On 21/05/2017 10:54, Terry Casey wrote:
In article ,
says...

Some background things to check. Is your mains flow rate adequate for a
combi? (you need a minimum of 15 lpm really, and more is better).

We are away at the moment but I will check it when we return in early June

Yup, time filling a bucket of known volume from your fastest tap.

Is the pressure adequate. 3 bar or better is good.

I have no way of checking this unless there is some simple method I could use

You can get a pressure testing kit from a plumbers merchant. Normally
about 10 to 15 quid. Includes a gauge and selection of adaptors to
attach it to different types of tap.

Is the water supply reliable? (if not, some stored water may be handy).
Have you though about backup water heating if the boiler were in need of
repair?

No supply problems in the year we've been there - although not all the time!

The electric shower heater should suffice for washing and the dishwasher and
washing machine would take care of most other essentials. The kettle will,
hopefully, cater for any more demand.

Yup, that's a resonable backup plan.

If looking at stored water systems, have your installers been thinking
about using a conventional gravity fed cylinder, or an unvented one?
(the latter tend to give better overall system performance if there is
adequate mains flow rate availble)

As the quote we are most interested in offers the option of a like for like
replacement instead of the combi, I was assuming that the cylinder would
remain gravity fed but will check.

You can also use a combi to heat a cylinder, but then pipe its DHW feed
to somewhere where it will be of advantage. Say feeding a shower (high
pressure without a pump), or a kitchen hot tap - e.g. save time by
filling a saucepan with pre-heated water prior to boiler etc.


--
Cheers,

John.

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On 20/05/2017 19:24, The Natural Philosopher wrote:
On 20/05/17 13:56, Phil L wrote:
The Natural Philosopher wrote:


Mate, the combi I have here currently wont even supply enough hot
water to drive ONE hot tap, bath or shower.,

All this proves is that you have low mains pressure

Compltely and utterly wrong

main pressure is about 8 bar

what i have is a combi that cant heat water fast enough and has
minuscule hott water store

So you need to turn the tap on less hard, or throttle the inlet with the
valve on the cold inlet to the boiler.

If you are expecting stored water bath fill rates from a combi, then you
are likely to be disappointed.

My combi is ten years old, never been serviced and supplies continuous
hot
(hard) water every time the tap is turned on, likewise the mixer shower,
which is powerful enough to actually hurt if it's on full.

no, it doesn't unless yu have around 50Kw rating

A small combi will do a decent shower (unless you want soaker heads or
additional body jets etc).

No water softener ever been in this house
To the OP, get a combi if you have reasonable mains pressure, if it comes
out of the tap like someone having a ****, go the other option


oh the water comes out aright. Cold

work out how big a combi needs to be to say dump 400 litres a minute of
water at 60 degrees

There will be very few households where the incoming main can supply at
that rate (or anything close to it). 40 lpm perhaps.

then work out how much more expensive that is than a small boiler with a
mains pressure hot water tank

then do the sensible thng

Which for a property with a couple of people, and one shower, may well
be fit a combi and save two grand.


--
Cheers,

John.

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On 21/05/17 11:11, ARW wrote:
On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

You don't have to stand there and watch the bath fill up!


My ex used to a pathetic flow rate, used to start the bath and leave it.

And being deaf, forget it.

Twice there was water pouring through the ceiling.



--
How fortunate for governments that the people they administer don't think.

Adolf Hitler

On 20/05/2017 20:37, Andrew wrote:
On 20/05/2017 19:44, Phil L wrote:

If all four showers are used concurrently, while someone is also
using hot water in the kitchen then there will be a problem.

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the
heat exchanger. So choose between showers running like a poor
old sod with a prostate problem or lukewarm water.

I found a 35kW combi will do a pair of showers concurrently. Not going
to do 4 obviously - but its unlikely in a domestic setting that all 4
would be in use at exactly the same time.

And while this is happening all the heating stops.
This can be a problem with an old leaky house.

That is also a problem with modern unvented cylinders as well.

Old cylinders had low heat transfer rate coils that would only absorb
say 5kW at best. That meant there was logic to using a Y plan
arrangement which allowed the boiler to run more efficiently feeding the
rads and the cylinder, rather than short cycling with just the cylinder
that could not take its full output.

A modern unvented cylinder will have a much larger coil that can take
heat at 20kW plus. That means you can direct the full output of the
boiler at it. Hence its better suited to W or S plan style control
systems (unless you have a very powerful boiler) but no heating while
its recharging.

