Increasing amount of hot water from immersion heater

[Little Clanger]

I've got a 1050x450mm hot water cylinder with a single, straight, 30" immersion heater mounted in the top. The thermostat is, of course only 18". I would like to get more of the cylinder heated overnight on Economy 7.

 

There is an 8mm thermostat pocket sited more or less where the immersion ends - a little above it, as far as I can work out. Would it be OK to remove the 18" thermostat from the immersion and instead wire it to a short thermostat in the pocket? I'm assuming that would give me more hot water overnight, but would the water at the top of the cylinder get too hot if the low-mounted thermostat was set at, say 65 degrees?

 

Thanks

[SteamyTea]

I have E7, but a proper 200 lt cylinder with a lower element and thermostat as well as a top element and thermostat.  I think yours is about 140 lt.

 

Have you tried changing your DHW usage regime i.e. use it up in the morning, rather than last thing at night.  Use less water.

You may well find that the standing thermal losses are quite high, and get higher when you increase the temperature.

Adding extra insulation to the cylinder will help, as will lapping the pipework.

 

Apart from increasing the losses with a higher temperature, you increase the risk of scalding/boiling, which can cause other problems i.e. hot water going to the F&E tank, thermal protection cutting in, thermal protection valve opening.

[Little Clanger]

14 hours ago, SteamyTea said:

I have E7, but a proper 200 lt cylinder with a lower element and thermostat as well as a top element and thermostat.  I think yours is about 140 lt.

 

Have you tried changing your DHW usage regime i.e. use it up in the morning, rather than last thing at night.  Use less water.

You may well find that the standing thermal losses are quite high, and get higher when you increase the temperature.

Adding extra insulation to the cylinder will help, as will lapping the pipework.

 

Apart from increasing the losses with a higher temperature, you increase the risk of scalding/boiling, which can cause other problems i.e. hot water going to the F&E tank, thermal protection cutting in, thermal protection valve opening.

Thanks for your reply and advice.

I've got a jacket on the cylinder in addition to the sprayed on foam insulation.

What temperature do you have your two thermostats set at?

I've struggled to find any clear data on the temperature difference between the upper and lower areas of a hot water cylinder.

I suppose another option would be to have a pump circulating the water from top to bottom of the cylinder, the pump only switching on during cheap rate time.

[SteamyTea]

1 hour ago, Little Clanger said:

I've got a jacket on the cylinder in addition to the sprayed on foam insulation

I basically filled my airing cupboard up with insulation.

1 hour ago, Little Clanger said:

What temperature do you have your two thermostats set at?

Lower thermostat is set so the top of the cylinder is 50°C. The upper thermostat is set to 55°C, but I very really use it.

 

1 hour ago, Little Clanger said:

I've struggled to find any clear data on the temperature difference between the upper and lower areas of a hot water cylinder

Somewhere on here I posted up a chart showing my mean positional temperatures.

Here it is.

 

 

1 hour ago, Little Clanger said:

suppose another option would be to have a pump circulating the water from top to bottom of the cylinder

I thought about this but, for me, it is not worth it, and would only store a small amount of energy anyway.

 

I am a pretty unique case as I rough it on my own, so can put up with a bit of a short shower, or Luke warm bath occasionally.

As I am constant trying to save energy, without large capital expenditure, I look at cheap options.

I have secondary timers fitted to all three E7 circuits that limit the run time.

I have just reset my hot water timer to come on at 4AM and off at 6AM. This will limit the storage to 6 kWh and should give me a bathful in the morning (at about 6AM) without any reheating, which for me, is wasted as losses.

I do similar with the storage heaters as I like it warm when I get up, so no point them reaching maximum capacity at 4AM, then cooling, then reheating.

I effectively have E4.

Just had my water bill in and in the last 90 days have used 20m³. Which is way too much (220 lt/day). Last year I used a lot less, almost half, but it was a strange year last year as I was away a lot more).

