Can I move to an unvented hot water system ?

wwwebber · 8 Jan 2018

Hi, been pondering this for a while and need some help please.

We are currently running a pathetic electric shower and want to replace it with a monsoon type mixer running directly from the hot water tank. We also want to install a similar shower in the the en-suite.

We've been told that as an absolute minimum we'd need to install a new pump to get hot water to the showers with enough pressure. Also, we've been told that if we want to run two such showers then a larger cylinder might be required otherwise we'd run out of hot water quite quickly. All good so far.

So, as we'll probably need to replace to the cylinder anyway I want to look into the possibility of moving to an unvented system so that we can remove the header tank in the loft room. A few questions in this regard :-

Our cold water feed into the house is only 15mm and comes in at about 14 litres per min. Is this suitable for an unvented system ?
Can an unvented system supply enough hot water to the two showers without the need for a dedicated pump ? or will this still be needed ?

Thank you for your time.

Gasguru · 8 Jan 2018

14 litres/min is really too low but you should start by measuring the Static pressure ie. the water pressure with no taps open. We can then tell whether there is likely to be an issue with the service pipe work/stopcocks/taps etc.

A 15mm pipe is not necessary an issue providing the pressure is sufficient...we have 30 litres/min on an old 1/2 inch copper supply but we get 5 bar static pressure...obviously dropping with flow.

wwwebber · 9 Jan 2018

Gasguru said:
14 litres/min is really too low but you should start by measuring the Static pressure ie. the water pressure with no taps open. We can then tell whether there is likely to be an issue with the service pipe work/stopcocks/taps etc.

A 15mm pipe is not necessary an issue providing the pressure is sufficient...we have 30 litres/min on an old 1/2 inch copper supply but we get 5 bar static pressure...obviously dropping with flow.

Cheers. How do I measure static pressure ? or is this outside the domain of the DIYer ?

wwwebber · 9 Jan 2018

Scratch that - found a pressure gauge at Screwfix. I'll report back.

wwwebber · 9 Jan 2018

Ok, I have 3 to 3.5 bar of static pressure. Any good ?

Gasguru · 10 Jan 2018

I'd have thought with that static pressure you should be able to get far more than your 14 litres/min...check the boundary and internal stopcocks are fully open. I suspect some restriction somewhere.

You really need to have the gauge connected whilst progressively drawing off water to see what sort of flowrate you have at say 1 bar.

I really don't see the point of monsoon type shower heads flowing at 20 litres/min or more...complete waste of energy.
A shower head with an 8 to 10 litre/min flow limiter is more than adequate. Electric showers are often as low as 5 litres/min.

ianmcd · 10 Jan 2018

Sorry but static pressure means nothing to anyone except the supplier of your water.

wwwebber · 10 Jan 2018

ianmcd said:
Sorry but static pressure means nothing to anyone except the supplier of your water.

I was asked for static water pressure and I provided it. Care to suggest what is actually a meaningful measure here ?

ianmcd · 10 Jan 2018

Static pressure is only what is in the mains when nothing is being used, this means nothing to anyone other than the supplier, your concerns are the flow rate and working pressure, more flow rate than anything but useful if you know the working pressure when specifying which shower and cylinder to buy.

Gasguru · 10 Jan 2018

FFS stop confusing the poster. I'd pretty much stopped coming onto the plumbing section due to idiots butting in...

Of course it's useful to know the static pressure...if he's only got a bar out in the street then we can call it a day. The fact he's got over 3 bar means an unvented might still be an option....even on a 15mm service.

Given the posters got little knowledge of plumbing let's try and keep it simple to start with, rather that throwing in pointless postings.

AdvanceHelpline · 11 Jan 2018

Here's what you do. Pick a tap connected to the cold mains (kitchen sink) and turn it on. That's approximately what an unvented hot out will give you. Now turn on a second mains tap (hose tap?) and see what happens to the flow. That's what happens when two hot outlets are on. It will give a fair approximation.

Gasguru · 11 Jan 2018

Really, no further investigations...why has he got 3 bar+ and such a low flowrate?

Time I shoved off back to the CC where there's a little more competence. Hope your not a pro Advance.

Doggit · 11 Jan 2018

Aww, don't do that Gasguru; some of take actually take in the pearls of wisdom.

Okay wwwebber, in essence, if you want to for 2 showers, and are prepared to put in an unvented cylinder, are you also prepared to install a new water pipe. How far from the mains main stop cock in the street are you - it's not difficult to do, but no point doing one, and not the other.

But what sort of flow rate are you considering from a "monsoon" type shower. I've got a drench type head running of a 27Kw combi boiler, and it's fine,and I've been in hotels where I wouldn't want to pay the water bills. Plus of course, the faster the shower, the less time you can be in there before the tank needs to recover.

wwwebber · 12 Jan 2018

Doggit said:
Aww, don't do that Gasguru; some of take actually take in the pearls of wisdom.

Okay wwwebber, in essence, if you want to for 2 showers, and are prepared to put in an unvented cylinder, are you also prepared to install a new water pipe. How far from the mains main stop cock in the street are you - it's not difficult to do, but no point doing one, and not the other.

But what sort of flow rate are you considering from a "monsoon" type shower. I've got a drench type head running of a 27Kw combi boiler, and it's fine,and I've been in hotels where I wouldn't want to pay the water bills. Plus of course, the faster the shower, the less time you can be in there before the tank needs to recover.

Just had a new kitchen installed so putting in a new water pipe is not gonna work as no doubt it'll also need to go all the way up to the cylinder so will be very destructive. OK, a monsoon is probably not the right description for what we want - but we do want a decent soaker at the very least which is what we had off our combi at our last house which was also fed by a 15mm pipe lol. Running two showers is a "nice to have" but the most important thing is that we get a decent flow on at least one mixer. If we have to be careful not to run two showers then so be it.

This is similar to what we had at our last house and it worked very well :-

https://www.victorianplumbing.co.uk/adora-fusion-250mm-round-fixed-head-wall-mounted-arm-mbfuwf25

Doggit · 12 Jan 2018

Yup, it's a drench type shower head; reasonable choice. Can you change the pipework from the kitchen to the megaflow to 22mm, and get a 25mm MDPE pipe into the kitchen. It'd be a shame to get a great new system in, and then find you need a rota system to use the showers.

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Can I move to an unvented hot water system ?

Doggit

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