This is sort of a followup to an earlier thread.

I have a floorstanding 20 y.o. gas Worcester Combi boiler (inherited from
previous owner). It has a heatbank internally and quite a high output
(130,000 btu I think). It feeds our aqualisa shower at fairly high
pressure/flow as long as nothing else is drawing a lot of presssure off (loo
cisterns are Ok, taps or WM nix). Incidentally it does have a motorised
valve (I had to replace the motor a few years back).

I was thinking about replacing it this year. It sounds like I have to do
this PDQ if I dont want a condenser?

Having read your FAQ, I am not at all sure I want a condensing boiler. All
our rads (19) have thermostatic valves. We like them this way as we have no
room thermostats and anyway we like to be able to change temperature of
individual rooms. Also I am not sure we can drain (see below).

I think I would go for a like-for-like as, although the combi has some
disadvantages, we have no desire to install roof tanks and cylinders.

My main concern is flueing. I really dont want to move the boiler* and it
currently uses a vertical flue through an adjacent chimney stack (liner/cap
etc.); problem is flue length is about 7.5m (3 story edwardian townhouse).
Many of the boilers I have looked up cant be given this length of flue.

The other thing is we would like it to be room sealed (ie draw air direct
from outside, but it doesnt have easy access to either outside wall or any
drain (solid floor) and internal door between boiler and ext wall.

Where does the drain on a condenser actually fit? I supposed within the
boiler itself? but maybe on flue??

Oh I should say I aim to get employ a pro to do all the work.

Excuse my ignorance and any good advice really appreciated.

Best wishes

Nick


* dont have anywhere alse nearly as suitable as current 'dead' floor space
between door and chimneybreast in utility room and dont want scary trouble
and expense of moving all the pipework (we have 3 rad zones plus HW)

-- Nick Holmes

Nick Holmes wrote:

I was thinking about replacing it this year. It sounds like I have to do
this PDQ if I dont want a condenser?

Unless you can score enough points on the assessment that would allow
you to fit a conventional boiler...

See he

http://www.odpm.gov.uk/stellent/grou...pdf_032807.pdf

Having read your FAQ, I am not at all sure I want a condensing boiler. All
our rads (19) have thermostatic valves. We like them this way as we have no
room thermostats and anyway we like to be able to change temperature of
individual rooms. Also I am not sure we can drain (see below).

Other than a room thermostat which ought to be fitted for any type of
boiler (and is a building regs requirement), none of the above preclude
the use of a condensing boiler, and having a condenser would not force
you to change the way in which you use the system (other than paying
less for gas of course)

My main concern is flueing. I really dont want to move the boiler* and it
currently uses a vertical flue through an adjacent chimney stack (liner/cap
etc.); problem is flue length is about 7.5m (3 story edwardian townhouse).
Many of the boilers I have looked up cant be given this length of flue.

Some will allow flue extensions to be run in plastic drainpipe (you can
do this with a condenser because the exhaust gas temperature is far lower)

The other thing is we would like it to be room sealed (ie draw air direct

Doubt you will get any choice in that, pretty much all the current
boilers have balanced (fan assisted) flues.

from outside, but it doesnt have easy access to either outside wall or any
drain (solid floor) and internal door between boiler and ext wall.

The flue air intake can be run with the exhaust (in fact most boilers
use a concentric pipe arrangement to achieve this)

Where does the drain on a condenser actually fit? I supposed within the
boiler itself? but maybe on flue??

It normally connects to the boiler along with the other pipes. The only
difference is that it is usually piped in plastic rather than copper.
With the addition of a pump the drain pipe can be routed pretty much
anywhere, so it can follow the existing HW or Heating pipe run if that
is convenient.

Oh I should say I aim to get employ a pro to do all the work.

So why ask on a DIY group then ;-))


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
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John Rumm wrote:
Nick Holmes wrote:

Oh I should say I aim to get employ a pro to do all the work.


