Hello,

I was browsing through some old posts and they said that 15mm pipe was
suitable for carrying up to 6kW according to one post and 9kW
according to another.

I'm a bit worried! It's very cold upstairs. We moved in last year and
the first thing we did was to insulate the loft. That hasn't been
enough, so I was going to change some radiators to bigger ones.

The thing is that the boiler has 22mm pipe come out of the boiler and
upstairs but on the landing this is reduced to 15mm which tees, with
one 15mm run going to the back rooms and one 15mm run going to the
front rooms. I am sure there must be more than 6kW of radiator
connected to that!

Is this why it's so cold? Will upgrading the rads. have no effect if
it is that the pipe cannot carry that capacity?

I'm not sure if it would be easy to change the pipe work without
ripping up the floor in each room. I would use plastic pipe to weave
through the joists. At the moment they've taken a big chunk out the
top of the joist to fit the two 15mm pipes through. That would be too
small to fit two 22mm pipes in, so I guess I'd be best to drill two
22mm holes in the middle of the joists. How far away from the existing
notch would I need to be to make sure I do not weaken the joist?

I also noticed that the gravity fed HW goes from the boiler in 28mm
pipe but is reduced in the airing cupboard to 22mm.

In both these cases, doesn't it defeat the object of using big pipe if
you then reduce it down later 22 to 15, or 28 to 22?

Thanks.

In article , Sam
writes
Hello,

I was browsing through some old posts and they said that 15mm pipe was
suitable for carrying up to 6kW according to one post and 9kW
according to another.

I'm a bit worried! It's very cold upstairs. We moved in last year and
the first thing we did was to insulate the loft. That hasn't been
enough, so I was going to change some radiators to bigger ones.

The thing is that the boiler has 22mm pipe come out of the boiler and
upstairs but on the landing this is reduced to 15mm which tees, with
one 15mm run going to the back rooms and one 15mm run going to the
front rooms. I am sure there must be more than 6kW of radiator
connected to that!

Is this why it's so cold? Will upgrading the rads. have no effect if
it is that the pipe cannot carry that capacity?

I'm not sure if it would be easy to change the pipe work without
ripping up the floor in each room. I would use plastic pipe to weave
through the joists. At the moment they've taken a big chunk out the
top of the joist to fit the two 15mm pipes through. That would be too
small to fit two 22mm pipes in, so I guess I'd be best to drill two
22mm holes in the middle of the joists. How far away from the existing
notch would I need to be to make sure I do not weaken the joist?

I also noticed that the gravity fed HW goes from the boiler in 28mm
pipe but is reduced in the airing cupboard to 22mm.

In both these cases, doesn't it defeat the object of using big pipe if
you then reduce it down later 22 to 15, or 28 to 22?


I'd say your first step is to balance the system, it is quite possible
that this has not been done correctly and radiators closer to the boiler
are stealing flow and therefore heat from the rest. Only if you cannot
achieve a satisfactory balance do you need consider redesign and
modification. The important thing is to go about it in a logical
progressive fashion and not make random changes in the hope of
improvement.

Here's a link for the uk.d-i-y group faq on radiator balancing:
http://www.diyfaq.org.uk/plumbing/rad-balance.html

Other useful; stuff he
http://www.diyfaq.org.uk/contents.html
and he
http://wiki.diyfaq.org.uk/index.php?...ecial:Allpages
but the balancing section there is still a skeleton in draft

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.
--
fred
Plusnet - I hope you like vanilla

fred wrote:
In article , Sam
writes
Hello,

I was browsing through some old posts and they said that 15mm pipe was
suitable for carrying up to 6kW according to one post and 9kW
according to another.

I'm a bit worried! It's very cold upstairs. We moved in last year and
the first thing we did was to insulate the loft. That hasn't been
enough, so I was going to change some radiators to bigger ones.

The thing is that the boiler has 22mm pipe come out of the boiler and
upstairs but on the landing this is reduced to 15mm which tees, with
one 15mm run going to the back rooms and one 15mm run going to the
front rooms. I am sure there must be more than 6kW of radiator
connected to that!

Is this why it's so cold? Will upgrading the rads. have no effect if
it is that the pipe cannot carry that capacity?

