Running hep2O in insulation below screed?

[JohnMo]

37 minutes ago, G and J said:

Earlier today I drew up a list of the feeds I will be serving from hot and cold manifolds placed (as per current thinking

That's why mine is simple - one hot one cold to each wet room only. KISS wins the day

[G and J]

2 minutes ago, JohnMo said:

That's why mine is simple - one hot one cold to each wet room only. KISS wins the day

I’m quite sold on the radial idea, absolutely no buried joints.  Plus 10mm hot water feeds for each basin to deliver warm water PDQ.

[JohnMo]

3 minutes ago, G and J said:

I’m quite sold on the radial idea, absolutely no buried joints.  Plus 10mm hot water feeds for each basin to deliver warm water PDQ.

Get those big manifolds and stop complaining 😁

[G and J]

4 minutes ago, JohnMo said:

Get those big manifolds and stop complaining 😁

Everyone needs a hobby…

[JohnMo]

54 minutes ago, G and J said:

hot manifolds placed (as per current thinking) above the UVC in the utility room

Serious note, the manifold directly above the UVC may lead to a thermosyphon wicking away the hot water. You need to make a heat trap first. Once you have the heat trap you can do what you wish with the piping and have manifold above the UVC without risk of the thermosyphon occurring. 

 

[G and J]

50 minutes ago, JohnMo said:

Serious note, the manifold directly above the UVC may lead to a thermosyphon wicking away the hot water. You need to make a heat trap first. Once you have the heat trap you can do what you wish with the piping and have manifold above the UVC without risk of the thermosyphon occurring. 

 

In my naivety when I plumbed here in ‘91 I put a nice fat pipe straight from the top of the hot water cylinder (that’s what we called ‘em in the old days) going up into the loft to be the vent pipe bent over the tank.  Perfect heat dissipation device.  Sigh. 
 

How many litres of heating oil has that cost in the last 34 years I wonder.  
 

I’m thinking an insulated copper pipe up from the UVC outlet, then three bends, then me manifolds starting with the 10mm ones for the sinks/basins.  I’ll draw it out beautifully, then the execution will look like spaghetti. But with the cupboard door shut it will look fine. 
 

Does the balancing valve go before or after the UVC?

[JohnMo]

20 minutes ago, G and J said:

balancing valve

It's part of the combi valve that goes on the cold water feed into the cylinder.

[G and J]

2 hours ago, JohnMo said:

It's part of the combi valve that goes on the cold water feed into the cylinder.

So I don’t have to allow room between UVC and anti thermal loopy thing and manifolds then.  Good news. Thank you. 

[Nickfromwales]

22 hours ago, JohnMo said:

Serious note, the manifold directly above the UVC may lead to a thermosyphon wicking away the hot water. You need to make a heat trap first. Once you have the heat trap you can do what you wish with the piping and have manifold above the UVC without risk of the thermosyphon occurring. 

Not that I ever throw any spanner’s into any works……

 

18 hours ago, G and J said:

So I don’t have to allow room between UVC and anti thermal loopy thing and manifolds then.  Good news. Thank you. 

……actually I’d think this through before making a bad choice .

 

In that pic you’ll see I’ve provoked (intentionally) this exact thing to happen, as with the last setup I did, and it’s how I will plumb the next, and the next.

 

Short lived will be your cunning and planned celebrations of the joys of foreseeing this ‘terrible loss of heat’, and the use of 10mm pipe to get your DHW swifter than a swift flying during a hurricane, as it’ll go tits up the second you do your anti-gravity / convention loop.

 

All the wasted (and useless) water volume held in that plus the fact it’ll either be 28 or 22mm pipe, will instantly negate all this as you’ll prob have longer to wait than if you’d run the feeds in 15mm.

 

By the time you get the dead leg out of the primary larger bore pipework and then premium (useful temp) DHW out of the average outlet you’ll be sadder than Mr.Bean when he lost his teddy bear as you will then realise it was the wrong choice to set it up this way.

 

The ACTUAL annual costs (perceived savings of stopping heat wicking up the pipework) would need to include the wasted cold mains water that you then draw off as useless dead leg, then you’re very much into the price of a decent meal for 2, in ACTUAL reality. 

 

Then factor in that this primary DHW pipework will be well insulated plus the sobering reality that this aforementioned ‘runaway convection’ just won’t happen, (as you refer to with the open pipe / vent of yesteryear (which is entirely misleading and utterly irrelevant here btw!)), and then you place a cherry on top.

 

The cherry is, that with the large bore primary pipework already preheated by (local) heat wicking up it from the UVC, this then cancels out the delays caused by lengthening the pipework between the UVC and the hot manifold; viola!
 

