Hi Folks,

I need your advice on a combi boiler size. Let me describe my
situation:

I live in 2-bed, 1-bath semi-detached upper villa (1st floor and loft)
I plan to upgrade whole CH this summer by replacing boiler, pipework,
radiators and controls.
I know with combis it's flow rate and mains pressure that really
matters. I measured all that:

flow rate: 28 ltr/min
static pressu 3.0 bar
dynamic pressu 1.5 bar (with one tap open)

I have 22mm copper gas pipe from meter point and I reckon it could be
routed so that it will not exceed 16m in length between meter and
boiler. I also have gas hob and fireplace in the proximity of a boiler
(3-5m).

My question is:

1) Can I have Vaillant Ecotec 837 boiler and hob + fireplace fed off
my current gas supply or should I rather go for Ecotec 831 ? I only
have one bathroom but still would like to make the most of the flow
rate.

or ...

2) If I wanted to upgrade my gas supply to 28mm what would that mean
financially ? Has anyone done it ?

or ...

3) could I have Ecotec 837 without hob and fireplace (use electric
ones) ?

your help is much apprectated,

mike

wrote:
Hi Folks,

I need your advice on a combi boiler size. Let me describe my
situation:

I live in 2-bed, 1-bath semi-detached upper villa (1st floor and loft)
I plan to upgrade whole CH this summer by replacing boiler, pipework,
radiators and controls.
I know with combis it's flow rate and mains pressure that really
matters. I measured all that:

flow rate: 28 ltr/min
static pressu 3.0 bar
dynamic pressu 1.5 bar (with one tap open)

I have 22mm copper gas pipe from meter point and I reckon it could be
routed so that it will not exceed 16m in length between meter and
boiler. I also have gas hob and fireplace in the proximity of a boiler
(3-5m).

My question is:

1) Can I have Vaillant Ecotec 837 boiler and hob + fireplace fed off
my current gas supply or should I rather go for Ecotec 831 ? I only
have one bathroom but still would like to make the most of the flow
rate.

or ...

2) If I wanted to upgrade my gas supply to 28mm what would that mean
financially ? Has anyone done it ?

or ...

3) could I have Ecotec 837 without hob and fireplace (use electric
ones) ?

your help is much apprectated,

mike


Y'know. I posted here a few weeks ago about a man who wanted a decent
shower in a small place.

We assumed that the cheapest thing would be a combi,

Not.

In discussion with the plumber, it turned out that taking the old, but
perfectly serviceable boiler and coupling it to a mains pressure tank
and converting the rads to sealed Y plan would be the cheapest option of
all.

Indeed, when I looked at the cost of a sufficiently high output combi
(17Kw+) with the cost of a NEW uncased 10KW 'boilerhouse boiler' and
pressurized tank, there was sod all difference.

To the point where I am struggling to find any situation where a combi
is the best solution, or even the cheapest. Maybe a one bedroom flat of
tiny dimensions with no shower..but that's it.

Not wishing to put you off, just double check that what you are doing IS
the best cost-benefit..

I certainly have never met a combi yet that can match my peak hot water
flows here, with a pressurized tank.

Nor yet one that delivers full pressure hot water even when the power
goes out..well, for a while, anyway :-)

Or can have an immersion heater if you run out of oil or gas..

The Natural Philosopher wrote:

Indeed, when I looked at the cost of a sufficiently high output combi
(17Kw+) with the cost of a NEW uncased 10KW 'boilerhouse boiler' and
pressurized tank, there was sod all difference.

What would be typical products (and prices if possible) for us to look at?

wrote in message
ups.com...
Hi Folks,

I need your advice on a combi boiler size. Let me describe my
situation:

I live in 2-bed, 1-bath semi-detached upper villa (1st floor and loft)
I plan to upgrade whole CH this summer by replacing boiler, pipework,
radiators and controls.
I know with combis it's flow rate and mains pressure that really
matters. I measured all that:

flow rate: 28 ltr/min
static pressu 3.0 bar
dynamic pressu 1.5 bar (with one tap open)

I have 22mm copper gas pipe from meter point and I reckon it could be
routed so that it will not exceed 16m in length between meter and
boiler. I also have gas hob and fireplace in the proximity of a boiler
(3-5m).

My question is:

1) Can I have Vaillant Ecotec 837 boiler and hob + fireplace fed off
my current gas supply or should I rather go for Ecotec 831 ? I only
have one bathroom but still would like to make the most of the flow
rate.

or ...