(there is another reason for directing the full output of the boiler at
the cylinder, in that it then allows split temperature operation -
running much higher flow temperatures into the cylinder than you use for
the rads, gaining extra condensing efficiency on your heating)


--
Cheers,

John.

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On 20/05/2017 21:47, Harry Bloomfield wrote:
The Natural Philosopher wrote on 20/05/2017 :
work out how big a combi needs to be to say dump 400 litres a minute
of water at 60 degrees

then work out how much more expensive that is than a small boiler with
a mains pressure hot water tank

then do the sensible thng

For someone in at irregular times, where a timer cannot be set and who
doesn't mind waiting for the hot water to appear very slowly,

Combis with pre-tempered water stores, don't suffer the delay problem so
much.

they are
fine. For everyone else, who wants a bath filled rapidly, who might need
to run two taps at the same time - stored hot water.

Bath filling will be more of a challenge - when you work out the
equivalent heating rate required to match a cylinder you will often
arrive at 100kW or more, and you are not going to be able to suck that
much gas through a domestic meter!


--
Cheers,

John.

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On 20/05/2017 19:26, The Natural Philosopher wrote:
On 20/05/17 18:29, Tim Watts wrote:
On 20/05/17 17:51, Max Demian wrote:
Should be OK unless you have hand washing OCD. Combis are adequate for
small or medium flats/houses unless you have more than one bathroom.


Given you can get combis up to 35-42kW (WB) they should be adequate
for 2 bathroom properties. WB even do a floor standing combi with
insane DHW flow.

a 40kw combi costs a lot more than a 10kw system boiler with a mains
pressure tank

Vaillant ecoTec 612 £916
Vaillant unistor 120L £605

Vs

Vaillant ecoTec 838 combi £1497

Odd definition of "a lot more"...


--
Cheers,

John.

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On 21/05/2017 11:45, John Rumm wrote:
On 21/05/2017 09:41, Scott wrote:
On Sat, 20 May 2017 21:48:49 +0100, John Rumm

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

It does seem to make a big difference. Or at least if the heating is
on the water arrives more quickly.

Yup, having eco mode turned off makes it far more usable IME - with
faster hot water delivery, especially when all you want is a small
amount. Eco mode on will save some gas, but I would not expect it to
make a significant difference to consumption in most households.

The eco mode IMHO should be on a timer.




--
Adam

On 21/05/2017 12:01, The Natural Philosopher wrote:
On 21/05/17 11:11, ARW wrote:
On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

You don't have to stand there and watch the bath fill up!


My ex used to a pathetic flow rate, used to start the bath and leave it.

And being deaf, forget it.

Twice there was water pouring through the ceiling.




Blonde?

--
Adam

In article ,
John Rumm wrote:
A modern unvented cylinder will have a much larger coil that can take
heat at 20kW plus. That means you can direct the full output of the
boiler at it. Hence its better suited to W or S plan style control
systems (unless you have a very powerful boiler) but no heating while
its recharging.


I have what was known as a fast recovery cylinder which stores my hot
water. I dunno what the maximum transfer rate is, but it is enough to
provide a warm shower constantly. Ie, starting out from cold, as I
discovered on coming back from holiday some years back, and wanted a
shower before going out again - I was willing to risk a cold one. ;-)

--
*If one synchronized swimmer drowns, do the rest have to drown too?

Dave Plowman London SW
To e-mail, change noise into sound.

On 21/05/17 13:43, ARW wrote:
On 21/05/2017 12:01, The Natural Philosopher wrote:
On 21/05/17 11:11, ARW wrote:
On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long time
to fill a bath with hot water compared with a stored hot water system.

You don't have to stand there and watch the bath fill up!


My ex used to a pathetic flow rate, used to start the bath and leave it.

And being deaf, forget it.

Twice there was water pouring through the ceiling.




Blonde?

No. mentally ill


--
The New Left are the people they warned you about.

On 21/05/2017 13:58, The Natural Philosopher wrote:
On 21/05/17 13:43, ARW wrote:
On 21/05/2017 12:01, The Natural Philosopher wrote:
On 21/05/17 11:11, ARW wrote:
On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long
time
to fill a bath with hot water compared with a stored hot water system.

You don't have to stand there and watch the bath fill up!


My ex used to a pathetic flow rate, used to start the bath and leave it.