 

I justify my high usage as my body aches a lot and no one wants to see a grubby chef, in grubby clothes.

[Little Clanger]

Thanks, SteamyTea.

Very interesting

[marshian]

We have a 114 Litre tank (Ish) we heat water once a day between 7am and 8am to around 50 deg (this fluctuates a bit because the water heating is timed rather than to a set temp point) 

 

This gives us enough water for 2 showers AM and 2 showers PM - I have data logging temp sensor at top of tank and another at the bottom

 

However this means our graphical representation looks a little weird but fundamentally once the morning showers are done the water at the bottom of the tank is replaced with water from the cold store in the loft above

 

Our energy usage in summer for water heating is much lower than the winter where the cold store tank (cold loft) is at a much lower temp

 

[SteamyTea]

5 hours ago, marshian said:

Our energy usage in summer for water heating is much lower than the winter where the cold store tank (cold loft) is at a much lower temp

Mine as well.

Kind of a poor man's solar thermal.

[ProDave]

Best upgrade you could do is an unvented cylinder which generally are better insulated than the simple spray foam vented sort, and one with proper horizontally mounted immersion heaters usually one at the bottom and one mid way up.  The top entry immersion heaters are nothing but trouble.

[marshian]

1 hour ago, SteamyTea said:

Mine as well.

Kind of a poor man's solar thermal.

 

I think of it like that too - Loft temp in the spring/summer/autumn in daylight hours can regularly be above 30 Deg C for most of the day and has occasionally hit low 40's

 

I have a data logger recording temp and humidity up there because I was concerned about pipes freezing in the winter after I moved the cold water tank to a better location and increased the length of all the pipework by 3m

 

This winter (when temps are cooler) the plan is to increase the level of insulation up there which will lower the cold temps further

[John Carroll]

On 31/08/2024 at 17:43, Little Clanger said:

I've got a 1050x450mm hot water cylinder with a single, straight, 30" immersion heater mounted in the top. The thermostat is, of course only 18". I would like to get more of the cylinder heated overnight on Economy 7.

 

There is an 8mm thermostat pocket sited more or less where the immersion ends - a little above it, as far as I can work out. Would it be OK to remove the 18" thermostat from the immersion and instead wire it to a short thermostat in the pocket? I'm assuming that would give me more hot water overnight, but would the water at the top of the cylinder get too hot if the low-mounted thermostat was set at, say 65 degrees?

 

Thanks

 

The problem with top mounted elements IMO is that they heat the water uniformly in a stratified state  so if say the top 20L or so of water is at 40C and the remainder is at 20C then the 20C remaining water will only have reached 40C and that top 20L will have reached 60C, the normal stat which measures the average temperature of the water its immersed in will not switch off until the average temperature is 60C so that top 20L may become very hot, the cylinder will heat perfectly uniformly  if all the cylinder volume is at the same temperature, your proposed stat location could  result in a even higher temperature gradient as its only measuring the water in the cylinder bottom.

If the cylinder has no heating coil then you should be able to install a 36" immersion which should give you a extra 20L or so of hot water.

Edited September 2 by John Carroll

[G and J]

4 hours ago, ProDave said:

Best upgrade you could do is an unvented cylinder which generally are better insulated than the simple spray foam vented sort, and one with proper horizontally mounted immersion heaters usually one at the bottom and one mid way up.  The top entry immersion heaters are nothing but trouble.

Would I be correct in inferring that the main benefit from a pressurised system comes from the quality of the tank? If so I could use a pressurised tank but on gravity.  🙂

[JohnMo]

7 hours ago, G and J said:

Would I be correct in inferring that the main benefit from a pressurised system comes from the quality of the tank?  🙂

Unvented - high water flow rates equal to cold water. So you have decent showers, not long to wait for water to hit the tap, way quicker than a combi. It's also hygienic water, exact same quality as cold tap water. Way more hot water for the same cylinder size when compared to a thermal store.