The result you want from this is for the pipework from the UVC to the hot manifold, AND the hot manifold itself to be warm / hot as the default; insulated to stop latent losses as best as is practicable. 
 

THEN, my dear Watson, your plan of using the 10mm feeds will be one of genius, but more importantly will then actually bear some fruit.

 

Convection (runaway) can’t happened here as there needs to be an unobstructed path from hot > cold to create a convection loop, as your taps / outlets will be closed, the case for this is closed.

 

Use this ‘problem’ to your advantage squire .

Edited April 28 by Nickfromwales
Typo

[Nickfromwales]

13 hours ago, G and J said:

So I don’t have to allow room between UVC and anti thermal loopy thing and manifolds then.  Good news. Thank you. 

Anti convection loop would have to go between the UVC and the manifold. 
 

But it doesn’t matter because you’re not going to install one……..😉🤝

[G and J]

45 minutes ago, Nickfromwales said:

Not that I ever throw any spanner’s into any works……

 

……actually I’d think this through before making a bad choice .

 

In that pic you’ll see I’ve provoked (intentionally) this exact thing to happen, as with the last setup I did, and it’s how I will plumb the next, and the next.

 

Short lived will be your cunning and planned celebrations of the joys of foreseeing this ‘terrible loss of heat’, and the use of 10mm pipe to get your DHW swifter than a swift flying during a hurricane, as it’ll go tits up the second you do your anti-gravity / convention loop.

 

All the wasted (and useless) water volume held in that plus the fact it’ll either be 28 or 22mm pipe, will instantly negate all this as you’ll prob have longer to wait than if you’d run the feeds in 15mm.

 

By the time you get the dead leg out of the primary larger bore pipework and then premium (useful temp) DHW out of the average outlet you’ll be sadder than Mr.Bean when he lost his teddy bear as you will then realise it was the wrong choice to set it up this way.

 

The ACTUAL annual costs (perceived savings of stopping heat wicking up the pipework) would need to include the wasted cold mains water that you then draw off as useless dead leg, then you’re very much into the price of a decent meal for 2, in ACTUAL reality. 

 

Then factor in that this primary DHW pipework will be well insulated plus the sobering reality that this aforementioned ‘runaway convection’ just won’t happen, (as you refer to with the open pipe / vent of yesteryear (which is entirely misleading and utterly irrelevant here btw!)), and then you place a cherry on top.

 

The cherry is, that with the large bore primary pipework already preheated by (local) heat wicking up it from the UVC, this then cancels out the delays caused by lengthening the pipework between the UVC and the hot manifold; viola!
 

The result you want from this is for the pipework from the UVC to the hot manifold, AND the hot manifold itself to be warm / hot as the default; insulated to stop latent losses as best as is practicable. 
 

THEN, my dear Watson, your plan of using the 10mm feeds will be one of genius, but more importantly will then actually bear some fruit.

 

Convection (runaway) can’t happened here as there needs to be an untreated path from hot > cold to create a convection loop, as your taps / outlets will be closed, the case for this is closed.

 

Use this ‘problem’ to your advantage squire .

I’m Wally the warm water molecule.  And I’m going to describe my morning commute. 
 

I spent the night getting warmer and warmer in the big space, we call it the coil cavern. It’s nice swimming round the coils, as the thermals are a bit of a funfair ride.  
 

Someone turned a tap on and I happened to be near the hole in the ceiling, so I got sucked up.  The first bit of metal tube was vertical but still lovely and warm. And we moved at a good pace so it was fun. 
 

We got quite roughly jostled at a sharp 90 degree bend, I got an elbow in the eye.  Not happy. This metal tube was horizontal and still as warm. 
 

Then it got odd.  
 

I got wrenched downwards into a tiny plastic tube.  The speed!  Wow. But I must have been near the front as I got progressively cooler as the tube went on.  Then by the time I hit and fell out of the metal sluice gate thing I could feel a migraine coming on. 
 

Later, as I serenely swam round with some cold water molecules and detergent strings in the big, calm, luke warm pool, I was told that my hot water team got there really quickly and were still nice and hot.  
 

I know that in a while the chrome rimmed hell hole will open, sucking us all into the underworld.  And who knows how long before I’ll be reincarnated back to the warm coil cavern. 
 

But for now I’m enjoying swimming round with the suds.  All I have to do is avoid that big pink thing in the middle. 
 

(I thought I should look at this from every angle, and the lesson? Maybe I should put bends in rather than elbows to make the water journey more comfortable.  
 

Being serious I take your point @Nickfromwales re cold water volume in a heat trap.  We’ve just been discussing it and as J has pointed out, the UVC is in a drying cupboard, so the heat isn’t wasted.  
 

All those litres of oil weren’t entirely wasted, we always had a nice warm airing cupboard - and being 60s kids that felt right.  