And being deaf, forget it.

Twice there was water pouring through the ceiling.




Blonde?

No. mentally ill

After how many years living with you? ;-)


--
Cheers,

John.

/================================================== ===============\
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On 21/05/17 14:11, John Rumm wrote:
On 21/05/2017 13:58, The Natural Philosopher wrote:
On 21/05/17 13:43, ARW wrote:
On 21/05/2017 12:01, The Natural Philosopher wrote:
On 21/05/17 11:11, ARW wrote:
On 20/05/2017 21:20, Roger Mills wrote:


Firstly, do you bath or shower? Even a good combi will take a long
time
to fill a bath with hot water compared with a stored hot water
system.

You don't have to stand there and watch the bath fill up!


My ex used to a pathetic flow rate, used to start the bath and leave
it.

And being deaf, forget it.

Twice there was water pouring through the ceiling.




Blonde?

No. mentally ill

After how many years living with you? ;-)


Since childhood.

It just took a long time to realise the extent

--
"Anyone who believes that the laws of physics are mere social
conventions is invited to try transgressing those conventions from the
windows of my apartment. (I live on the twenty-first floor.) "

Alan Sokal

On 21/05/2017 13:49, Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
A modern unvented cylinder will have a much larger coil that can take
heat at 20kW plus. That means you can direct the full output of the
boiler at it. Hence its better suited to W or S plan style control
systems (unless you have a very powerful boiler) but no heating while
its recharging.


I have what was known as a fast recovery cylinder which stores my hot
water. I dunno what the maximum transfer rate is, but it is enough to
provide a warm shower constantly. Ie, starting out from cold, as I
discovered on coming back from holiday some years back, and wanted a
shower before going out again - I was willing to risk a cold one. ;-)


Mine is about 16kw nominally, but it depends on what temp you set the
flow on the boiler to and what temp you set the tank to, so its not an
easy thing to compare.
The system can keep up with the shower unless you turn on the big
overhead one which at something like 24l/minute is a bit too much.
It takes a while for you to notice as there is 120l of hot to go through
first.

In article om,
dennis@home wrote:
I have what was known as a fast recovery cylinder which stores my hot
water. I dunno what the maximum transfer rate is, but it is enough to
provide a warm shower constantly. Ie, starting out from cold, as I
discovered on coming back from holiday some years back, and wanted a
shower before going out again - I was willing to risk a cold one. ;-)


Mine is about 16kw nominally, but it depends on what temp you set the
flow on the boiler to and what temp you set the tank to, so its not an
easy thing to compare.
The system can keep up with the shower unless you turn on the big
overhead one which at something like 24l/minute is a bit too much.
It takes a while for you to notice as there is 120l of hot to go through
first.

Yes, my shower is one of the old AquaLisa low pressure high flow types -
fed with 3/4" tube. Obviously had to be set differently to work from the
boiler only.

--
*That's it! I‘m calling grandma!

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 20 May 2017 20:37:20 +0100, Andrew wrote:

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the
heat exchanger.

I think that the heat is still transferred, it just has to heat more
water in a given time, so the temp rise is less. Wherever you
learned the 'laws of physics' you should ask for your money back.

On Sat, 20 May 2017 21:20:43 +0100, Roger Mills wrote:

I've stayed with friends and relatives who have a combi in a
normal household, the hot water supply has always been dire!

Well there's no substitute for horsepower as they say. WB supply
nice 40kW machines that should be enough for any medium house.

Roger Mills wrote:

I've stayed with friends and relatives who have a combi

IRTA "I've stayed friends with relatives who have a combi" and thought
boiler choice is hardly a falling-out issue :-)

On 21/05/2017 20:47, Andy Burns wrote:
Roger Mills wrote:

I've stayed with friends and relatives who have a combi

IRTA "I've stayed friends with relatives who have a combi" and thought
boiler choice is hardly a falling-out issue :-)


LOL!
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 20/05/17 21:48, John Rumm wrote:
On 20/05/2017 18:38, Scott wrote:
On Sat, 20 May 2017 13:35:45 +0100, Terry Casey
wrote:

[snip]

I installed a combi boiler (Worcester Bosch) last year and I am a bit
disappointed with it.

24kW by any chance?

(makes for dismal bath filling - but will do a "twice as good as the
best electric" shower)

The water takes a while to heat up when using Eco mode. I mostly run
without Eco mode (pre-heat is capable of being programmed) so I assume
I am using extra energy to save water.