So why ask on a DIY group then ;-))

Because quite a few pros hang out here? :-)

In article , John Rumm
wrote:
Nick Holmes wrote:

I was thinking about replacing it this year. It sounds like I have to do
this PDQ if I dont want a condenser?

Unless you can score enough points on the assessment that would allow
you to fit a conventional boiler...

See he

http://www.odpm.gov.uk/stellent/grou...breg_pdf_03280
7.pdf

Thank you very much for this reference; and for the rest of your very
helpful reply.

I am not sure if we would qualify. Most alternative locations for the
boiler or flue do not need to be considered under their exemptions. However
it is probably possible to resite it into the kitchen without either a 2m+
flue or a sump drain (940pts) - we might be able exclude this option under
one of the flue exclusions (if the flue plume would be less than 2.1m above
ground). This would however be v. expensive (major relocation of plumbing
and gas, destruction of custom kitchen units) and I havent got my head
around whether this would qualify. If we keep the location we dont exceed
the 1000 pts (890, the scores are cleverly constructed aren't they).

Having read your FAQ, I am not at all sure I want a condensing boiler. All
our rads (19) have thermostatic valves. We like them this way as we have no
room thermostats and anyway we like to be able to change temperature of
individual rooms. Also I am not sure we can drain (see below).

Other than a room thermostat which ought to be fitted for any type of
boiler (and is a building regs requirement), none of the above preclude
the use of a condensing boiler, and having a condenser would not force
you to change the way in which you use the system (other than paying
less for gas of course)

From what you say it sounds like I have misunderstood.

It seemed to me that a requirement of condensing boilers was that one
maintained an adequate temperature difference (e.g. 15-20 C) between the
output and input. If the rad valves close this wont be the case surely? At
present in our existing combi, the CH thermostat then cuts the gas so we get
quite a bit of cycling (unless weather is especially cold)

My main concern is flueing. I really dont want to move the boiler* and it
currently uses a vertical flue through an adjacent chimney stack (liner/cap
etc.); problem is flue length is about 7.5m (3 story edwardian townhouse).
Many of the boilers I have looked up cant be given this length of flue.

Some will allow flue extensions to be run in plastic drainpipe (you can
do this with a condenser because the exhaust gas temperature is far lower)

The other thing is we would like it to be room sealed (ie draw air direct

Doubt you will get any choice in that, pretty much all the current
boilers have balanced (fan assisted) flues.

That's good then.

from outside, but it doesnt have easy access to either outside wall or any
drain (solid floor) and internal door between boiler and ext wall.

The flue air intake can be run with the exhaust (in fact most boilers
use a concentric pipe arrangement to achieve this)

Yes I knew this, I think some are even flexible - which we would need to get
thro the chimney) - . In some cases there seems to an option for twin pipes,
which can run to different places which can allow longer fluing lengths. If
you had a separate air intake what are the rules on siting and termination?


Where does the drain on a condenser actually fit? I supposed within the
boiler itself? but maybe on flue??

It normally connects to the boiler along with the other pipes. The only
difference is that it is usually piped in plastic rather than copper.
With the addition of a pump the drain pipe can be routed pretty much
anywhere, so it can follow the existing HW or Heating pipe run if that
is convenient.

Yes, it looks like a pump will be our only option.

Oh I should say I aim to get employ a pro to do all the work.

So why ask on a DIY group then ;-))

Well, because there seem to be so many expert contributors. I did ask a
local engineer for advice and he proposed to fit a boiler which turned out
to have max concentric flue length of less than 4M. It could be that I am
wrong, but our site and requirements seem to be particularly tricky.

If anyone has recommendations for a really good heating engineer in Cambs....

Best wishes

Nick
--
Nick Holmes Division of Immunology, Dept of Pathology
Cambridge University, Cambridge CB2 1QP, UK
Tel:+44 1223 333871 Fax:+44 1223 333346
http://www-immuno.path.cam.ac.uk/~nh106/

Having read your FAQ, I am not at all sure I want a condensing boiler. All
our rads (19) have thermostatic valves. We like them this way as we have
no
room thermostats and anyway we like to be able to change temperature of
individual rooms.