 

Vented - rats or other animals drowning in the loft tank, making unvented cylinder not fit to consume. Low quality shower experience unless you add more pumps. Bigger thermal losses as you have a vertical pipe coming out the top connected to the loft tank.

[billt]

48 minutes ago, JohnMo said:

Vented - rats or other animals drowning in the loft tank, making unvented cylinder not fit to consume.

 

Utter rubbish. An unvented system installed to the water regulations has no route for animals or insects to enter the tanks.

 

Obviously an unmaintained system from the 1960s may have issues.

[JohnMo]

1 minute ago, billt said:

Utter rubbish. An unvented system installed to the water regulations has no route for animals or insects to enter the tanks

That's basically what I said, unvented is hygienic water, vented may not be, is unlikely to be, you would want to drink it.

[billt]

3 hours ago, JohnMo said:

That's basically what I said, unvented is hygienic water, vented may not be, is unlikely to be, you would want to drink it.

 

Sorry, you specifically said that vented water is unfit to consume because it has rats and other animals drowning in the tank. A system that is properly enclosed is a perfectly safe source of drinking water as it cannot have any wildlife in it.

 

The point is largely moot anyway as stored water is not generally used for potable water. Almost all houses that use stored water feed the kitchen tap directly from the mains supply.

[JohnMo]

5 minutes ago, billt said:

 

Sorry, you specifically said that vented water is unfit to consume because it has rats and other animals drowning in the tank. A system that is properly enclosed is a perfectly safe source of drinking water as it cannot have any wildlife in it.

 

The point is largely moot anyway as stored water is not generally used for potable water. Almost all houses that use stored water feed the kitchen tap directly from the mains supply.

Think you may be mixing up cold water and hot water, the discussion is about vented and unvented cylinders - all hot water will go to all sinks and outlets from the cylinder on a vented or unvented systems.

 

A vented system may have have a tight fitting lid on the loft tank, it also an open overflow. Doesn't get looked at from one year to the next, very few people will service a vented cylinder. I have fished out dead small animals - maybe not rat sized but definitely a rodent skeleton. On that occasion the lid was so distorted it would stay closed, have seen them with no lids.

 

I wouldn't have a vented system even they gave them away. 

[SteamyTea]

8 hours ago, JohnMo said:

Bigger thermal losses as you have a vertical pipe coming out the top connected to the loft tank.

UVC have a pipe coming out the top that goes to the expansion chamber.

 

I don't think the thermal losses need be any different in a proper installation.

 

I have never had a UVC, but have had combis, and they have been rubbish.

 

With a vented system you do not need them signed off for building control or insurance.

[marshian]

16 minutes ago, SteamyTea said:

UVC have a pipe coming out the top that goes to the expansion chamber.

 

I don't think the thermal losses need be any different in a proper installation.

 

That expansion pipe is full of water until it rises above the level of the cold store

 

(Funny story I know this becuase I wasn't thinking straight one day and cut into it to change it's route without drain down - luckily I had a bucket nearby and some self amalgamating tape to temporarily cover my error)

 

Anyway heat rises and it will be a source of losses (I am very tempted to fit a london loop in mine to see if it makes any difference)

[SteamyTea]

12 minutes ago, marshian said:

I am very tempted to fit a london loop in mine to see if it makes any difference

Not sure if that is sensible from a safety perspective.

The idea is that overheated water, or steam even, can easily vent away.

 

There is probably not enough water in the pipe to loose much via convection currents.

Realistically, the largest thermal losses are down the drain.

[JohnMo]

33 minutes ago, SteamyTea said:

UVC have a pipe coming out the top that goes to the expansion chamber.

No, the expansion is on the cold side of the system connected to the inlet group. My hot pipe goes up 50mm, horizontal for 300mm and then down. To minimise those pipe losses.

[SteamyTea]

1 minute ago, JohnMo said:

, the expansion is on the cold side of the system connected to the inlet group

That's interesting. The only installation I have looked at closely had the EV on the hit side, which I thought a bit silly.