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

I found the pre-heat function useless, so prefer 'eco mode' anyway.
Without pre-heat (eco mode): turn on tab, wait for cool water to clear
dead leg, wait a bit longer for water to heat. Turn off tap, turn it on
to top up a while later; warm water in dead leg, then shot of too-hot
water that has been sitting in boiler, then cold as fresh water enters
the boiler before it has fired, wait for water to reach full tempreture.

With pre-heat there is always that slug of overheated water sitting in
the boiler.



--
djc

(–€Ì¿Ä¹Ì¯–€Ì¿ Ì¿)
No low-hanging fruit, just a lot of small berries up a tall tree.

My son has a combi in his flat.

When you turn the tap on it takes an _age_ to get hot water - the boiler
has to heat up first, then hot water starts running down the pipe, then
you get hot. But not very - looks like peak power on the boiler won't
feed the kitchen tap on full. Likely a fault.

And you'll need a pretty powerful one to get bath flow rates out of a
combi. Showers are good though.

We have a tank.

When our boiler goes wrong we'll put the immersion heater on to have a
hot bath or shower. There can be no immersion in a combi.

Our shower is fine - gravity fed, and downstairs. Upstairs we'd need a
pump. And we can run a bath full as fast as the tap will go.

Andy

On 5/20/2017 4:54 PM, Terry Casey wrote:
In article ,
says...

As you have probably surmised, the anti-combi guy is probably a bit of a
bull****ter, but what he says about hot water flow rates is reasonable.


As far as cold water pressure goes, there is good pressure from the kitchen
cold tap and we also have an instant electric water heater for the shower.

I have noticed that if the washing machine or dishwasher is running while I'm
having a shower with the hot water temperature nice and high, as the demand
from the kitchen appliance turns on, although I'm not aware of a pressure
drop, the temperature can suddenly nudge up from comfortably hot to
uncomfortably hot.

However, the anti-combi guy seemed to be implying that the hot water flow
from the combi would be restricted to maintain the temperature if demand
increased but I find that a bit difficult to swallow. In any case, his quote
was considerably higher than the first one, higher even than the combi quote,
so we definitely wouldn't be using him, whatever we decide. He did, however,
sow sufficient seeds of doubt to get us querying the whole combi set-up ...

One of the problems with the combi which hasn't been touched on is the
DHW heat exchanger, which is normally physically quite small to keep the
boiler size down. In case you are not familiar with how they work, the
water which goes around the radiators is heated by passing through a
number of tubes just above the gas burners. When you ask for domestic
hot water, a valve operates so that the hot water goes through the DHW
heat exchanger instead. Your hot water comes from the rising main and
goes through the other side of this heat exchanger so that it is heated
up by the "closed circuit" water. It then goes off to the bath, or
whatever. If you have hard water and no softener, you can get lime scale
on the secondary side of the heat exchanger which can affect both the
flow and the heat transfer. Also, if you don't have enough inhibitor in
the radiators, the "black sludge" which you sometimes get out of
radiators can block the primary side of the heat exchanger.

With a separate hot water cylinder, the coil in the cylinder is much
fatter, and unlikely to block with "sludge". Over time, you may get
limescale buildup on the fresh water side, but IME this is generally
much less of a problem than combi heat exchanger blocking.



I guess a "system" installation with a separate hot cylinder is going to
be a bit more expensive.


We already have a cylinder which is heated by the boiler or an immersion
heater if the CH is turned off.

If you are happy with your existing cylinder, then a "system" boiler
should be no more expensive than a combi, in fact it could be cheaper.


How old is the bungalow, and what's the insulation and draft-proofing
like? Semi or detached? There are calculators on-line to help estimate
your heating requirements which could vary by a factor of 2. Or if you
are on an estate, ask your neighbours what boilers they have, and
whether they are adequate.

Detached, although the gap between the side wall and an adjacent garage has
been roofed over and turned into two narrow storage areas, one with access
from the front and one from the back. 1961. There is 6" of insulation in the
loft or possibly 8". Adam will know because he fills the bath with the stuff
every time he goes up there!

Draft proofing is good although the aluminium framed double glazing leaves a
lot to be desired as there is obviously no thermal barrier between inside and
out. That is next on the agenda for replacement.