You appear to be confused. A condensing boiler has no relevance to the TRVs
on the radiator. However, any modern boiler installation must bring the
controls up to modern standard. This, in particular, requires a "boiler
interlock", which is their way of saying that the boiler must entirely shut
down if the house is warm and not keep the pipes warm unnecessarily.

The two suggested methods are either a room thermostat, or some sort of flow
sensing on the circuit, with all radiators having a TRV. This is nothing to
do with condensing boilers. All oil or gas fired boilers must now have this
when installed and have done for some time.

My main concern is flueing. I really dont want to move the boiler* and it
currently uses a vertical flue through an adjacent chimney stack
(liner/cap
etc.); problem is flue length is about 7.5m (3 story edwardian townhouse).
Many of the boilers I have looked up cant be given this length of flue.

Many can. However, you are unlikely to get a modern boiler that will reuse
your old flue liner. There may be a few ancient inefficient and dangerous
open flued types you can get if you're quick.

The other thing is we would like it to be room sealed (ie draw air direct
from outside, but it doesnt have easy access to either outside wall or any
drain (solid floor) and internal door between boiler and ext wall.

There are some models of condensing boiler that can use cheap mPVC
drainpipes as their flueing system. You can poke both the exhaust and inlet
tubes up the existing chimney and attach the relevent terminals at the top.

This is only possible with condensing boilers, as conventional boilers have
hot exhausts that would melt the pipework. It helps if the existing flue is
straight, as the pipes can be dropped down the chimney pot without any
hassle.

Where does the drain on a condenser actually fit? I supposed within the
boiler itself? but maybe on flue??

Always on the boiler, but some flue routings require separate drainage as
well. This would not normally apply with an "up the chimney" routing. The
drain would be your biggest problem to solve. You may just be able to
channel a drain into the floor. You might even be able to pump the
condensate to the floor above and drain into the bathroom or something.

Christian.

Nick Holmes wrote:

I am not sure if we would qualify. Most alternative locations for the
boiler or flue do not need to be considered under their exemptions. However
it is probably possible to resite it into the kitchen without either a 2m+
flue or a sump drain (940pts) - we might be able exclude this option under
one of the flue exclusions (if the flue plume would be less than 2.1m above
ground). This would however be v. expensive (major relocation of plumbing
and gas, destruction of custom kitchen units) and I havent got my head
around whether this would qualify. If we keep the location we dont exceed
the 1000 pts (890, the scores are cleverly constructed aren't they).

you noticed that! ;-) Other than the issue of the condensate drain,
there is not much to be afraid of from having a condensing boiler. Many
of the usual objections people raise (increased complexity etc) apply to
most modern boilers regardless of whether they are condensers or not.

Other than a room thermostat which ought to be fitted for any type of
boiler (and is a building regs requirement), none of the above preclude
the use of a condensing boiler, and having a condenser would not force
you to change the way in which you use the system (other than paying
less for gas of course)


From what you say it sounds like I have misunderstood.

It seemed to me that a requirement of condensing boilers was that one
maintained an adequate temperature difference (e.g. 15-20 C) between the
output and input. If the rad valves close this wont be the case surely? At
present in our existing combi, the CH thermostat then cuts the gas so we get
quite a bit of cycling (unless weather is especially cold)

With traditional boiler designs, condensation was a "bad thing", and one
way to help ensure it did not happen, was to keep the return temperature
high enough. The condensing however does not have this limitation and
hence return temps _can_ be lower. However they do not *have* to be
lower - it is just that efficiency improves a bit more if they are.