2) If I wanted to upgrade my gas supply to 28mm what would that mean
financially ? Has anyone done it ?

or ...

3) could I have Ecotec 837 without hob and fireplace (use electric
ones) ?

Despite asking for advice you seem to have already made up your mind so now
you need to do the pipework calcs. Basically you asked about pipework gas
carrying capacity. The answer can be found here...

http://www.cda.org.uk/megab2/build/p...0Tube%20Sizing

I'm not going to do the calcs for you but one I did earlier suggests that
16m of (mainly) 28mm is not adequate for a 28kW boiler, cooker and stove.

Jim A

wrote:

I have 22mm copper gas pipe from meter point and I reckon it could be
routed so that it will not exceed 16m in length between meter and
boiler. I also have gas hob and fireplace in the proximity of a boiler
(3-5m).

Using the tables he

http://www.cda.org.uk/megab2/build/p...0Tube%20Sizing

You get a 15m run of 22mm pipe will give a max gas flow rate of about
3.4m^3/hour - and that assumes a straight run with the maximum allowed
pressure drop (1 mBar). Bends and elbows add more effective length to
the pipe.

My 35kW combi boiler claims to take a maximum gas rate of about 3.7m^3/hour

My question is:

1) Can I have Vaillant Ecotec 837 boiler and hob + fireplace fed off
my current gas supply or should I rather go for Ecotec 831 ? I only
have one bathroom but still would like to make the most of the flow
rate.

The short answer is no.

What power input is the boiler, hob, and fire? You may well be able to
get the specs from the makers web sites.

or ...

2) If I wanted to upgrade my gas supply to 28mm what would that mean
financially ? Has anyone done it ?

Your supply into the house is probably big enough (it runs at higher
pressure as well, so even if the pipe size looks no bigger than 22mm it
will have higher capacity). Hence the main cost is that of the pipe and
time to fit it.

or ...

3) could I have Ecotec 837 without hob and fireplace (use electric
ones) ?

That is a 37kW output boiler IIUC. So power input will be getting on for
41kW max, or 147.6MJ/hour. If you take a minimum natural gas energy
value as 37.5MJ/m^3 that could equate to 3.9m^/hour.

At that rate 12M (effective length) is your limit on 22mm pipe.

Which I guess answers your question.

28mm pipe would deliver upto 7m^3 at 15m, which is going to be adequate
I would have thought.

--
Cheers,

John.

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

Tim wrote:
The Natural Philosopher wrote:

Indeed, when I looked at the cost of a sufficiently high output combi
(17Kw+) with the cost of a NEW uncased 10KW 'boilerhouse boiler' and
pressurized tank, there was sod all difference.

What would be typical products (and prices if possible) for us to look at?

The best online deal I found for a stainless pressurised tank was a
Tempest something or other. Lifetime gurantee. About 650 quid for IIRC
150 liters. There were some slightly cheaper ones, but they didn't say
'stainless'; and didn't have a lifetime guarantee.

The plumber said 'Tempest? yeah. Done a few of those. Happy with that'
so that's the one we got.


I just googled like mad..also look up 'boilerhouse boilers'

I found a dainty little uncased one for £585..however in this case we
are using the existing boiler.

I did find sub £1k combis, but they were usually gas, and none were
really capable of more than about 10-15KW. since the friend was already
very unhappy with his 7KW electric shower, that didn't seem enough to me.

In the end the opportunity cost of the new hot water tank to the
existing boiler - which I didn't think was possible, but the plumber
said most definitely was - was below the cost of going to a combi.

and the final result was definitely better..the tank goes in the
boilerhouse, clearing a load of clutter from the bedroom. Which will
then be used to store the clothes currently hanging in a room off the
bedroom, which will be the ensuite shower.

"John Rumm" wrote in message
...
wrote:

I have 22mm copper gas pipe from meter point and I reckon it could be
routed so that it will not exceed 16m in length between meter and
boiler. I also have gas hob and fireplace in the proximity of a boiler
(3-5m).

Using the tables he

http://www.cda.org.uk/megab2/build/p...0Tube%20Sizing

You get a 15m run of 22mm pipe will give a max gas flow rate of about
3.4m^3/hour - and that assumes a straight run with the maximum allowed
pressure drop (1 mBar). Bends and elbows add more effective length to the
pipe.

My 35kW combi boiler claims to take a maximum gas rate of about
3.7m^3/hour

My question is:

1) Can I have Vaillant Ecotec 837 boiler and hob + fireplace fed off
my current gas supply or should I rather go for Ecotec 831 ? I only
have one bathroom but still would like to make the most of the flow
rate.

