Linking Two Unvented Cylinders

[Dragoon]

Hi looking for some help please.

Need a plumber to install heating and hot water from scratch in a new-build. I want to go a bit flash and install a round bath. The bath holds 405 litres of water. I also have a steam shower cabin to install which has about a zillion shower jets. The rest of the house is pretty normal.

The problem is that my unpredictable girlfriend may want to run a bath while I’m having a shower (also a friend who may be staying may want to do some washing up at the same time). Point is that I would like to avoid any sort of loss in hot water flow if possible.

So realistically Combis are not really viable. So a system boiler with an unvented cylinder would be the choice to go for.

However as the large bath would only be used very occasionally, it would be a waste of energy having to constantly heat up a large cylinder to provide for the occasional use of a large bath.

So my question is, is there any way of linking up two smaller unvented cylinders so that only one is heated and the other can be heated when the large bath needs to be run?

 

[chris watkins]

However, as you said before, filling a bath would be 60(hot):40(cold) so for a 400ltr bath I would need 240 ltrs hot water which, at 12 ltrs/min would take 20 mins.
Is 20 mins okay to fill a bath? I don't really have baths often so I wouldn't know. This is really just for the girlfriend!

The 60/40 bit only works if hot is around 60 - 65 & cold is around 10deg C the blend would give hot water at around 40. With a combi (instantaneous heater) the power is fixed (say 28kW) & the flow rate can be adjusted to give the require outlet temperature. So increase the flow & outlet temp goes down, slow it & it increase (it is said to be proportionate).
Most manufacturers state the flow rate with a 35deg rise, so if incoming mains water is at 10 deg C the outlet temp would be 45 with a flow rate of 12L/M.

45 is little more than hand hot so by the time it gets to said bath & heats up the material, sits around for half hour it all equals a cold bath.

 

[Gray0689]

Thermal store for your situation is not a good idea
They are ok for a solid fuel link up just about IMHO

 

[AWheating]

400ltr bath, minus the volume of the two people enjoying each others company.

may even increase the water temps........

 

[Dragoon]

The energy losses of a good unvented cylinder are 1.5 - 2.5 kWh's per day. Ie naff all. You are worrying over nothing, or pennies per day.

:welcome:

Hi Nostrum.

Thanks for putting some sort of a figure on the losses for me. If it only amounts to just pennies a day, it’s not really worth compromising on flow rates.

Also the system will be housed in a dedicated small boiler room, which I intend to also use as a largish airing cupboard. And any heat losses from that will go to heat the hall so really the losses will be almost negligible.

Oh and thanks for the welcome!

 

[Best]

You could also make sure the pipes are well insulated at the unvented unit - especially the hot supply pipe leaving the top of the cylinder. If that pipe drops downwards, it will prevent heat gravitating up the pipe. Small savings, but still helps.
Also get rid of any women from your house. :smile:

 

[Dragoon]

The 60/40 bit only works if hot is around 60 - 65 & cold is around 10deg C the blend would give hot water at around 40. With a combi (instantaneous heater) the power is fixed (say 28kW) & the flow rate can be adjusted to give the require outlet temperature. So increase the flow & outlet temp goes down, slow it & it increase (it is said to be proportionate).
Most manufacturers state the flow rate with a 35deg rise, so if incoming mains water is at 10 deg C the outlet temp would be 45 with a flow rate of 12L/M.

45 is little more than hand hot so by the time it gets to said bath & heats up the material, sits around for half hour it all equals a cold bath.

Hi Chris.

Thanks for that, I never did understand the 35deg rise as quoted by boiler companies, now I do. So that’s why Ray suggested that the cylinder should feed the bath and the combi should feed the shower and the rest.

So do you think I should just stick with a system boiler with an unvented cylinder? As Nostrum suggested that I’m worrying over nothing and that the energy losses will not really amount to that much, just pennies a day?

 

[Dragoon]

You could also make sure the pipes are well insulated at the unvented unit - especially the hot supply pipe leaving the top of the cylinder. If that pipe drops downwards, it will prevent heat gravitating up the pipe. Small savings, but still helps.
Also get rid of any women from your house. :smile:

The place is a bungalow on just the ground floor, so the pipe leaving the top of the cylinder will probably have to drop downward at some point.

Also I've tried doing without the women before. . . . . . but it's not good for the ol' eye sight. . . . if you know what I mean!:chinese:

 

[Dragoon]

400ltr bath, minus the volume of the two people enjoying each others company.

may even increase the water temps........

Well that was the idea behind the large bath, but judging from previous attempts, the increase in the water temp was quickly counteracted by the coldness of a shoulder which she offered, before going back to reading her book! :disappointed:

 

[Dragoon]

Thermal store for your situation is not a good idea
They are ok for a solid fuel link up just about IMHO

Hi Gray.

I actually like the idea of the way Thermal Stores work, it's almost like a large powerful Combi. However I don't know anyone who has one installed, and from the net the picture I get is that they can be temperamental, so some people really hate them while others rave about them. And like you said I don't think it's a good idea for my situation.

 

[SimonG]

Theres nothing temperamental, special or complicated with a thermal store. Without having multiple inputs though it will cost you an arm and a leg maintaining sufficient temperature in the thermal store for your requirements.

 

[Dragoon]

Theres nothing temperamental, special or complicated with a thermal store. Without having multiple inputs though it will cost you an arm and a leg maintaining sufficient temperature in the thermal store for your requirements.

