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Why convert from a vented expansion header tank to a pressurised unvented system?
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Stephen
Sep 14, 2015, 1:44:51 PM9/14/15
to
My In-laws have an oil fired boiler that was fitted 40 years ago.
This is based on a pump with two motorised 2 port valves, one for the
hot water cylinder and the central heating.
There were of course two plastic tanks, one being the cold water tank
and the other being the expansion tank, both in the loft.
Now they hired a plumber to move the hotwater cylinder from one end of
the landing to the other.
The plumber has removed the expansion tank, put in a filling loop and an
expansion vessel so effectively converting the system to a pressurised
sealed system. There is of course a pressurised relief valve.
The 40 year old boiler is still present and still in use. The boiler in
question is a simple system boiler so none of this condensing or combi
stuff.
WHat I'd like to know is why did the plumber do this? What benefit is
there to be gained by doing such a conversion?
More to the point, is a 40 year old oil fired boiler designed to cope
with a pressurised system?
Stephen.
This is based on a pump with two motorised 2 port valves, one for the
hot water cylinder and the central heating.
There were of course two plastic tanks, one being the cold water tank
and the other being the expansion tank, both in the loft.
Now they hired a plumber to move the hotwater cylinder from one end of
the landing to the other.
The plumber has removed the expansion tank, put in a filling loop and an
expansion vessel so effectively converting the system to a pressurised
sealed system. There is of course a pressurised relief valve.
The 40 year old boiler is still present and still in use. The boiler in
question is a simple system boiler so none of this condensing or combi
stuff.
WHat I'd like to know is why did the plumber do this? What benefit is
there to be gained by doing such a conversion?
More to the point, is a 40 year old oil fired boiler designed to cope
with a pressurised system?
Stephen.
Stephen
Sep 14, 2015, 1:46:19 PM9/14/15
to
on tank pressure and the cold taps are on either tank pressure or mains
pressure.
NY
Sep 14, 2015, 2:24:19 PM9/14/15
to
"Stephen" <i_lov...@spam.com> wrote in message
news:kIDJx.474786$z21.2...@fx18.am4...
I'm not sure what the advantages and disadvantages are for converting the
central heating system to a pressurised system, but there are certainly
advantages in having the hot water system (whether hot water cylinder or
combi heat-on-demand) fed from the rising main rather than a tank in the
loft: it means that the hot and cold water are at the same pressure as they
come out of the taps which makes it a *lot* easier to mix them; with a
tank-fed system you often need the hot tap full on and the cold tap barely
open to get an acceptable combination for warm water.
I'm not sure whether new houses with hot water fed from the rising main need
larger 22 mm pipes for the hot water system, compared with 15 mm for cold,
so that saves on the cost of copper needed. That advantage doesn't apply if
an *existing* system is later converted, because it's not cost-effective to
rip out all the 22 mm and put in 15 mm!
Are new houses ever fitted with header-tanks for hot water and/or central
heating, or is it standard nowadays to fit pressurised?
As regards an existing boiler being suitable, I wonder how the maximum
pressure of water in a pressurised system (before the pressure relief valve
trips) compares with the head of water from the expansion tank which will
act as a pressure relief valve in that water won't flow into the expansion
tank until the system pressure exceeds that head of water pressure.
news:kIDJx.474786$z21.2...@fx18.am4...
central heating system to a pressurised system, but there are certainly
advantages in having the hot water system (whether hot water cylinder or
combi heat-on-demand) fed from the rising main rather than a tank in the
loft: it means that the hot and cold water are at the same pressure as they
come out of the taps which makes it a *lot* easier to mix them; with a
tank-fed system you often need the hot tap full on and the cold tap barely
open to get an acceptable combination for warm water.
I'm not sure whether new houses with hot water fed from the rising main need
larger 22 mm pipes for the hot water system, compared with 15 mm for cold,
so that saves on the cost of copper needed. That advantage doesn't apply if
an *existing* system is later converted, because it's not cost-effective to
rip out all the 22 mm and put in 15 mm!
Are new houses ever fitted with header-tanks for hot water and/or central
heating, or is it standard nowadays to fit pressurised?
As regards an existing boiler being suitable, I wonder how the maximum
pressure of water in a pressurised system (before the pressure relief valve
trips) compares with the head of water from the expansion tank which will
act as a pressure relief valve in that water won't flow into the expansion
tank until the system pressure exceeds that head of water pressure.
Roger Mills
Sep 15, 2015, 6:58:34 AM9/15/15
to
On 14/09/2015 18:44, Stephen wrote:
with the hot water cylinder in a different place, it might have been
difficult to connect the fill and vent pipes in a way which would ensure
that pumping over wouldn't occur.
I've still got a vented primary system (with a 25-year-old gas boiler
which would be happy with vented or unvented) and have no plans to
convert it any time soon.
Unvented systems do have certain advantages:
- no danger of pumping over
- less risk of getting air in the system
- less risk of cavitation
- less risk of a flood if there's a leak[1]
However, it's slightly easier to add inhibitor to vented systems - and
you don't have the complication of filling loops, expansion vessels and
PRVs.
