Help: Boiler timer set-up for boiler, tank & cylinder

[larrens]

I have a hot water system that is quite old (15 years or more apparently) & seems to be costing me a lot of money in gas bills. I am not exactly sure how it works or links together.

I would be grateful if someone could guide me in making the most cost efficient use possible of this system from a hot water point of view. I am not worried about central heating at this stage.

I live in rented accommodation, so whilst the boiler is old & inefficient, its not up to me to update it, so at the moment I simply need to live it.

I in my previous house, I had a combi-boiler that provided hot water on demand.

My current house does not have on demand hot water.
I have a boiler, connected to an electronic timer. There is a water tank in the loft & a hot water cylinder in un upstairs cupboard. (I believe this has an immersion heater but it is currently off)

I need to have hot water in the morning, between 6:30am & 9am. My wife & I are at work during the day. We then need hot water again when we get home from work, around 6pm - 11pm.

Currently, the boiler timer is set to go on at 5am & only turn off at 23:30pm, so its on all day covering the hours above which is when I need it. I realise its not actually heating the water continuously, as it gets stored in the hot water tank.

My questions are:
1) should I leave the time as is
2) should I set the timer for the morning & then again at night & if so, how long before I need the hot water must the boiler go on. Similarly, can I turn the boiler off before 23:30 if hot water is being heated & stored earlier on for the bath at 23:00? Someone once said this is not the best option because during the day the water in the tank will cool & use a lot more gas to start heating so much more up again in the evening

Thanks

 

[D_Hailsham]

My questions are:
1) should I leave the time as is
2) should I set the timer for the morning & then again at night & if so, how long before I need the hot water must the boiler go on. Similarly, can I turn the boiler off before 23:30 if hot water is being heated & stored earlier on for the bath at 23:00? Someone once said this is not the best option because during the day the water in the tank will cool & use a lot more gas to start heating so much more up again in the evening

Need to know the answer to these questions first.

1. What insulation is there round the hot water cylinder? A loose jacket or solid foam attached to the cylinder?

2. Does the timer allow you to set separate hot water and heating times?

3. Can you set more than one ON period over a 24 hour period?

4. Is there a thermostat on the side of the hot water cylinder? If not, how is the hot water temperature controlled?

 

[larrens]

Hi D_Hailsham - thanks for the reply

Answer to your questions:

1. What insulation is there round the hot water cylinder? A loose jacket or solid foam attached to the cylinder?
There is a loose jacket, tied around the cylinder

2. Does the timer allow you to set separate hot water and heating times?
Yes it does

3. Can you set more than one ON period over a 24 hour period?
Yes, I can set 2 ON periods

4. Is there a thermostat on the side of the hot water cylinder? If not, how is the hot water temperature controlled?
I am not sure, I have never noticed a thermostat & will take a look this evening. There is supposed to be an immersion heater, but I think this is off all the time.

 

[larrens]

Hi

I took a close look at the water cylinder - I could not see a thermostat on it so I am not sure how the temperature is controlled, it could be under the insulating jacket which I can't remove - I can see a wire going into the top of the cylinder which I assume is the immersion heater, but as I said earlier I think this is left off.

Thanks

 

[Agile]

It sounds as if its a gravity system which is very inefficient. If thats the case then it will have 28mm heating coil pipes.

It will always be inefficient and slow to heat up.

But to make the best of a bad system, I suggest you set the hot water to be heating for one hour before you want to use hot water and only continue it until 30 minutes after the water is used.

Tony

 

[D_Hailsham]

There is a loose jacket, tied around the cylinder.

That's a pity. The loose jackets are nothing like as good an insulator as the polyurethane ones which are attached when the cylinder is manufactured; this means the cylinder will loose heat fairly quickly. Obviously a new cylinder which meets current Building Regs is the ideal, but it's unlikely you will be able to persuade your landlord to install one. So the next best thing is to buy a second jacket from B&Q/Wickes etc and put it over the existing jacket. Make sure there are no gaps where you can see the cylinder.

Timer
If the HW times can be set completely separately from the CH times, that will be very useful. But if it's a case of HW only (Summer) but CH and HW together (Winter), it means you have a pumped heating/unpumped hot water system, which is not so efficient as a fully pumped system.