[Nickfromwales]

11 minutes ago, G and J said:

I’m Wally the warm water molecule.  And I’m going to describe my morning commute. 
 

I spent the night getting warmer and warmer in the big space, we call it the coil cavern. It’s nice swimming round the coils, as the thermals are a bit of a funfair ride.  
 

Someone turned a tap on and I happened to be near the hole in the ceiling, so I got sucked up.  The first bit of metal tube was vertical but still lovely and warm. And we moved at a good pace so it was fun. 
 

We got quite roughly jostled at a sharp 90 degree bend, I got an elbow in the eye.  Not happy. This metal tube was horizontal and still as warm. 
 

Then it got odd.  
 

I got wrenched downwards into a tiny plastic tube.  The speed!  Wow. But I must have been near the front as I got progressively cooler as the tube went on.  Then by the time I hit and fell out of the metal sluice gate thing I could feel a migraine coming on. 
 

Later, as I serenely swam round with some cold water molecules and detergent strings in the big, calm, luke warm pool, I was told that my hot water team got there really quickly and were still nice and hot.  
 

I know that in a while the chrome rimmed hell hole will open, sucking us all into the underworld.  And who knows how long before I’ll be reincarnated back to the warm coil cavern. 
 

But for now I’m enjoying swimming round with the suds.  All I have to do is avoid that big pink thing in the middle. 
 

(I thought I should look at this from every angle, and the lesson? Maybe I should put bends in rather than elbows to make the water journey more comfortable.  
 

Being serious I take your point @Nickfromwales re cold water volume in a heat trap.  We’ve just been discussing it and as J has pointed out, the UVC is in a drying cupboard, so the heat isn’t wasted.  
 

All those litres of oil weren’t entirely wasted, we always had a nice warm airing cupboard - and being 60s kids that felt right.  

I’ll read that to the kids before bedtime. They’ll be confused but fascinated lol.

 

12 minutes ago, G and J said:

Being serious I take your point @Nickfromwales re cold water volume in a heat trap

👌

 

1 hour ago, Nickfromwales said:

But it doesn’t matter because you’re not going to install one……..😉🤝

👆👉💪😊

[G and J]

2 hours ago, Nickfromwales said:

 

 

4 hours ago, Nickfromwales said:

But it doesn’t matter because you’re not going to install one……..😉🤝

👆👉💪😊

Can you really be sure of that?

[Nickfromwales]

8 minutes ago, G and J said:

Can you really be sure of that?

Mine is the truth and the light…..

 

 

 

etc etc 

 

 

 

But some horses do refuse to drink lol. 🤷‍♂️🙃

[MikeSharp01]

On 23/04/2025 at 09:40, Nickfromwales said:

 

Can I ask when is it right to and not to lollypop the manifold as it you have it on the 7 way but not on the 2 and 3 way when would a 5 way need it or not or are there other factors?

[G and J]

8 hours ago, MikeSharp01 said:

Can I ask when is it right to and not to lollypop the manifold as it you have it on the 7 way but not on the 2 and 3 way when would a 5 way need it or not or are there other factors?

I’m assuming that ‘lollypopping’ is to ensure good flow even if, say, two showers were in use at the same time, so for circuits where flow rate rather than hot water arrival speed is of interest.  
 

In my ever evolving mental plumbing layout (mental being the right word, sigh) I have a single ended connection from and as close as possible to the top of the UVC direct to a small manifold that serves just the sink/basin taps.  
 

Then I’ll have a sculptural Henry Moore style loopy manifold for the rest.  I think I’ll entitle it “warm in the shower despite his plumbing”.

[Nickfromwales]

14 hours ago, MikeSharp01 said:

Can I ask when is it right to and not to lollypop the manifold as it you have it on the 7 way but not on the 2 and 3 way

Far left (non lollypopped?) is a 22mm feed to a 3/4” 2-port manifold, with 2x 15mm outlets, ergo the sum of the output cannot ever exceed the sum of the input, or words to that effect.
 

When you get to the 7-way then the maths change; if you squint a bit you’ll see this gets fed from 28mm vs the 22mm used for the 2 and 3 port manifolds. Just some simple plumbers maths, nothing more.

 

The 3-port is the hot return with 10mm pipes, so just a crawl there.

 

You’ll notice that there’s 2x TMV’s immediately off the 28mm hot outlet of the UVC. Left one (22mm) feeds the kitchen and utility sinks @50°C, and the right one (28mm) feeds all sinks, bath, showers at 45°C. As this is Hep2o and there have been ‘issues’ with using it for hot return, I follow their guidelines and a) time the HRC so it’s not ‘on constant’, and b) temper the water in that loop so it’s not ever at the terminal temp of the UVC; that can be north of 70°C if solar PV excess or cheap rate electricity is fed into the immersion, plus the 45°C flow temp of the HRC means much lower losses too. 👌. 