The short answer is no.

What power input is the boiler, hob, and fire? You may well be able to get
the specs from the makers web sites.

or ...

2) If I wanted to upgrade my gas supply to 28mm what would that mean
financially ? Has anyone done it ?

Your supply into the house is probably big enough (it runs at higher
pressure as well, so even if the pipe size looks no bigger than 22mm it
will have higher capacity). Hence the main cost is that of the pipe and
time to fit it.

or ...

3) could I have Ecotec 837 without hob and fireplace (use electric
ones) ?

That is a 37kW output boiler IIUC. So power input will be getting on for
41kW max, or 147.6MJ/hour. If you take a minimum natural gas energy value
as 37.5MJ/m^3 that could equate to 3.9m^/hour.

At that rate 12M (effective length) is your limit on 22mm pipe.

Which I guess answers your question.

28mm pipe would deliver upto 7m^3 at 15m, which is going to be adequate I
would have thought.

--
Maybe, maybe not. The 28mm upgrade I referred to retained 22mm near the
meter because I didn't fancy re-coring the wall.

0.43 of the allowable pressure drop occurs in that section and the 22mm
final leg to the boiler.

The lesson is the OP needs to do the calcs for his proposed installation and
it may be necessary to take 28mm as close to the meter as possible. Also I
said 28kW but the limiting boiler output for the installation is 33kW.

Jim A

guys - many thanks for all the useful comments, I now have much better
understanding of what can be achieved with what =)
I don't want to get into the battle which is better combi or tank? I
just want to understand requirements that I have to meet to install
both systems.

Basically you asked about pipework gas carrying capacity. The answer can be found here...
http://www.cda.org.uk/megab2/build/p...20Copper%20Tub...

yes exactly what I needed, thanks for that - I can now calculate gas
pipes and answer original question myself

What power input is the boiler, hob, and fire?

these are max gas requirements for applicances:
Vaillant 837 =~ 4.0 m3/h
Vaillant 831 =~ 3.3 m3/h
Cooker =~ 1.0 m3/h
Fireplace =~ 0.5 m3/h

so if I want 837 model I need to have 5.5 m3/h on some pipes between
meter and boiler.
points of interest a M(meter), B(boiler), F(fireplace), C(cooker)

M --- A --- D --- B
| |
C F

distances are effective (i.e. including tees and elbows), I have
calculated pressure drops from cda tables:
M-A 10m need 5.5 m3/h and 28mm pipe gives pressure drop of 10/25 =
0.40 mbar
A-D 3m need 4.5 m3/h and 28mm pipe gives pressure drop of 3/30 =
0.10 mbar
D-B 5m need 4.0 m3/h and 22mm pipe gives pressure drop of 5/12 =
0.42 mbar
A-C 3m need 1.0 m3/h and 15mm pipe gives pressure drop of 3/15 =
0.20 mbar
D-F 3m need 0.5 m3/h and 10mm pipe gives pressure drop of 3/9
= 0.33 mbar

total pressure drop from meter to appliances:
boiler (MA+AD+DB) = 0.40 + 0.1 + 0.42 = 0.92 mbar
cooker (MA+AC) = 0.40 + 0.20 = 0.60 mbar
fireplace (MA+AD+DF) = 0.40 + 0.1 + 0.33 = 0.83 mbar

all is within 1 mbar limit of pressure drop so should work ok. Please
could you sanity check my calculations and let me know if I am being
stupid ?

Your supply into the house is probably big enough (it runs at higher
pressure as well, so even if the pipe size looks no bigger than 22mm

The pipe coming out of a meter is 22mm. Can I (or rather CORGI man)
cut it just after the meter and expand it to 28mm ? Or do I have to
replace the whole meter ?

great group - thanks.

wrote in message
ps.com...
guys - many thanks for all the useful comments, I now have much better
understanding of what can be achieved with what =)
I don't want to get into the battle which is better combi or tank? I
just want to understand requirements that I have to meet to install
both systems.