I'm not sure if it would be easy to change the pipe work without
ripping up the floor in each room. I would use plastic pipe to weave
through the joists. At the moment they've taken a big chunk out the
top of the joist to fit the two 15mm pipes through. That would be too
small to fit two 22mm pipes in, so I guess I'd be best to drill two
22mm holes in the middle of the joists. How far away from the existing
notch would I need to be to make sure I do not weaken the joist?

I also noticed that the gravity fed HW goes from the boiler in 28mm
pipe but is reduced in the airing cupboard to 22mm.

In both these cases, doesn't it defeat the object of using big pipe if
you then reduce it down later 22 to 15, or 28 to 22?


I'd say your first step is to balance the system, it is quite possible
that this has not been done correctly and radiators closer to the boiler
are stealing flow and therefore heat from the rest. Only if you cannot
achieve a satisfactory balance do you need consider redesign and
modification. The important thing is to go about it in a logical
progressive fashion and not make random changes in the hope of improvement.

Here's a link for the uk.d-i-y group faq on radiator balancing:
http://www.diyfaq.org.uk/plumbing/rad-balance.html

Other useful; stuff he
http://www.diyfaq.org.uk/contents.html
and he
http://wiki.diyfaq.org.uk/index.php?...ecial:Allpages
but the balancing section there is still a skeleton in draft

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.
Also check prior to balancing that each radiator is evenly warm from end
to end and top to bottom with not cold patches. This could indicated
sludge/partial blockages which need to be flushed out - possibly a
summer job but at least knowing about might avoid expensive radiator
upgrading.

Bob

On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.

Thanks. I could understand that but the reduction is size occurs
before the branches. The 28mm goes from the boiler to the airing
cupboard but before it gets to the cylinder changes to 22mm; there are
no branches on that it runs to the cylinder only. The CH goes from the
boiler in 22mm to the landing and splits into 15mm before that
branches. My other worry is that once it's branches, posts here said
15mm supports only 6kW. Surely one big rad could use all that up?

In article , Sam
writes
On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.

Thanks. I could understand that but the reduction is size occurs
before the branches. The 28mm goes from the boiler to the airing
cupboard but before it gets to the cylinder changes to 22mm; there are
no branches on that it runs to the cylinder only. The CH goes from the
boiler in 22mm to the landing and splits into 15mm before that
branches. My other worry is that once it's branches, posts here said
15mm supports only 6kW. Surely one big rad could use all that up?

Do you mean a single 22 reduces to a single 15, I ask as you say splits
into 15mm which suggests 22 splitting into 2 (or more) 15mm.

28mm dropping to 22mm for a short length is ok as (say) 8m of 28mm plus
2m of 22mm has less resistance to flow that 10m of 22mm.

The reduction to 15mm before the branches doesn't sound right but it may
still be a serviceable design, try the balance and if that doesn't sort
the problem then an upgrade to 22mm may be in order for a further part
of the run.

Gravity fed H/W is not my forte but the heating comments should still be
valid, I assume there is a separate pump and zone valve for the heating
circuit.
--
fred
Plusnet - I hope you like vanilla

In an earlier contribution to this discussion,
Sam wrote:

On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

In brief, on the subject reducing pipe sizes, thing of the pipework
as the a tree with a main trunk and smaller branches coming off the
main, once the trunk is split there's no need to have a full size
branch all the way to the top just to support a few leaves at the
end.

Thanks. I could understand that but the reduction is size occurs
before the branches. The 28mm goes from the boiler to the airing
cupboard but before it gets to the cylinder changes to 22mm; there are
no branches on that it runs to the cylinder only. The CH goes from the
boiler in 22mm to the landing and splits into 15mm before that
branches. My other worry is that once it's branches, posts here said
15mm supports only 6kW. Surely one big rad could use all that up?

It's a bl**dy big rad that will produce 6kW of output. Tell us the size and
construction (single, double, with/without fins) of each of your rads, and
we will calculate the approx output of each.

You then need to calculate the heat losses of each room, and see whether the
radiator capacity is adequate. You also need to calculate the *total* heat
losses, plus an allowance for hot water to see whether the boiler is
adequate.