Whether there is any cavity wall insulation, we don't know. There are no
obvious signs of anything being done


I'd still suggest you try to estimate how much heating power you need,
either by talking to neighbours (if you have any) or by using one of the
calculators. That gives you a chance to decide whether quotes are for
the right sized boiler.

Going for a bigger boiler is obviously slightly more expensive, also the
running cost per unit of heat may be marginally higher. If you have some
secondary source of heating (say, a wood burner) that you can power up
in very cold weather you might decide to go with a slightly smaller
boiler. FWIW, although I have a big woodburner, on my last boiler
replacement I went for the biggest which would fit in my space and this
copes pretty well even in extended cold spells.

On 21/05/17 22:00, Vir Campestris wrote:
My son has a combi in his flat.

When you turn the tap on it takes an _age_ to get hot water - the boiler
has to heat up first,

Many WBs have a preheat mode which keeps everything upto the plate
exchanger hot.

then hot water starts running down the pipe, then
you get hot. But not very - looks like peak power on the boiler won't
feed the kitchen tap on full. Likely a fault.

And you'll need a pretty powerful one to get bath flow rates out of a
combi. Showers are good though.

We have a tank.

When our boiler goes wrong we'll put the immersion heater on to have a
hot bath or shower. There can be no immersion in a combi.

Thought of that - I'll keep my inline heater with valving to isolate the
boiler and enable the heater. It's 10kW but we've run off that for some
time now. Fills a bath in 20-30 minutes (summer vs winter). Needs a
little forethought, but quite workable.


Our shower is fine - gravity fed, and downstairs. Upstairs we'd need a
pump. And we can run a bath full as fast as the tap will go.

Andy

On Sun, 21 May 2017 19:38:25 +0100
mechanic wrote:

On Sat, 20 May 2017 20:37:20 +0100, Andrew wrote:

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the
heat exchanger.

I think that the heat is still transferred, it just has to heat more
water in a given time, so the temp rise is less. Wherever you
learned the 'laws of physics' you should ask for your money back.

In fact, the faster you move cold water through the combi, the MORE
heat will be transferred, as there is always cold water coming along to
take away the heat. But with a greater volume of water, the temperature
rise is lower.

--
Davey.

On 20/05/2017 13:35, Terry Casey wrote:
I note it says in the wiki that: "I need a new one, what should I get!" comes
up in some form almost every day on uk.d-i-y, but couldn't find enough
information to clench the deal, one way or the other.


We changed from storage tanks to instant combi at our least house.
Never again.
Despite water pressure being good the supply of hot water was never as
good. Then the mains in the road burst cutting off our supply for 36 hours!

How we wished we still had that big tank of water in the loft!

Mike

On Sun, 21 May 2017 21:49:43 +0100, DJC wrote:

On 20/05/17 21:48, John Rumm wrote:
On 20/05/2017 18:38, Scott wrote:
On Sat, 20 May 2017 13:35:45 +0100, Terry Casey
wrote:

[snip]

I installed a combi boiler (Worcester Bosch) last year and I am a bit
disappointed with it.

24kW by any chance?

(makes for dismal bath filling - but will do a "twice as good as the
best electric" shower)

The water takes a while to heat up when using Eco mode. I mostly run
without Eco mode (pre-heat is capable of being programmed) so I assume
I am using extra energy to save water.

Not much value in ECO mode really - it only fires fairly infrequently to
temper its small store of hot water.

I found the pre-heat function useless, so prefer 'eco mode' anyway.
Without pre-heat (eco mode): turn on tab, wait for cool water to clear
dead leg, wait a bit longer for water to heat. Turn off tap, turn it on
to top up a while later; warm water in dead leg, then shot of too-hot
water that has been sitting in boiler, then cold as fresh water enters
the boiler before it has fired, wait for water to reach full tempreture.

With pre-heat there is always that slug of overheated water sitting in
the boiler.

I was persuaded to install Combisave. It appears to cut down the
amount of water wasted but whether it saves energy I don't know. Any
ideas?

On 5/21/2017 11:43 AM, The Natural Philosopher wrote:
A system boiler of 8-15kW, plus pressurised hot water tank with the
added advantage of an immersion heater if you don't want to run the
boiler, is around £1200 in total.

A 45Kw combi to deliver the same hot water flow rate is similar, or more
costly, and is certainly bigger in the boiler room

(You can site a pressurised cylinder wherever you like)

If you have an unpressurised tank you need pumped showers.