Basically you asked about pipework gas carrying capacity. The answer can
be found here...
http://www.cda.org.uk/megab2/build/p...20Copper%20Tub...

yes exactly what I needed, thanks for that - I can now calculate gas
pipes and answer original question myself

What power input is the boiler, hob, and fire?

these are max gas requirements for applicances:
Vaillant 837 =~ 4.0 m3/h
Vaillant 831 =~ 3.3 m3/h
Cooker =~ 1.0 m3/h
Fireplace =~ 0.5 m3/h

so if I want 837 model I need to have 5.5 m3/h on some pipes between
meter and boiler.
points of interest a M(meter), B(boiler), F(fireplace), C(cooker)

M --- A --- D --- B
| |
C F

distances are effective (i.e. including tees and elbows), I have
calculated pressure drops from cda tables:
M-A 10m need 5.5 m3/h and 28mm pipe gives pressure drop of 10/25 =
0.40 mbar
A-D 3m need 4.5 m3/h and 28mm pipe gives pressure drop of 3/30 =
0.10 mbar
D-B 5m need 4.0 m3/h and 22mm pipe gives pressure drop of 5/12 =
0.42 mbar
A-C 3m need 1.0 m3/h and 15mm pipe gives pressure drop of 3/15 =
0.20 mbar
D-F 3m need 0.5 m3/h and 10mm pipe gives pressure drop of 3/9
= 0.33 mbar

total pressure drop from meter to appliances:
boiler (MA+AD+DB) = 0.40 + 0.1 + 0.42 = 0.92 mbar
cooker (MA+AC) = 0.40 + 0.20 = 0.60 mbar
fireplace (MA+AD+DF) = 0.40 + 0.1 + 0.33 = 0.83 mbar

all is within 1 mbar limit of pressure drop so should work ok. Please
could you sanity check my calculations and let me know if I am being
stupid ?

checked this using my spreadsheet and it seems to agree quite well. My
boiler calc says 0.44 + 0.09 + 0.44 = 0.97. The slight difference is
probably because I calculate and apply an exponential function from the
table. However I suggest you take into account any existing 22mm at the
meter it's not practicable to change. Anyway you have 5m of 22mm to play
with at the other end.

Still within spec but for many surprising just how close to the limit. Some
people (not me) even advocate 2 combis but I doubt he understands the calcs.

The pipe coming out of a meter is 22mm. Can I (or rather CORGI man)
cut it just after the meter and expand it to 28mm ?

yes

Or do I have to
replace the whole meter ?

unlikely

Jim A

checked this using my spreadsheet and it seems to agree quite well.
thanks Jim - much appreciated

boiler calc says 0.44 + 0.09 + 0.44 = 0.97. The slight difference is probably
because I calculate and apply an exponential function from the table.
yes - I have used nearest values from the table

However I suggest you take into account any existing 22mm at the
meter it's not practicable to change.
will do

The pipe coming out of a meter is 22mm. Can I (or rather CORGI man)
cut it just after the meter and expand it to 28mm ?
yes
excellent - thanks for clarifyng

mike

On Thu, 24 May 2007 09:44:56 +0100, The Natural Philosopher wrote:

Tim wrote:
The Natural Philosopher wrote:

Indeed, when I looked at the cost of a sufficiently high output combi
(17Kw+) with the cost of a NEW uncased 10KW 'boilerhouse boiler' and
pressurized tank, there was sod all difference.

What would be typical products (and prices if possible) for us to look at?

The best online deal I found for a stainless pressurised tank was a
Tempest something or other. Lifetime gurantee. About 650 quid for IIRC
150 liters. There were some slightly cheaper ones, but they didn't say
'stainless'; and didn't have a lifetime guarantee.

The plumber said 'Tempest? yeah. Done a few of those. Happy with that'
so that's the one we got.


I just googled like mad..also look up 'boilerhouse boilers'

I found a dainty little uncased one for £585..however in this case we
are using the existing boiler.

I did find sub £1k combis, but they were usually gas, and none were
really capable of more than about 10-15KW. since the friend was already
very unhappy with his 7KW electric shower, that didn't seem enough to me.

Most combis are sub £1k and most manufacturers make them from 24kW
(output) and upwards.


I presume that you have a good water main other wise the new tank may not
be as desired.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Thu, 24 May 2007 02:49:20 -0700, maciej.olchowik wrote:

guys - many thanks for all the useful comments, I now have much better
understanding of what can be achieved with what =)
I don't want to get into the battle which is better combi or tank? I
just want to understand requirements that I have to meet to install
both systems.



The pipe coming out of a meter is 22mm. Can I (or rather CORGI man)
cut it just after the meter and expand it to 28mm ? Or do I have to
replace the whole meter ?

great group - thanks.

You can obtain (although they may need to be ordered in) a true 1" or 28mm
gas meter union, with a full bore. A normal domestic gas meter can provide
64kW of gas, (6m^3/hr).

