painting the wooden frames, or where the wood has gone rotten, but not simply to make home more efficient.

At 72 maximum pay back time is 20 years, more like 10 years, as likely will need to move into a home before I die, the state will likely force me to sell house to pay for my care, and will take most of the money, my mother was allowed to keep £16k so why do anything to improve the home? We will not get the benefit, the state gets that.

 

[Harry Bloomfield]

I would think that there are few medical reasons for 'needing a bath' (rather than shower); even those who cannot stand can have showers with appropriate equipment - but I can think of some 'medical reasons' for having a shower rather than a bath,

When I recently had covid, I was taking a bath daily, instead of showers - the main reason for a how soak in a bath, being that it eased the aches and pains I was feeling as a result of the covid.

 

[SUNRAY]

10KW for 3mins or 3KW immersion for 20 mins... No contest. Even if it heats sufficiently in 20 mins.

Are you feeling alright?

Yes.

 

[SUNRAY]

20 kW = 86 amp, and my incoming supply is 60 amp, OK a heat pump may need less, but if I consider 40 amp for a shower, then I have 20 amp to spare, so 4.6 kW, maths shows it is simply not going to be enough. OK not a bungalow, it is a three story house, but electric heating is a non starter.

I believe we have a 60A fuse on a looped supply, I only shower and we have a 10.5KW shower unit (however we only use it on low power - 7KW). We also have a gas boiler and vented cylinder, Mrs Sunray is very effective at predicting how much to heat it.

My own tests with a 10KW shower and combi boiler on pre-pay meters show a 2 minute electric shower (typical for me) is cheaper and also uses less water than the combi. Even 6 mins but it's getting close by then. electric shower is way cheaper than combi bath.

 

[SimonH2]

Install an unvented hot water cylinder

Or a thermal store - which is better depends on many factors.
Thermal stores are particularly good if you have, or plan to have, multiple sources of heat - especially if one of those is an uncontrolled source such as a wood burning stove.

Although the hot water is stored, losses from a modern cylinder are tiny, nowhere near the massive waste from an ancient uninsulated copper cylinder.

I've mentioned this before.
It's 12 years or so ago now that I bought my second rental property. And at the time was fitting a thermal store into the first one (a flat). So while both were empty I did a little trial :
I left the thermal store being heated by the immersion heater, and after a day to settle down read the meter. After a couple of days I read the meter again - and simple maths gave me a standing loss of about 80W average.
In the house, I left the heating off and read the gas meter, then again after a couple of days. Again, simple maths (with help from the conversion factors on the gas bill) told me that the boiler was losing around 160W average to keep the hot water heat exchanger hot for that "turn on tap, get hot water quickly" feature - rather than "turn on tap, wait for up to a minute while it heats up" (there's even a special valve you can buy designed to restrict the water flow until it's hot and so optimise this stage !)
I think anyone who realised just how much gas was wasted* by the boiler would put it in eco mode to stop this behaviour. But it was interesting to get some numbers to counter the "thermal stores have to be inefficient due to heat losses" brigade.
Note that before lighting the flame, and after turning it off, gas boilers will run the fan to purge the combustion chamber of any residual "gasses that shouldn't be there". During these periods, it's effectively turning the main heat exchanger into a finned radiator actively transferring heat to the air that it's blowing out the flue. And running short cycles, like when just re-heating the small water content of the heat exchangers, will maximise these losses.

As an aside, at the time (Dec 2010) we were going through a very cold spell - down to -20 at times, barely reaching freezing during the short days. I also did a similar test running the heating off the immersion heater to find that the average heating load for the flat was about 2kW - under about the coldest conditions we ever see here. Contract with a combi with a minimum heat output of 9.5kW - so simultaneously both grossly oversized for the heating load, and significantly undersized for hot water (tenants weren't impressed by it's limited ability to fill a bath at a sensible rate).

In such a situation, one does not turn the water heating on ('from cold') immediately before one wants to take a bath - one heats up the water in the cylinder long before that - so that it is immediately available to fill a bath (as fast as the pipework and height of 'water head' {or pressure} will allow) when needed.

The common situation is that in which people want hot water to always be available (not just for baths), so their system is arranged such that the cylinder is always full of fairly hot water. However, if you want the cylinder only for filling baths, then you would simply need to switch the immersion on, say, 3 or more hours before you intend to take a bath (using a time switch to do that if necessary).

It used to be "a thing" to "put the water on" in preparation for the weekly bathtime, and it was left off the rest of the time - hence the number of houses where there's a prominent "IMMERSION" switch somewhere easy to see and access (such as in the kitchen). But these days we've got so used to hot water on demand that generally whatever source is used is left turned on all the time and simply maintains the tank of stored water by use of a thermostat.

...and, in any event, during Winter the heat 'escaping from pipees' is not 'wasted', anyway, since it just heats the house.

Exactly - something that the "efficiency police" seem to either fail to understand or (I suspect) deliberately ignore. Of course, in summer it is wasted energy, but in our house I'd say the heating is on at least some of the time for something like 9 months of the year. And it's not escaped some of us that there's a direct correlation between how much we use the lights, and how much we need the heating - so energy "wasted" by inefficient lighting isn't totally wasted (observation that we don't live on the ceiling where the hot air gathers is noted).

 

[JohnW2]

It used to be "a thing" to "put the water on" in preparation for the weekly bathtime, and it was left off the rest of the time - hence the number of houses where there's a prominent "IMMERSION" switch somewhere easy to see and access (such as in the kitchen).

Indeed so ... I remember that era well . However, as you go on to say ...

But these days we've got so used to hot water on demand that generally whatever source is used is left turned on all the time and simply maintains the tank of stored water by use of a thermostat.

... and that has come to be 'the norm' for a very long time.

The most 'inefficient' system of all (in Summer) is that seen in many hotels (and some very large houses) in which the hot water is continuously circulated arouynd 'loops', so that hot water is instantly available even at locations distance from the source/store of the hot water. However, as previously discussed, at times of year (or day) when space heating is required, the loss of heat from pipework with that system is merely one of the components of the space heating, not 'wasted'.

Kind Regards, John

 

[big-all]

i went to tenerife about 20 years ago and assumed the reason for the " avoid showering before 10.30 am " was because the demand may outstrip supply well yes it was not realizing all water was solar heated

 

[JohnW2]

i went to tenerife about 20 years ago and assumed the reason for the " avoid showering before 10.30 am " was because the demand may outstrip supply well yes it was not realizing all water was solar heated

Mind you, I suppose if they had water storage which was large enough and well-insulated enough, the guests could all have their showers early in the morning, using water that had been heated by the sun the previous day!

Kind Regards, John

 

[robinbanks]

large enough and well-insulated enough

I suspect the "well insulated" part is what is lacking; when there is bountiful energy supply to meet demand, one doesn't have to have much foresight