If the design is ok, it is then simply(!) a matter of making sure that the
system is balanced properly and is not sludged up.

In the rooms which are not warm enough, how hot are the rads getting? [Best
measured with a infra-red thermometer but - failing that - for how long can
you hold your hand on the rad? If you feel the inlet and outlet pipes, is
the outlet a *lot* cooler than the inlet? Are the rads hot all over, or is
there a cooler region in the centre towards the bottom?

How is the boiler stat set? If it's a gravity HW system, is there any
control of HW temperature - other than by adjusting the boiler stat? If not,
chances are that the boiler is set at only about 60 degC - whereas you need
it at 80 to get more heat out of the radiators. [But then, the HW will get
too hot!]
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sat, 12 Jan 2008 13:27:10 +0000, fred wrote:

In article , Sam
writes
On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.

Thanks. I could understand that but the reduction is size occurs before
the branches. The 28mm goes from the boiler to the airing cupboard but
before it gets to the cylinder changes to 22mm; there are no branches on
that it runs to the cylinder only. The CH goes from the boiler in 22mm
to the landing and splits into 15mm before that branches. My other worry
is that once it's branches, posts here said 15mm supports only 6kW.
Surely one big rad could use all that up?

Do you mean a single 22 reduces to a single 15, I ask as you say splits
into 15mm which suggests 22 splitting into 2 (or more) 15mm.

28mm dropping to 22mm for a short length is ok as (say) 8m of 28mm plus
2m of 22mm has less resistance to flow that 10m of 22mm.

The reduction to 15mm before the branches doesn't sound right but it may
still be a serviceable design, try the balance and if that doesn't sort
the problem then an upgrade to 22mm may be in order for a further part
of the run.

Gravity fed H/W is not my forte but the heating comments should still be
valid, I assume there is a separate pump and zone valve for the heating
circuit.

No one's mentioned, yet, what the temperature from the boiler is.
There are such lot of basic simple stuff before we get into the subtle
stuff.
1) Is the primary flow form the boiler touchable?
2) Are all the radiators hot?
3) Are all the radiators hot all over?


--
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

On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

I'd say your first step is to balance the system, it is quite possible
that this has not been done correctly and radiators closer to the boiler
are stealing flow and therefore heat from the rest. Only if you cannot
achieve a satisfactory balance do you need consider redesign and
modification.

Thanks. Looks like I'm off to buy an IR thermometer then. Problem is,
they cost as much as a small radiator ;(

In article , Sam
writes
On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

I'd say your first step is to balance the system, it is quite possible
that this has not been done correctly and radiators closer to the boiler
are stealing flow and therefore heat from the rest. Only if you cannot
achieve a satisfactory balance do you need consider redesign and
modification.

Thanks. Looks like I'm off to buy an IR thermometer then. Problem is,
they cost as much as a small radiator ;(

Get a feel for it by hand then, inlet should be hotter than you can bear
to touch for any length of time, outlet should be less so, perhaps
bearable for 15s (if you're butch). If any outlets are at the same or
close in temp to the inlets then the rad needs throttling.

Obviously this is a very rough guide but it's a start and better than
(potentially) nothing at all.
--
fred
Plusnet - I hope you like vanilla

Hi. Thanks for the informative replies; I had so many, I didn't know
which one to quote.

I have ordered an IR thermometer courtesy of a well-know auction site
as this will be the quickest and easiest way to measure the
temperatures and check the system is balanced. Like someone said, a
little money spent on the thermometer now might save money on upgrades
later.

I made a mistake by mixing my BTUs and kWs. The larger radiators at
Screwfix have outputs of 6000ish BTUs, which is 2kW-ish; I was
thinking they were 6kW radiators. My mistake, sorry. So I have more
capacity in my pipe than I thought, which is good news.

The radiators in the house are old, single, without fins, and painted
over. Heat outputs unknown.

It's getting a bit late, so I'll reply to Fred's questions in the
morning. Good night.

The message
from Sam contains these words:

The radiators in the house are old, single, without fins, and painted
over. Heat outputs unknown.

Stelrad single panel?

23" high.