I did my research on thermal stores a couple of years ago, but I remember vaguely something about issues with the mixing with cold water after the hot water's come through from the heat exchanger. Also heat exchanger problems as well, but the ol' memory's not too good so couldn't say for certain. But I do remember being impressed by them!

 

[Best]

Stainless Steel unvented cylinder = hot water up to as much as 65 degrees at usually 3bar pressure & full flow of your pipe work. Nothing really competes with that - & a powerful whole house pump costs a lot & is mechanical, so it won't last forever & it makes a noise.

 

[SimonG]

I did my research on thermal stores a couple of years ago, but I remember vaguely something about issues with the mixing with cold water after the hot water's come through from the heat exchanger. Also heat exchanger problems as well, but the ol' memory's not too good so couldn't say for certain. But I do remember being impressed by them!

Horses for courses, but I dont think this is your horse

 

[Dragoon]

Stainless Steel unvented cylinder = hot water up to as much as 65 degrees at usually 3bar pressure & full flow of your pipe work. Nothing really competes with that - & a powerful whole house pump costs a lot & is mechanical, so it won't last forever & it makes a noise.

Hi Best.

Yeah thats what the original idea, and I think I'm slowly coming back to that again. It's tried and tested! And it works! And all plumbers are familiar with it! And it's hot enough not to be dampened by a cold shoulder! :yes:

 

[Micksta]

Im Probably to late but have you thought about a Worcester Bosch high flow 440, works on the same principle as a Combi but slightly different.

 

[Dragoon]

Hi Micksta.

Sorry for the late reply. Just got very busy with other things recently.

I’ve had a look at the Hightflow 440, but it looks like another combi to me. How is it slightly different?

I’ve kind of discounted combis now, and am looking just for regular unvented cylinder with system boiler.

I asked a couple of cylinder companies about linking two cylinders (to save on fuel consumption), and it certainly can be done (according to them). However after considering it at some length, I’ve abandoned the idea because:

My main worry is that if the thing ever goes wrong, I just want to be able to call up the first available plumber to fix it. However if the installation is a little complicated, that may be a problem.

Also I’d have to sort some way to combat the legionnaires problem for the cylinder that’s not used as much.

So just gonna go with a standard unvented cylinder with a system boiler. And since I’d be just topping up the heat inside a well insulated cylinder the running costs shouldn’t be too nightmareish!! . . . . . . hopefully!

 

[drip-dry]

Hi Micksta.

Sorry for the late reply. Just got very busy with other things recently.

I’ve had a look at the Hightflow 440, but it looks like another combi to me. How is it slightly different?

I’ve kind of discounted combis now, and am looking just for regular unvented cylinder with system boiler.

I asked a couple of cylinder companies about linking two cylinders (to save on fuel consumption), and it certainly can be done (according to them). However after considering it at some length, I’ve abandoned the idea because:

My main worry is that if the thing ever goes wrong, I just want to be able to call up the first available plumber to fix it. However if the installation is a little complicated, that may be a problem.

Also I’d have to sort some way to combat the legionnaires problem for the cylinder that’s not used as much.

So just gonna go with a standard unvented cylinder with a system boiler. And since I’d be just topping up the heat inside a well insulated cylinder the running costs shouldn’t be too nightmareish!! . . . . . . hopefully!

Well if.you have room for the storage tanks ...most plumbers would say you have made the right chose..

 

[Micksta]

Well if.you have room for the storage tanks ...most plumbers would say you have made the right chose..

Correct if I had the choice I would go mains fed cylinder every time, good pressure, quick heat recovery, cheap to run, put in a hot water return this will cut down on the water siting still and cut down the legionnaire thing.

 

[Micksta]

Hi Micksta.

Sorry for the late reply. Just got very busy with other things recently.

I’ve had a look at the Hightflow 440, but it looks like another combi to me. How is it slightly different?

I’ve kind of discounted combis now, and am looking just for regular unvented cylinder with system boiler.

I asked a couple of cylinder companies about linking two cylinders (to save on fuel consumption), and it certainly can be done (according to them). However after considering it at some length, I’ve abandoned the idea because:

My main worry is that if the thing ever goes wrong, I just want to be able to call up the first available plumber to fix it. However if the installation is a little complicated, that may be a problem.

Also I’d have to sort some way to combat the legionnaires problem for the cylinder that’s not used as much.

So just gonna go with a standard unvented cylinder with a system boiler. And since I’d be just topping up the heat inside a well insulated cylinder the running costs shouldn’t be too nightmareish!! . . . . . . hopefully!

Correct if I had the choice I would go mains fed cylinder every time, good pressure, quick heat recovery, cheap to run, put in a hot water return this will cut down on the water siting still and cut down the legionnaire thing.

 

[Gray0689]

Secondary return only if very long pipe runs

 

[Ch4 plumbing]

Secondary return only if very long pipe runs

And on a timer and lagged.

 

[Gray0689]

And on a timer and lagged.

And sized correctly but only really cost effective in a large house

 

[Micksta]

And sized correctly but only really cost effective in a large house

Correct, but still worth while.

 

[Worcester]

For cylinders, consider the Joule Eco - extra insulation, water kept warm and cosy, even less heat loss.
Insulate all pipes - the 'boiler room' shouldn't be warm that's just bad installation/ insulation.
On our installs we are having to install small rads in airing cupboards for people as our buffers, thermal stores, DHW cylinders and pipework is so well insulated. - We even insulate the primaries from the heat source to the DHW cylinder, as well as the DHW distribution pipes - remember any DHW secondary returns should also be insulated.

Insulation will ALWAYS pay you back on running costs.