 

14 hours ago, MikeSharp01 said:

when would a 5 way need it or not

Again, it’s down to dynamics of the particular site, but at 5 ports (and the assumption that some were basins) I’d have said it’s fine on 1x 22mm feed from one side.

 

Bath and shower outlets seem to feed at roughly the same rate, as EU compliant and low water consumption outlets are commonplace nowadays, so no need to worry about huge flow rates to a very big bath for eg (unless you actually have one, and then the conversation would change) . Then, and then alone, I’d say have that closest to the feed end, but prob arguing over pocket change there tbh as the manifolds are 3/4” bore which is quite decent.

 

14 hours ago, MikeSharp01 said:

or are there other factors?

Oh, if only you hadn’t said that bit, I could have stuck to a simple reply lol.  😌

 

So, for ”The science bit”…..(please manage your expectations here). 

 

Dynamic flow rates at the incoming cold mains will affect how I ultimately ’plumb things’, but I also respect my clients enough to give them a minimum expected level of GAF, so, then the ‘problem’ and the solution become more relevant (and apparent, hence what you’ve seen and the question it has provoked); at which point I will assume a responsibility to provide a solution that is engineered to yield the best possible results, for the given circumstances, as the minimum standard. 

 

For the 7-port manifold, 28mm flow is then divided at a 28mm tee (22x22x28c) into 2x 22mm feeds to each end of the 7-way (port) manifold so ‘theoretically’ 3.5 ports each get fed from 22mm feeds, a-la an electrical socket outlet in a ring main.

 

”Couldn’t I just feed one end of that manifold with a 28x3/4 feed?”, you may ask.
 

Yes you could, in reality, more-so when the cold mains is much better for eg, but when the house is occupied, all rooms in use, bathrooms a-blazing’, the ‘solution’ comes into play because the setups I design / deliver can cope under duress, admirably, with one hand tied behind its back.
 

Would someone get upset if 3 showers didn’t work simultaneously, and if they did, albeit poorly, would they accept that they could only be hot for <10 minutes each before going cool then cold? Yes, they’d be quite upset that the brand new 6 or 7-figure home they’d just spent their life savings on failed to perform when it was occasionally at capacity. It would be a bit of a ballache at the least, borderline embarrassing at the worst, have to schedule your guests bathing methinks, but there are plenty of folk out there who would say that’s “fine”….I’m not one of them obvs 🙄👎. 

 

I don’t design systems and install stuff to be “OK”, there are plenty of people churning out that level of crap, and I don’t fit a 2 person setup in a 5 bed / 3 en-suite / 1 family bathroom home; (caveat: unless I am directly told to do so and I’ve covered my arse against recourse by getting that in writing).

 

Chinese Confucius say…”you can turn a big system down, but you can’t turn a small system up, grasshopper”. 🙏
 

I install stuff to suit the size and capacity of the dwelling and I don’t deviate far from that, ever, as that services nobody’s interests well; my ethos is plumb to suit the capacity of the house and the worst case, and then nobody will ever be disappointed.
 

For the above project I also installed a 300L cold mains accumulator as the owner reported mass local development and the loss of 1bar of pressure over the last ~2 years! That’s also why all the cold mains and primary stuff is done in 28mm / 1” BSP, including the 1”/28mm large-bore flexis used to connect to the high flow water softener.

 

And so on….

 

Amen. 

[MikeSharp01]

1 hour ago, Nickfromwales said:

And so on….

 

Amen. 

Thanks Nick very comprehensive....

[Nickfromwales]

Just now, MikeSharp01 said:

Thanks Nick very comprehensive....

If I could just say a few words…… 😉🙃

[MikeSharp01]

Any chance of seeing a schematic of that little lot as when you read this whole thread it's a lot to take in.

 

 

[Nickfromwales]

1 hour ago, MikeSharp01 said:

Any chance of seeing a schematic of that little lot as when you read this whole thread it's a lot to take in.

 

 

That lot just appears in my brain, after a few cups of ☕️ and some in-house procrastinating, and then I just start cutting and soldering.

 

That pic is the result.

 

By the time someone’s done the design, I’ve usually finished the job.

 

To answer your question, erm….”no”, sorry. 😕, but to affirm, you’d not really want it as I spec & design each job uniquely (under the well known 2019 “horses for courses” act). 

[MikeSharp01]

Yes thought that might have been the case, thanks for looking

[Nickfromwales]

Prob best to add, that I don’t see much value in charging clients for designs, as most change their mind a good few times and then all that time / work is 💰 🔥.