Yes, I can set 2 ON periods

Then you could set the HW to come on before you wake up; off when you leave for work; on about an hour before you get back home; and off when you go to bed.

I am not sure, I have never noticed a thermostat & will take a look this evening.

I took a close look at the water cylinder - I could not see a thermostat on it so I am not sure how the temperature is controlled, it could be under the insulating jacket which I can't remove - I can see a wire going into the top of the cylinder which I assume is the immersion heater, but as I said earlier I think this is left off.

If there was a thermostat hidden under the jacket, you would see a wire coming out from the jacket. The wire into the top will be the immersion heater. Sometimes there is a thermostatic valve on one of the pipes going into to side of the cylinder, which controls the HW temperature.

If there is neither a thermostat attached to the cylinder nor a thermostatic valve on the pipe, the water temperature will depend on the boiler temperature.

So my suggestions are:

1. Put a second jacket round the cylinder

2. Set timer for HW in the morning and then in the evening. There is no need to have it on all the time you are in the house. For example you may be able to turn it off before you leave for work; just depends on how much water is used. Some goes for the evening; the best off time will depend on when you have your baths/showers etc.

3. Initially allow half an hour to heat up and increase if necessary.

Anything else will require a change to the heating system, which is the landlords responsibility.

I agree, in general with Tony's view that it is probably a "gravity" system (pumped heating/unpumped HW. However I do not see the point in heating the water for 30 minutes after you have stopped using it. Depending on how hot the water is initially and how much is used, it may even be possible to turn it off well before you leave for work or go to bed.

One final suggestion. If you have a washing machine or dishwasher which uses hot and cold fill, change it to cold fill only. You can buy a Y adapter to do this. The two hoses attach to the Y adaptor which then connects to the cold supply. Your machine will be more efficient and you will also save gas.

 

[Agile]

My reason for leaving it on for 30 minutes after the water is used up is to half reheat it.

Since heat loss is proportional to the temperature difference then the heat loss will be smaller and it will then be half heated at the next reheat. Furthermore if hot water was used then it would be luke warm.

I have assumed that a bath will mostly deplete the cylinder.

Tony

 

[D_Hailsham]

My reason for leaving it on for 30 minutes after the water is used up is to half reheat it.

That might be OK if you have a well insulated cylinder with 50mm or more of polyurethane. But the OP only has a loose jacket, which is often not much better than no jacket at all.

In any case, even if you only half reheat the cylinder, say to 40C, by the time you want hot water in the evening or next morning it will probably have lost all the heat put into it. So you have heated up the water unnecessarily.


The water temperature has to drop a lot before it can be considered lukewarm. Most of the time you need to mix cold with hot to get a usable temperature for washing etc.

 

[Agile]

The heat loss from 35° will be quite slow and it will still be warm to wash hands or the washing machine.

Doing that will save reheat time later and in the meantime give warm water for washing hands.

Tony

 

[larrens]

Thanks for the adice & excuse my ignorance, but if the hot water stays off the whole night & the water in the cylinder cools down, what happens in the morning when the water is heated up & fed into the hot water tank.

Does the hot water not then mix with the cold water already in the cylinder to make a warm mix, or does the cold water get pushed out & replaced with the hot water?

 

[D_Hailsham]

Thanks for the adice & excuse my ignorance, but if the hot water stays off the whole night & the water in the cylinder cools down, what happens in the morning when the water is heated up & fed into the hot water tank.

Does the hot water not then mix with the cold water already in the cylinder to make a warm mix, or does the cold water get pushed out & replaced with the hot water?

There are two completely separate lots of water!

The cylinder has a copper coil inside which connects to the boiler - you will see two pipes coming out of the side of the cylinder at the bottom and about halfway up the side. The rest of the cylinder contains the water which comes out of your hot taps. There will be a pipe going into the bottom of the cylinder which goes up into the loft, where it connects to the outlet of the cold water tank. At the very top of the cylinder there will be a pair of pipes joined as a T on its side. The pipe going up into the loft is a safety pipe which hangs over the cold water tank - it's there in case the water in the tank boils over. The pipe coming out horizontally from the T junction is the hot water supply to the taps.

When the water in the main body of the tank needs to be heated up the boiler will come on and circulate hot water through the copper coil in the cylinder, which will then heat the water in the cylinder.