(Interestingly, in the two new builds going up here, with no mains gas,
they are using air source heat pumps, UFH, and a pressurised tank plus
the mandatory immersion heater to bring the stored temp up to 60C to
kill the bugs. Air sourced heat pumps simply can't deliver the peak
output, and indeed the insulation level installed to allow them to even
heat the house at all is phenomenal)

To heat 15 l/min (an average single shower) from 5C to say 45C takes 42KW.

To fill a bath with water at 45C in 4 minutes is around 20l/min or 55KW.

For sure you can add a heat store to a combi at EVEN MORE EXPENSE to
give better figures than this, but that is pretty much what a DPHW
system IS.

My point is simple. Heating a house requires a constant low to medium
heat output over a long period of time. A boiler designed to do that
efficiently does not have the capability for a massive output over 4
minutes of the day when you want to fill a bath. Attempts to rectify
this with high power but modulating boilers etc simply make the boiler
more complex and costly.

The simplest solution is a heat store. Mutatis mutandis a decent sized
heatbank on a combi is no different to a system boiler with a DPHW tank
attached.

The more complex solution is a thwacking great boiler.

Prices are similar, but even then, if you install the monster combi, you
can STILL only cope with one shower or bath at a time and you cannot
open a hot tap elsewhere.


The worst solution is to enforce a pathetic rate of hot water flow on
the house-owner. Because you didn't give a **** when you built the poxy
little house you sold him.

Actually no, the worst solution is a gravity fed unpressurised tank. In
a bedroom, so no upstairs hot water pressure exists at all, and you have
to pump.

In short:

Installing a system boiler geared to the CH requirements and a DPHW tank
to provide peak flow of piping hot water gets you the optimal solution
to both problems, and is no more expensive than a small combi with a
large heat bank, or a large combi with no heat bank.


And even a large combi can't meet the same peak demands that stored hot
water can.

The only cheap option is a pathetically limited small combi with litle
or no heat bank.

Or a gravity fed cheap water tank with a system boiler.

I have experienced both. They suck, big time,.


Agree with all you say, apart from the final point; gravity fed water
tank is OK *as long as you have a shower pump, and (perhaps) one for the
other DHW*. This does add £300 to the cost: don't buy a cheap shower
pump, get a Stuart Turner.

In article ,
newshound wrote:
Agree with all you say, apart from the final point; gravity fed water
tank is OK *as long as you have a shower pump, and (perhaps) one for the
other DHW*. This does add £300 to the cost: don't buy a cheap shower
pump, get a Stuart Turner.

I have gravity hot water and no shower pump. And my shower is excellent.
But as with taps and pipework, has to be designed for lower pressure,
which most of the imported cheap stuff isn't.

--
*Oh, what a tangled website we weave when first we practice *

Dave Plowman London SW
To e-mail, change noise into sound.

newshound wrote:

don't buy a cheap shower pump, get a Stuart Turner.

I've found Salamander pretty decent, not a peep of a problem from mine
since 2009

https://www.salamanderpumps.co.uk/product/rsp75/43

On 5/22/2017 11:20 AM, Andy Burns wrote:
newshound wrote:

don't buy a cheap shower pump, get a Stuart Turner.

I've found Salamander pretty decent, not a peep of a problem from mine
since 2009

https://www.salamanderpumps.co.uk/product/rsp75/43

Just saw them when checking ST prices. They do look reputable, just
avoid Screwfix type entry level. I have seen three failures (two leaks,
one electrical iirc) in this general type.

BES have a Salamander regenerative for less than £150

https://www.bes.co.uk/ct50-twin-rege...ad-shower-pump

I guess it may be plastic rather than brass. The metal body gives you
more secure support for the bearings and seal. There seem to be decent
Grundfos too.

On 21/05/2017 12:11, John Rumm wrote:

I found a 35kW combi will do a pair of showers concurrently. Not going
to do 4 obviously - but its unlikely in a domestic setting that all 4
would be in use at exactly the same time.

Same findings here with a 36kW combi.

2 showers no problem. Biggest issue for me would be flow if another
tap/flush/washing-machine etc wanted water at the same time as we're
atop a hill and the waterboard won't up the pressure past 3.5 bar as it
causes problems for them down the bottom.

On 21/05/2017 11:43, The Natural Philosopher wrote:


To heat 15 l/min (an average single shower) from 5C to say 45C takes 42KW.

