Having an unvented cylinder installed - do I need pressurised central heating?

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Adam Fell

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Ok here goes…..I moved into a house in January which has got a lovely new bathroom and nice thermostatic shower. The setup is a traditional vented system with a header tank in the loft and hot water cylinder in a cupboard in a bedroom. There is a pump in this cupboard that powers the shower to provide adequate pressure. The problem I have is that the pump is a cheap salamander one and makes a noise that measures 70dbs. This was installed in December (before we moved in) by a plumber who charged the previous occupiers £550. My understanding was that there was some problem with a pump in the loft. I contacted Salamander (I know pumps can be noisy but this is ridiculous) who said that it wasn’t installed correctly (too sharp bends, pipes going to and from different diameters). The plumber then stopped responding to me about this despite his work being covered for a year. Although frustrating, I don’t think it is worth me pursuing any further with either the plumber or Salamander.

The noise was fine when it was my wife and me, but we now have a baby that sleeps in this room and it is difficult to shower when it makes such a loud noise. There is now what seems to be airlock problems where it sometimes decides not to switch on which is rectified by turning on the handheld part of shower whilst it rests on the floor.

The installation of an unvented cylinder seems to be the most appropriate solution in my eyes for the below reasons
  • It will allow showers that don’t wake up the entire house
  • Allow decent pressure in the en-suite when I put in a new shower next year (this is a factor as the existing pump wouldn’t do this and no one seems to have a good word to about shower pumps)
  • Freed up cupboard in bedroom would be very useful
  • Faster bath fill times
I have had 2 quotes for a 210 litre installation. One at £1,400, and one at £2,300. The plumber at £2,300 recommended that he also pressurises the central heating system which I am assuming is responsible for the extra cost.
  1. Is the pressurised a good idea? Presumably he thinks it is as he said my boiler won’t need to work as hard. When I put this to the other plumber, he said he wouldn’t recommend it as we don’t know the integrity of the pipes and there would be a greater chance of leaks.
  2. I’m a bit limited by loft space as I have a low apex. Is 210 litres enough? There will be two bathrooms and eventually 2-3 children.
  3. Any better ideas than having this solution fitted?
  4. The £1400 plumber measured my flow rate and the £2300 one did not but did run a tap upstairs. The flow rate was 15l per minute. He says that this is sufficient. I see a lot of stuff out there saying a minimum of 20l. Should I be concerned by this? I don't want poor showers after spending this money!
Sorry for the long post but thought best to include as much information as possible. Hope someone can help. Thanks!
 
Adam Fell said:
Is the pressurised a good idea? Presumably he thinks it is as he said my boiler won’t need to work as hard. When I put this to the other plumber, he said he wouldn’t recommend it as we don’t know the integrity of the pipes and there would be a greater chance of leaks.
Click to expand...
1st plumber is wrong (makes no difference to 'how hard' the boiler works), 2nd is correct - leaks are possible.

210L should be enough, bear in mind that you don't use all of the hot water and then reheat - heating the cylinder can and usually should be done while it's being used.

Limited choices - it's either a pumped solution (much better pumps are available than the one you have including those which would do the whole house) or an unvented cylinder.

15l/minute isn't that good, and for 2 bathrooms used simultaneously is next to useless - in theory you could get 2 showers of 7.5 l/min, in reality a bit less, and if someone also uses the kitchen tap or flushes a toilet, even less than that.

How and where was the flow measured? Was the pressure measured as well?
 
Thanks for the reply. I don't know if the pressure was measured. He used a device for a few seconds to measure it.

I thought that the advantage of an unvented cylinder would mean I would get mains pressure from all showers and taps? i.e. In my case 2 showers running up to 15l per minute?
 
I might be making an assumption here but you mention that "but did run a tap upstairs. The flow rate was 15l per minute"

Does that mean he checked an upstairs tap? Almost certainly this would be connected to a feed tank above it, so the true measure is at a cold mains outlet like the kitchen sink or a hose tap. Easy to measure - a 5 litre bucket and stopwatch.
 
Sorry - the flow rate was measured from the kitchen by the £1,400 quote plumber. The other plumber just turned on the tap from the bathroom upstairs.
 
15l flow rate is a bit too low for an unvented imo. As said, you will certainly not get adequate performance from 2 showers and maybe not even 1 if someone turns a tap on.

My current properly as an unvented cylinder with 20l flow and 2bar dynamic pressure, and it's borderline suitable.

You could look into upgrading your incoming mains pipe and/or installing an Accumulator depending on other circumstances.

Otherwise, a pumped system is probably better.
 
Adam Fell said:
I thought that the advantage of an unvented cylinder would mean I would get mains pressure from all showers and taps?
Click to expand...
Yes - but if the mains is poor, so will what you get from each outlet.
An unvented cylinder can only supply water at the rate it is put in - it's not a magic solution for poor flow or low pressure.

Adam Fell said:
i.e. In my case 2 showers running up to 15l per minute?
Click to expand...
One shower theoretically at 15l per minute. Using two means half the flow for each, three is a third of the flow and so on.
Most people would consider a 7 litre/minute shower to be feeble in the extreme.
 
Ok thank you... So if I was going to do it I might expect to have an electric shower put in the en-suite then. I told both the plumbers that I wanted it to do 2 showers but they didn't say anything which is annoying.
 
If I had an electric shower fitted in the en-suite would either shower be affected by each other?
 
And is there any benefit of me going for the pressurised central heating system? Seems to me that decision is independent of getting an unvented cylinder.
 
Adam Fell said:
So if I was going to do it I might expect to have an electric shower put in the en-suite then.
Click to expand...
No, because it connects to the same water supply to your house, so when that's on, once again the incoming flow is shared between whatever is in use.

Adam Fell said:
And is there any benefit of me going for the pressurised central heating system?
Click to expand...
No, and there are possible problems that could result from it.
One other consideration is that some boilers can't be used on a sealed / pressurised system, others can only be used with that. Some can be used on either.

You really need to establish what the actual flow rate and pressure is. Just turning a tap on is not particularly useful, it should be done with an open pipe as taps will restrict the flow, as can flexible hoses used to connect to them, isolators which are not full bore (most are not), main stopcock partially closed, etc.

Once that information is known, you can decide on what system would be suitable. No point in installing something only to find it doesn't work properly due to an inadequate water supply.
 
Adam Fell said:
If I had an electric shower fitted in the en-suite would either shower be affected by each other?
Click to expand...

You can’t get more out of less (apart from more aggro out of a less than perfect installation :whistle:).

If you have “15lpm” coming into your property, that is all you have and will be subdivided by each outlet/demand that is imposed upon it.

You need to calculate your own flow-rate, within your boundary using a container of known volume and a stopwatch, you can then do some simple math to calculate what litres-per-minute you are getting.
This needs to be done from the least restricted outlet that you can access - typically an outside tap or washing machine valve... kitchen taps are often restricted by flexi-hoses and internal gubbins to shape spray pattern etc.

Once this figure has been obtained you can then ask your water supplier to carry out a similar test at their stopcock, to your property. This will show if it is worth upgrading your main from the street to your internal stopcock.
 
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