There is only a little pressure lost by having one fitting at a nominal
22mm/0.75" however the fitting is in the worst case location as all the
gas for the entire installation passes through it.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Thu, 24 May 2007 12:05:00 +0000, Jim Alexander wrote:

wrote in message
ps.com...
guys - many thanks for all the useful comments, I now have much better
understanding of what can be achieved with what =)
I don't want to get into the battle which is better combi or tank? I
just want to understand requirements that I have to meet to install
both systems.

Basically you asked about pipework gas carrying capacity. The answer can
be found here...
http://www.cda.org.uk/megab2/build/p...20Copper%20Tub...

yes exactly what I needed, thanks for that - I can now calculate gas
pipes and answer original question myself

What power input is the boiler, hob, and fire?

these are max gas requirements for applicances:
Vaillant 837 =~ 4.0 m3/h
Vaillant 831 =~ 3.3 m3/h
Cooker =~ 1.0 m3/h
Fireplace =~ 0.5 m3/h

so if I want 837 model I need to have 5.5 m3/h on some pipes between
meter and boiler.
points of interest a M(meter), B(boiler), F(fireplace), C(cooker)

M --- A --- D --- B
| |
C F

distances are effective (i.e. including tees and elbows), I have
calculated pressure drops from cda tables:
M-A 10m need 5.5 m3/h and 28mm pipe gives pressure drop of 10/25 =
0.40 mbar
A-D 3m need 4.5 m3/h and 28mm pipe gives pressure drop of 3/30 =
0.10 mbar
D-B 5m need 4.0 m3/h and 22mm pipe gives pressure drop of 5/12 =
0.42 mbar
A-C 3m need 1.0 m3/h and 15mm pipe gives pressure drop of 3/15 =
0.20 mbar
D-F 3m need 0.5 m3/h and 10mm pipe gives pressure drop of 3/9
= 0.33 mbar

total pressure drop from meter to appliances:
boiler (MA+AD+DB) = 0.40 + 0.1 + 0.42 = 0.92 mbar
cooker (MA+AC) = 0.40 + 0.20 = 0.60 mbar
fireplace (MA+AD+DF) = 0.40 + 0.1 + 0.33 = 0.83 mbar

all is within 1 mbar limit of pressure drop so should work ok. Please
could you sanity check my calculations and let me know if I am being
stupid ?

checked this using my spreadsheet and it seems to agree quite well. My
boiler calc says 0.44 + 0.09 + 0.44 = 0.97. The slight difference is
probably because I calculate and apply an exponential function from the
table. However I suggest you take into account any existing 22mm at the
meter it's not practicable to change. Anyway you have 5m of 22mm to play
with at the other end.

Still within spec but for many surprising just how close to the limit. Some
people (not me) even advocate 2 combis but I doubt he understands the calcs.

.... let alone that pressure drop is proportional to the square of the flow
rate, and inversely proportional to the forth power of pipe bore.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

Ed Sirett wrote:
On Thu, 24 May 2007 09:44:56 +0100, The Natural Philosopher wrote:

Tim wrote:
The Natural Philosopher wrote:

Indeed, when I looked at the cost of a sufficiently high output combi
(17Kw+) with the cost of a NEW uncased 10KW 'boilerhouse boiler' and
pressurized tank, there was sod all difference.
What would be typical products (and prices if possible) for us to look at?
The best online deal I found for a stainless pressurised tank was a
Tempest something or other. Lifetime gurantee. About 650 quid for IIRC
150 liters. There were some slightly cheaper ones, but they didn't say
'stainless'; and didn't have a lifetime guarantee.

The plumber said 'Tempest? yeah. Done a few of those. Happy with that'
so that's the one we got.


I just googled like mad..also look up 'boilerhouse boilers'

I found a dainty little uncased one for £585..however in this case we
are using the existing boiler.

I did find sub £1k combis, but they were usually gas, and none were
really capable of more than about 10-15KW. since the friend was already
very unhappy with his 7KW electric shower, that didn't seem enough to me.

Most combis are sub £1k and most manufacturers make them from 24kW
(output) and upwards.


I could not find any oil ones that cheap that did 20KW.

I presume that you have a good water main other wise the new tank may not
be as desired.


Not as good as we would like. 15mm feed. Pressure is good though. Think
we have about 3 bar or better here. And he is down the hill from me..4
maybe.

However all the new work will be 22mm and if time and money permits that
will be uprated back to the stopcock in a future upgrade.