Also modern condensers will have modulating burners, so instead of
running flat out until the demand is met, and then shutting off. They
will monitor the return temperature, and as they see it rise they will
reduce the gas rate to the burner. This way they can maintain their
preferred temperature drop without needing to cycle (unless the load
falls so low as to be under the minimum value it can modulate to). So
your rad valves won't have any negative impact when they shutdown
because the boiler will modulate to compensate for the reduced load.

(It is a bit like the argument that condensers run more efficiently at
lower flow temps than conventional designs, and hence when retrofitted
to an existing system will result in the radiators being undersized.
This is also a bit of a red herring because for most of the year it
won't be so cold for this to matter, and when it does, you can turn the
temperature up. You will lose some efficiency, but it will still be
better than the equivalent non condenser).

The flue air intake can be run with the exhaust (in fact most boilers
use a concentric pipe arrangement to achieve this)


Yes I knew this, I think some are even flexible - which we would need to get
thro the chimney) - . In some cases there seems to an option for twin pipes,
which can run to different places which can allow longer fluing lengths. If
you had a separate air intake what are the rules on siting and termination?

I don't think there are any special limitations on where the air intake
is sited... perhaps Ed or John would be able to confirm?


Oh I should say I aim to get employ a pro to do all the work.

So why ask on a DIY group then ;-))


Well, because there seem to be so many expert contributors. I did ask a

Sorry, my question was more intended as a rhetorical one, and not to be
taken quite that seriously ;-)

(Quite a number of recent posters seem to dive in with a pre-emptive
statement that they will "get a man in" to do it. Which is a little
ironic given that this group is one of the few places where most folks
are not going to raise an eyelid should you say you were doing all
yourself!)

local engineer for advice and he proposed to fit a boiler which turned out
to have max concentric flue length of less than 4M. It could be that I am
wrong, but our site and requirements seem to be particularly tricky.

ISTR that Kestron have been mentioned in the past for their particularly
flexible fluing arrangements. Perhaps that is one worth a look.



--
Cheers,

John.

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

It seemed to me that a requirement of condensing boilers was that one
maintained an adequate temperature difference (e.g. 15-20 C) between the
output and input. If the rad valves close this wont be the case surely?
At
present in our existing combi, the CH thermostat then cuts the gas so we
get
quite a bit of cycling (unless weather is especially cold)

There is no such requirement. The condensing boiler will be fine on any two
pipe radiator system whatsoever. There are various methods of optimising the
design of the radiator system for condensing operation, but this is not a
requirement and the condensing boiler will still be considerably more
efficient than the traditional boiler however it was designed.

Yes I knew this, I think some are even flexible - which we would need to
get
thro the chimney) - . In some cases there seems to an option for twin
pipes,
which can run to different places which can allow longer fluing lengths.
If
you had a separate air intake what are the rules on siting and
termination?

It varies. Typically, they can be independently run anywhere, but with a few
minor restrictions, like not terminating on opposite sides of the building.
Presumably they are worried that forced flow in a storm might not be
overcome by the boiler fan.

Christian.

On Fri, 11 Feb 2005 19:28:20 +0000, Nick Holmes
wrote:

This is sort of a followup to an earlier thread.

I have a floorstanding 20 y.o. gas Worcester Combi boiler (inherited from
previous owner). It has a heatbank internally and quite a high output
(130,000 btu I think). It feeds our aqualisa shower at fairly high
pressure/flow as long as nothing else is drawing a lot of presssure off (loo
cisterns are Ok, taps or WM nix). Incidentally it does have a motorised
valve (I had to replace the motor a few years back).

I was thinking about replacing it this year. It sounds like I have to do
this PDQ if I dont want a condenser?

Having read your FAQ, I am not at all sure I want a condensing boiler. All
our rads (19) have thermostatic valves. We like them this way as we have no
room thermostats and anyway we like to be able to change temperature of
individual rooms. Also I am not sure we can drain (see below).

I think I would go for a like-for-like as, although the combi has some
disadvantages, we have no desire to install roof tanks and cylinders.