88" long 5921 Btus/hour.
82" 5498
76" 5075
69" 4652
63" 4229
57" 3808
50" 3384
44" 2961

--
Roger Chapman

In an earlier contribution to this discussion,
Roger wrote:

The message
from Sam contains these words:

The radiators in the house are old, single, without fins, and painted
over. Heat outputs unknown.

Stelrad single panel?

23" high.

88" long 5921 Btus/hour.
82" 5498
76" 5075
69" 4652
63" 4229
57" 3808
50" 3384
44" 2961

At what Delta-T value?

Those outputs look a bit optimistic to me - even at a delta-T of 60 degC
(140 degF) my calcs come out a bit lower than that.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

The message
from "Roger Mills" contains these words:

Stelrad single panel?

23" high.

88" long 5921 Btus/hour.
82" 5498
76" 5075
69" 4652
63" 4229
57" 3808
50" 3384
44" 2961

At what Delta-T value?

Those outputs look a bit optimistic to me - even at a delta-T of 60 degC
(140 degF) my calcs come out a bit lower than that.

Figures were taken from the Ravensbourne Guide to D.I.Y. Central
Heating. It is not dated but I think it is perhaps circa 1975 judging by
the prices and my contacts with the firm. It doesn't say how the figures
are calculated but a later offering from Ravensbourne (probably circa
1988) does state "Manufacturers give emission figures for each radiator
at a temperature difference between water and room of 60C or 108F".

The 88" radiator above gives 2.93 btus/sq. inch. The later catalogue
give the closest Barlow radiator - 24*84 as 6105 which at 3.02 btus/sq.
inch is higher but might not be significantly so as Stelrads dimensions
include the seam top and bottom and the Barlow is a roll top. Ignore the
seams and the average output is likewise 3.02.

--
Roger Chapman

On Mon, 14 Jan 2008 14:13:01 GMT, Roger
wrote:

The message
from Sam contains these words:

The radiators in the house are old, single, without fins, and painted
over. Heat outputs unknown.

Stelrad single panel?

23" high.

88" long 5921 Btus/hour.
82" 5498
76" 5075
69" 4652
63" 4229
57" 3808
50" 3384
44" 2961

Sorry I haven't replied to this thread for a while, I shall try to do
so today or tomorrow. In the meantime can I ask one quick question:

Do I need 28mm pipe for central heating/hot water if the system is
pumped? Is it that 28mm is only for gravity fed systems? If there is a
pump in place, does 28mm offer any advantage over 22mm?

Thanks.

In an earlier contribution to this discussion,
Fred wrote:


Sorry I haven't replied to this thread for a while, I shall try to do
so today or tomorrow. In the meantime can I ask one quick question:

Do I need 28mm pipe for central heating/hot water if the system is
pumped? Is it that 28mm is only for gravity fed systems? If there is a
pump in place, does 28mm offer any advantage over 22mm?


28mm (or 1" Imperial in the 'old' days) is certainly needed for gravity
circulation in order to minimise flow resistance - 'cos convection doesn't
generate much pressure.

22mm is usually sufficient for pumped systems unless you have a very large
or very leaky house with a correspondingly large boiler. There's no
particular merit in using 28mm pipe unless you really need to. On the other
hand, if you're converting a gravity system to pumped, and some conveniently
located 28mm pipe is already installed, there's no point in *not* using it.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

The message
from Fred contains these words:

Sorry I haven't replied to this thread for a while, I shall try to do
so today or tomorrow. In the meantime can I ask one quick question:

Do I need 28mm pipe for central heating/hot water if the system is
pumped? Is it that 28mm is only for gravity fed systems? If there is a
pump in place, does 28mm offer any advantage over 22mm?

The larger the bore the more water can be pumped though and further but
in a normal pumped system you may not need 28 mm even if you have one
circuit serving the whole house.

My information is grossly out of date but the figures I have (taken from
Ravensbourne Beginners Guide to Central Heating) a

Length limits at maximum flow rates (3 feet/sec)

Tube size (mm) Max flow (gallons/hr Max length (feet)

15 105 80
22 240 120
28 390 175

And at those values the heat capacity and head loss a

BTUs/hr inches water gauge/foot run

15 21,000 0.90
22 48,000 0.60
28 78,000 0.41

--
Roger Chapman