You pays your money . . .
[1] In practice, the ball valves in a vented system's fill & expansion
tank often seize up due to infrequent use, so there may not be a flood
even when there is a leak.
--
Cheers,
Roger
____________
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Dave Plowman (News)
Sep 15, 2015, 9:40:24 AM9/15/15
to
In article <kIDJx.474786$z21.2...@fx18.am4>,
contents of the system, unlike an open tank fed from a ball valve. A
sealed system also can't pump over and introduce air - and air in the
water speeds up corrosion.
> More to the point, is a 40 year old oil fired boiler designed to cope
> with a pressurised system?
No reason why the pressure should be much greater than from a header tank.
--
*Why are they called apartments, when they're all stuck together? *
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
Stephen <i_lov...@spam.com> wrote:
> The plumber has removed the expansion tank, put in a filling loop and an
> expansion vessel so effectively converting the system to a pressurised
> sealed system. There is of course a pressurised relief valve.
> The 40 year old boiler is still present and still in use. The boiler in
> question is a simple system boiler so none of this condensing or combi
> stuff.
> WHat I'd like to know is why did the plumber do this? What benefit is
> there to be gained by doing such a conversion?
For a start, much easier to bleed the rads. Any leak limited to the
> The plumber has removed the expansion tank, put in a filling loop and an
> expansion vessel so effectively converting the system to a pressurised
> sealed system. There is of course a pressurised relief valve.
> The 40 year old boiler is still present and still in use. The boiler in
> question is a simple system boiler so none of this condensing or combi
> stuff.
> WHat I'd like to know is why did the plumber do this? What benefit is
> there to be gained by doing such a conversion?
contents of the system, unlike an open tank fed from a ball valve. A
sealed system also can't pump over and introduce air - and air in the
water speeds up corrosion.
> More to the point, is a 40 year old oil fired boiler designed to cope
> with a pressurised system?
--
*Why are they called apartments, when they're all stuck together? *
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
DerbyBorn
Sep 15, 2015, 11:40:43 AM9/15/15
to
Don't assume the plumber gave it any thought - he probably just did what he
normally does with the bits he has in his van.
normally does with the bits he has in his van.
Roger Mills
Sep 15, 2015, 11:45:59 AM9/15/15
to
On 15/09/2015 14:34, Dave Plowman (News) wrote:
> In article<kIDJx.474786$z21.2...@fx18.am4>,
> Stephen<i_lov...@spam.com> wrote:
>
>> More to the point, is a 40 year old oil fired boiler designed to cope
>> with a pressurised system?
>
> No reason why the pressure should be much greater than from a header tank.
>
It *is* likely to be higher. It will probably be around 2 bar when hot.
> In article<kIDJx.474786$z21.2...@fx18.am4>,
> Stephen<i_lov...@spam.com> wrote:
>
>> More to the point, is a 40 year old oil fired boiler designed to cope
>> with a pressurised system?
>
> No reason why the pressure should be much greater than from a header tank.
>
The header tank would need to be about 60' in the air to achieve the
same pressure. Even so, the boiler is unlikely to mind.
Dave Liquorice
Sep 16, 2015, 4:43:07 AM9/16/15
to
On Tue, 15 Sep 2015 11:59:11 +0100, Roger Mills wrote:
> You'd have to ask the plumber why he chose to do that. It may be that,
> with the hot water cylinder in a different place, it might have been
> difficult to connect the fill and vent pipes in a way which would ensure
> that pumping over wouldn't occur.
Could be but assuming that the primary return is still available
> You'd have to ask the plumber why he chose to do that. It may be that,
> with the hot water cylinder in a different place, it might have been
> difficult to connect the fill and vent pipes in a way which would ensure
> that pumping over wouldn't occur.
where the cylinder was they could have just been T'd into that with
6" or so of separation. Though TBH I'd be happier with the expansion
connected to the flow from the boiler and the feed into the return,
both at the boiler. One assumes that they were connectd to the
flow/return of the primary at the cylinder.
What the plumber has done was almost certainly the quickest for him.
Time is money...
The boiler is probably specced up to 10 bar or was 40 years ago.
Might be worth a look on the SEBUK site for that boiler and find it's
notional effciency. It might be one that qualifies for a subsidised
replacement. You can get condensing system boilers but the gotcha is
that to run in condensing mode the primary has to be at a lower
temperature which may mean the radiators are now a bit undersized.
--
Cheers
Dave.
Dave Plowman (News)
Sep 16, 2015, 10:20:33 AM9/16/15
to
In article <nyyfbegfubjuvyypb...@srv1.howhill.co.uk>,
were quite specific - it had to be used in a sealed system. Which meant
running in a cold supply to it, so more work than sticking with the
existing header tank.
--
*Stable Relationships Are For Horses.
Dave Liquorice <allsortsn...@howhill.com> wrote:
> > You'd have to ask the plumber why he chose to do that. It may be that,
> > with the hot water cylinder in a different place, it might have been
> > difficult to connect the fill and vent pipes in a way which would ensure
> > that pumping over wouldn't occur.