My main concern is flueing. I really dont want to move the boiler* and it
currently uses a vertical flue through an adjacent chimney stack (liner/cap
etc.); problem is flue length is about 7.5m (3 story edwardian townhouse).
Many of the boilers I have looked up cant be given this length of flue.

The other thing is we would like it to be room sealed (ie draw air direct
from outside, but it doesnt have easy access to either outside wall or any
drain (solid floor) and internal door between boiler and ext wall.

Where does the drain on a condenser actually fit? I supposed within the
boiler itself? but maybe on flue??

Oh I should say I aim to get employ a pro to do all the work.

Excuse my ignorance and any good advice really appreciated.

Have a look at the Worcester-Bosch Greenstar Hiflow 440. It is
washing machine sized and floor standing. It is condensing but fluing
options are pretty flexible. It has a condensate pump so the outlet
for this can be above the boiler.

Mark.

In article , John Rumm
wrote:
Nick Holmes wrote:
From what you say it sounds like I have misunderstood.

It seemed to me that a requirement of condensing boilers was that one
maintained an adequate temperature difference (e.g. 15-20 C) between the
output and input. If the rad valves close this wont be the case surely? At
present in our existing combi, the CH thermostat then cuts the gas so we get
quite a bit of cycling (unless weather is especially cold)

With traditional boiler designs, condensation was a "bad thing", and one
way to help ensure it did not happen, was to keep the return temperature
high enough. The condensing however does not have this limitation and
hence return temps _can_ be lower. However they do not *have* to be
lower - it is just that efficiency improves a bit more if they are.

Also modern condensers will have modulating burners, so instead of
running flat out until the demand is met, and then shutting off. They
will monitor the return temperature, and as they see it rise they will
reduce the gas rate to the burner. This way they can maintain their
preferred temperature drop without needing to cycle (unless the load
falls so low as to be under the minimum value it can modulate to). So
your rad valves won't have any negative impact when they shutdown
because the boiler will modulate to compensate for the reduced load.

(It is a bit like the argument that condensers run more efficiently at
lower flow temps than conventional designs, and hence when retrofitted
to an existing system will result in the radiators being undersized.
This is also a bit of a red herring because for most of the year it
won't be so cold for this to matter, and when it does, you can turn the
temperature up. You will lose some efficiency, but it will still be
better than the equivalent non condenser).


Thank you very much John and Christian and Mark for you kind and helpful
replies.

You have allayed many of my concerns about condensing boilers.

I still believe that I may have a problem with draining, because of my site.

Incidentally, the Worcester HighFlow 440 that Mark mentioned does come with
an integral condensate drain pump but its max lift is 1.5m. It may also just
underpowered for our needs.


ISTR that Kestron have been mentioned in the past for their particularly
flexible fluing arrangements. Perhaps that is one worth a look.

Keston (if this is right) dont make a combi but you are right about thier
fluing (can be 50mm twin, separate air-in; exhaust of long run).

Incidentally, I do some DIY e.g. have replaced both the pump and diverter
valve motor on my existing boiler but I couldnt truly call myself competent
for gas regs purposes.

Best wishes

Nick
--
Nick Holmes

Nick Holmes wrote:

ISTR that Kestron have been mentioned in the past for their particularly
flexible fluing arrangements. Perhaps that is one worth a look.


Keston (if this is right) dont make a combi but you are right about thier
fluing (can be 50mm twin, separate air-in; exhaust of long run).

Yup, sorry no "r"... I have a feeling there have been threads on combis
that can drive a long flue in the past. Google ought to find them.

Incidentally, I do some DIY e.g. have replaced both the pump and diverter
valve motor on my existing boiler but I couldnt truly call myself competent
for gas regs purposes.

It seems to me there is a distinction to being a competent "gas fitter"
in the general sense, and being competent for one specific job. Assuming
you are not the former, it does not IMHO preclude you deciding you are
competent in the latter.

--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/