Average showers are targeted to deliver typically from 8 lpm these days.
15 lpm would be on the higher end for a normal shower mixer.

To fill a bath with water at 45C in 4 minutes is around 20l/min or 55KW.

For sure you can add a heat store to a combi at EVEN MORE EXPENSE to
give better figures than this, but that is pretty much what a DPHW
system IS.

My point is simple. Heating a house requires a constant low to medium
heat output over a long period of time. A boiler designed to do that
efficiently does not have the capability for a massive output over 4
minutes of the day when you want to fill a bath. Attempts to rectify
this with high power but modulating boilers etc simply make the boiler
more complex and costly.

Most modern (decent) system boilers have modulation anyway. Typically
the higher powered combis don't output the same power to the CH side
either. (my old 35kW Ideal Isar only delivered a maximum of 25kW to the
heating side).

The more complex solution is a thwacking great boiler.

Prices are similar, but even then, if you install the monster combi, you
can STILL only cope with one shower or bath at a time and you cannot
open a hot tap elsewhere.

Even a 35kW combi will feed two showers at once. Not as well as it will
do one, but still each will be better than an electric shower for example.

In short:

Installing a system boiler geared to the CH requirements and a DPHW tank
to provide peak flow of piping hot water gets you the optimal solution
to both problems,

I agree its a good system (its what I installed here). However it has
some of the same limitations as a combi. If you mains supply pressure or
flow rate is inadequate, then neither system will work well.

and is no more expensive than a small combi with a
large heat bank, or a large combi with no heat bank.

Not convinced. If you compare like with like kit there is not much
difference in price. If installing yourself so you don't need to cost
the labour, then there is not much in it. If paying for the
installation, then (depending on the starting situation) there may be a
fair amount of extra work for an unvented system.

And even a large combi can't meet the same peak demands that stored hot
water can.

That rather depends on your peak demand. The last combi I fitted was for
a place with one shower and no bath. (With no ideal location where a
cylinder could go). The 24kW combi met the peak demand with ease.

The only cheap option is a pathetically limited small combi with litle
or no heat bank.

Or a gravity fed cheap water tank with a system boiler.

That's not much cheaper than unvented by the time you add the cost of a
cistern even if the cylinder itself is a bit cheaper. However its better
suited to properties with low mains flow rates.

I have experienced both. They suck, big time,.

I also have experience of a variety of styles of system. However do not
find it so easy to make blanket Dr. Dribble style assertions. One needs
to look at the bigger picture.




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Mon, 22 May 2017 15:26:48 +0100
"www.GymRatZ.co.uk" wrote:

On 21/05/2017 12:11, John Rumm wrote:

I found a 35kW combi will do a pair of showers concurrently. Not
going to do 4 obviously - but its unlikely in a domestic setting
that all 4 would be in use at exactly the same time.

Same findings here with a 36kW combi.

2 showers no problem. Biggest issue for me would be flow if another
tap/flush/washing-machine etc wanted water at the same time as we're
atop a hill and the waterboard won't up the pressure past 3.5 bar as
it causes problems for them down the bottom.

Can they keep it at 3.5 bar whatever your usage? If so, then you should
have no problem.

--
Davey.

On 22/05/2017 17:05, Davey wrote:

Can they keep it at 3.5 bar whatever your usage? If so, then you should
have no problem.


When I had 2 showers going was before our recent building work so there
was a run from street to house of about 25m of 1970's black 1/2"(?)
pipe. When extension went up I re-routed a much shorter direct run to
the other side of the house where the boiler is situated in 25mm (20.5mm
bore), internal copper pipes are now 22mm so I'm hoping this will make a
difference if the main bathroom ever becomes more than the
concrete/block tool shed it's been for the last 5 years.
8¬o

On 21/05/2017 11:43, The Natural Philosopher wrote:
If you have an unpressurised tank you need pumped showers.

Point of information - only if the shower is upstairs. There's enough
head from a loft tank on the "2nd floor" to feed a shower on the ground
quite effectively.

Andy

In article ,
Vir Campestris wrote:
On 21/05/2017 11:43, The Natural Philosopher wrote:
If you have an unpressurised tank you need pumped showers.

Point of information - only if the shower is upstairs. There's enough
head from a loft tank on the "2nd floor" to feed a shower on the ground
quite effectively.

Andy

It does also depend on the pipework design as to how much restriction
there is. With a low head, you have to take much more care.