> Could be but assuming that the primary return is still available
> where the cylinder was they could have just been T'd into that with
> 6" or so of separation. Though TBH I'd be happier with the expansion
> connected to the flow from the boiler and the feed into the return,
> both at the boiler. One assumes that they were connectd to the
> flow/return of the primary at the cylinder.
> What the plumber has done was almost certainly the quickest for him.
> Time is money...
It would depend on lots of things. But my Viessmann boiler instuctions
> > You'd have to ask the plumber why he chose to do that. It may be that,
> > with the hot water cylinder in a different place, it might have been
> > difficult to connect the fill and vent pipes in a way which would ensure
> > that pumping over wouldn't occur.
> Could be but assuming that the primary return is still available
> where the cylinder was they could have just been T'd into that with
> 6" or so of separation. Though TBH I'd be happier with the expansion
> connected to the flow from the boiler and the feed into the return,
> both at the boiler. One assumes that they were connectd to the
> flow/return of the primary at the cylinder.
> What the plumber has done was almost certainly the quickest for him.
> Time is money...
were quite specific - it had to be used in a sealed system. Which meant
running in a cold supply to it, so more work than sticking with the
existing header tank.
--
*Stable Relationships Are For Horses.
John Rumm
Sep 16, 2015, 12:36:02 PM9/16/15
to
On 14/09/2015 18:44, Stephen wrote:
> The plumber has removed the expansion tank, put in a filling loop and an
> expansion vessel so effectively converting the system to a pressurised
> sealed system. There is of course a pressurised relief valve.
>
> The 40 year old boiler is still present and still in use. The boiler in
> question is a simple system boiler so none of this condensing or combi
> stuff.
>
> WHat I'd like to know is why did the plumber do this? What benefit is
> there to be gained by doing such a conversion?
From the sealed system FAQ:
> expansion vessel so effectively converting the system to a pressurised
> sealed system. There is of course a pressurised relief valve.
>
> The 40 year old boiler is still present and still in use. The boiler in
> question is a simple system boiler so none of this condensing or combi
> stuff.
>
> WHat I'd like to know is why did the plumber do this? What benefit is
> there to be gained by doing such a conversion?
http://wiki.diyfaq.org.uk/index.php?title=Sealed_system_FAQ
"The advantages of sealed systems are at least the following:
They are simpler to install since there is no header tank in the
roof space and any of its possible problems such as over-flowing or
freezing.
They are easier to fill since air is expelled under pressure when
bleeding the radiators.
There can be no problems that stem from a number of installation
faults occurring on open systems that end up drawing air into the system
causing air locks, corrosion and sludge.
The increased pressure raises the boiling point of water in the
boiler. In an older boiler hot-spots cause localised boiling that often
make kettle-like noises or even loud clanks or bangs.
In the unlikely event of major damage to the heating system the
resulting flood is limited. In contrast with a conventional system where
the automatic top-up on the header tank will contribute an indefinite
amount.
They save space in flats where there is usually no good location
for the header tank anyway.
The system can be flushed out under pressure using the mains water
supply.
In fairness the following are slight draw backs:
It is a bit harder to introduce chemicals (such as inhibitors and
cleansers).
The system pressure needs checking from time to time.
> More to the point, is a 40 year old oil fired boiler designed to cope
> with a pressurised system?
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
NY
Sep 16, 2015, 1:53:06 PM9/16/15
to
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:LeidnWgx4YTwB2TI...@brightview.co.uk...
Digressing slightly, is there a similar list of advantages and disadvantages
for a hot water system as opposed to a central heating system, comparing
those fed from the rising main (ie hot water comes out of tap at rising main
pressure) versus those that use a header tank, either in the loft or (in the
case of my first house) in a tank that is joined on to the top of the hot
water cylinder.
What is normal practice / building regs for a new house: are mains-fed hot
water and sealed central heating more or less standard these days, or are
any new houses (or brand new installations in existing houses) still fitted
with header/expansion tanks?
news:LeidnWgx4YTwB2TI...@brightview.co.uk...
for a hot water system as opposed to a central heating system, comparing
those fed from the rising main (ie hot water comes out of tap at rising main
pressure) versus those that use a header tank, either in the loft or (in the
case of my first house) in a tank that is joined on to the top of the hot
water cylinder.
What is normal practice / building regs for a new house: are mains-fed hot
water and sealed central heating more or less standard these days, or are
any new houses (or brand new installations in existing houses) still fitted
with header/expansion tanks?
John Rumm
Sep 16, 2015, 7:53:14 PM9/16/15
to
http://wiki.diyfaq.org.uk/index.php?title=Unvented_DHW#Advantages_of_Unvented_cylinders
> What is normal practice / building regs for a new house: are mains-fed
> hot water and sealed central heating more or less standard these days,
> or are any new houses (or brand new installations in existing houses)
> still fitted with header/expansion tanks?
build market. Combis are popular in the low end. I don't know how many
conventional gravity / vented systems still get installed.
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