No water leaves or enters the cylinder when it cools down or heats up; the only time this happens is when you turn on a hot tap.

The pressure of the water in the cold tank (due to the height of the tank above the tap) is sufficient to force hot water out of the cylinder, through the pipe and out of the tap. The hot water is replaced by cold water from the tank in the loft. Obviously as more hot water is used and replaced by cold water, the temperature of the water in the cylinder will reduce, and eventually need reheating.

 

[vulcancontinental]

Agile wrote
"Since heat loss is proportional to the temperature difference then the heat loss will be smaller and it will then be half heated at the next reheat."

Yes but a loss is a loss and a loss over a longer period is probably worse than a loss over a shorter period of pre-heat and immediate use in the morning.

D.Hailsham wrote

"Furthermore if hot water was used then it would be luke warm. One final suggestion. If you have a washing machine or dishwasher which uses hot and cold fill, change it to cold fill only. You can buy a Y adapter to do this. The two hoses attach to the Y adaptor which then connects to the cold supply. Your machine will be more efficient and you will also save gas."

Er, I'm not convinced on this either. The cost of a KW of electricity is greater than the equivalent net KW of gas. 80% of the energy used in a washing cycle is heating the water, that's why cool fill machines are becoming prevalent.

Cold washing is supposed to be the equal of hot wash but years ago the electricity and gas companies and the major soap company's decided hot washes were better because
1: They use energy which is what the gas and electric companies wanted to sell. It was impossible to buy a cold fill machine in gas or electric showrooms.
2: Soap powder has to be made with expensive chemical plant while the liquid soaps used in cold washes could be knocked up in a competitors shed. So the two big soap powder companies could retain their market they discouraged the supermarkets from stocking and selling liquid soaps.

Lastly, If you're running a washing machine on a hot water supply from a cylinder some distance away, let the cold out through a nearby tap first otherwise the machine is heating the cold water with electricity first and just when the hot from the cylinder get there the machine shuts off.

More than you ever needed or wanted to know about the economics of a washing machine and I'm almost embarrassed to know it.

 

[D_Hailsham]

D.Hailsham wrote

"Furthermore if hot water was used then it would be luke warm."

It's a good thing Agile and I are not naturally litigious or you would be sued for libel! Agile said this, not me.

One final suggestion. If you have a washing machine or dishwasher which uses hot and cold fill, change it to cold fill only. You can buy a Y adapter to do this. The two hoses attach to the Y adaptor which then connects to the cold supply. Your machine will be more efficient and you will also save gas.

Er, I'm not convinced on this either. The cost of a KW of electricity is greater than the equivalent net KW of gas. 80% of the energy used in a washing cycle is heating the water, that's why cool fill machines are becoming prevalent.

You get better control over the water temperature using cold fill only. If you have a mixed fill with hot going in at about 60C and cold at about 15C and want a temperature of 40 or 50C you have to fill with both hot and cold to get a temperature lower than required, then heat it up to temperature.

Cold washing is supposed to be the equal of hot wash but years ago the electricity and gas companies and the major soap company's decided hot washes were better because
1: They use energy which is what the gas and electric companies wanted to sell. It was impossible to buy a cold fill machine in gas or electric showrooms.
2: Soap powder has to be made with expensive chemical plant while the liquid soaps used in cold washes could be knocked up in a competitors shed. So the two big soap powder companies could retain their market they discouraged the supermarkets from stocking and selling liquid soaps.

It was, and still is, due more to users' reluctance to believe that cold washes will do just as good a job as hot ones. My mother (long gone now) would wash everything at the same high temperature in the belief that you would not get the dirt out with a colder wash. Cold fill washing machines and cold temperature detergents have standard in Germany for years.

 

[vulcancontinental]

Oops, I'll mind my P and Q's.

that's interesting about the blend as I (probably wrongly) thought the machine would fill from the hot and heat it up if necessary and with cool washes that would be less than 60C. Perhaps I gave the machines more flexibility and functions than they have and they take what's coming in from both then heat the mix. That does sound logical. Most do seem to be cold fill now anyway.

Not only in Germany but much of the world. Cool Force was the only liquid I recall and haven't seen that for a while but then again I don't do the washing. Used to do all the dust sheets cold but wife wouldn't trust cold wash for my socks and underwear - probably very wise too although I still have no friends. Say Nothing