--
*Two wrongs are only the beginning *

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 22 May 2017 00:41:49 +0100, Davey wrote:

On Sun, 21 May 2017 19:38:25 +0100 mechanic
wrote:

On Sat, 20 May 2017 20:37:20 +0100, Andrew wrote:

It's called the laws of physics. The faster you move cold water
through the combi, the less heat is transferred into it from the heat
exchanger.

I think that the heat is still transferred, it just has to heat more
water in a given time, so the temp rise is less. Wherever you learned
the 'laws of physics' you should ask for your money back.

In fact, the faster you move cold water through the combi, the MORE heat
will be transferred, as there is always cold water coming along to take
away the heat. But with a greater volume of water, the temperature rise
is lower.

Is *exactly* the *right* answer! :-)

However, the increase in heat transfer will be only a percent or two
greater, if that[1]. The temperature drop, otoh, *is* likely to be
somewhat noticeable much to the discomfort of the shower cubicle occupant.

[1] Most of the temperature gradient between the plasma of the flame and
the water in the heat exchanger is between the fins and the plasma
itself, afaicr, somewhere in the region of hundreds of degrees C rather
than the tens of degrees between the fins in the flame plasma and the
inner walls of the heat exchanger in contact with the water itself.

A ten degree increase in temperature difference due to a lower water
temperature resulting from an increased water flow rate will be only a
very small percentage increase of the overall temperature difference
which allows heat energy of the flame to be transferred to the water.

Technically speaking, a higher water flow rate will extract a little
more heat energy from the flame plasma but this fact is unlikely be fully
appreciated when this results in a much cooler than expected showering
experience by the occupant of said shower cubicle.

--
Johnny B Good

On 26/05/17 23:07, Johnny B Good wrote:
he temperature drop, otoh,*is* likely to be
somewhat noticeable much to the discomfort of the shower cubicle occupant.

Years ago having a crap at the GFS house, got up to wash my hands and
screams of terror as it seemed from the upstairs shower 'Who's turned a
hot tap on'.

IT was of course the elder teenage daughter. Oddly we got to be good
mates after that.




--
Truth welcomes investigation because truth knows investigation will lead
to converts. It is deception that uses all the other techniques.

On 26/05/2017 23:15, The Natural Philosopher wrote:
On 26/05/17 23:07, Johnny B Good wrote:
he temperature drop, otoh,*is* likely to be
somewhat noticeable much to the discomfort of the shower cubicle
occupant.

Years ago having a crap at the GFS house, got up to wash my hands and
screams of terror as it seemed from the upstairs shower 'Who's turned a
hot tap on'.

IT was of course the elder teenage daughter.

One who doesn't understand plumbing. Turning a hot tap on would cool the
shower if anything.

--
Max Demian

On 27/05/17 12:45, Max Demian wrote:
On 26/05/2017 23:15, The Natural Philosopher wrote:
On 26/05/17 23:07, Johnny B Good wrote:
he temperature drop, otoh,*is* likely to be
somewhat noticeable much to the discomfort of the shower cubicle
occupant.

Years ago having a crap at the GFS house, got up to wash my hands and
screams of terror as it seemed from the upstairs shower 'Who's turned
a hot tap on'.

IT was of course the elder teenage daughter.

One who doesn't understand plumbing. Turning a hot tap on would cool the
shower if anything.

Eh? Thats exactly what it did. Turned her hot shower to a cold shower.,

Because the combi was total crap. Like every other combi i've come across

Except possibly the one installed in my sisters house in Germany that
was about the size of two minis stacked on top of each other.

In a well insulated 4 bedroom house...



--
Religion is regarded by the common people as true, by the wise as
foolish, and by the rulers as useful.

(Seneca the Younger, 65 AD)

On Sat, 27 May 2017 12:45:43 +0100, Max Demian wrote:

On 26/05/2017 23:15, The Natural Philosopher wrote:
On 26/05/17 23:07, Johnny B Good wrote:
he temperature drop, otoh,*is* likely to be
somewhat noticeable much to the discomfort of the shower cubicle
occupant.

Years ago having a crap at the GFS house, got up to wash my hands and
screams of terror as it seemed from the upstairs shower 'Who's turned a
hot tap on'.

IT was of course the elder teenage daughter.

One who doesn't understand plumbing. Turning a hot tap on would cool the
shower if anything.

Probably what the young lady was complaining about.