Hi Andt,
To answer your queries:
1. The rads I mention are not as old as the antique types you mention
so I guess I mean old versions of more modern panel types.
2. I thought it was the typical triangle shape heat distribution but
it also sounds a bit like the top only and either end of rad heating
you suggested (I get the impression I am, not beong clear!)- when we
cleaned one out last year, it worked perfectly for a couple of weeks
before going back to the orignal useless heat distribution.
3. Yes, the new rads are in BTU/hr so I guess the existing pipes
should be ok. Phew.
I think we'll get a bloke round to change the rads and see how we get
on then. Fingers crossed it will be fine!
Thanks for the tips. You don't live near J9 of the M25 by any chance
do you? You sound like a very useful man to know!
Will keep you updated
Rebecca
Andy Hall wrote in message . ..
On 19 Aug 2003 11:06:53 -0700, (Rebecca) wrote:
Very useful information Andy. Thanks.
I wonder if a bit more info will narrow it down then...
Our house has a mixture of new and old steel rads. The new ones are
fine (not as hot as they could be but they heat up more or less
evenly), but the steel rads are heating very badly (only the top 2
inches)- despite us removing them last year and cleaning them
thoroughly (and cleaning the system with Fernox etc).
Sorry, Rebecca, just to be clear, when you talk about "old" rads, do
you mean the almost antique column types as in
http://www.tuscanfoundry.co.uk/subcategories.asp?cat=61
for example - i.e. the old cast iron types, or do you mean old
versions of more modern panel types?
Working out the expected heat output of the old cast iron types is
guesswork to some extent, but you could use the site I've mentioned
above and do a reasonable estimate based on sizes and design.
If they are the steel panel type but an older design, then try to find
something similar on the web sites of manufacturers like Myson,
Stelrad or Barlo.
You will sometimes notice that outputs are quoted per section for a
given type. All you then do is to take the number of sections for
your given radiator and multiply.
You will also notice that the output depends on the radiator type and
that with panel radiators you can have single or double panels and 0,1
or 2 sets of fins. These increase the output by increasing the
surface area that's hot.
If youu were saying that only the tops of the radiators in question
were hot but actually the cold area was more of a triangular shape at
the bottom, then this is normally an indication that there is sludge
in the bottom of the radiator. However if the hot area is at the top
and perhaps vertically at the end where the hot water enters, then it
is almost certainly inadequate flow for the radiator size.
That can be because the pipes are inadequate or partly blocked or the
system is way out of balance or that the pump is on too low a setting.
The situation can be exacerbated if you have some large radiators
relatively close to the boiler on the heating connections which are
connected with 15mm pipe and others further away on 8mm. Since the
flow will take the line of least resistance, the lockshield valves on
the 15mm connected radiators would typically need to be turned down a
fair way and those on 8mm connected radiators relatively open.
One thing you could do as a sanity check is to close the normal
control valves (or thermostatic valves) on all the radiators that are
getting hot and see whether the cold radiators improve substantially.
You could even close all but one. If there is a dramatic
improvement, you have a balance problem, otherwise it's pipes too
small, partial blocking or pump setting too low. You can easily
test pump setting by changing it and checking the effect - again with
the hotter radiators turned off.
Even if you did clean the radiators and put in Fernox, you could have
a partial block of pipes. This would involve flushing the system at
the radiator connections to check and clear for certain.
So, we were recommended to buy new rads to replace these old ones,
which we have done - I must admit the plumber who told us the sizes to
buy did guestimate. Looking at the B&G catalogue, the output of these
4 new rads ranges from 4500 to 6200. 3 of them are currently on 8mm,
and the smallest is on 6mm.
Do you mean 4500 to 6200 Watts here, Rebecca, or BTUs/hr?
One thing that irritates me about the heating industry is that they
persist in keeping the old BTU units; but the greater sin is that you
often see them mixed in specifications and designs. This is a recipe
for trouble because it's easy to make a numerical slip.
The conversion factor is 3412 BTUs/hr = 1kW.
So are the sizes you have bought really 4500W to 6200W or those
numbers in BTUs/hr? Manufacturer's data sheets normally have both.
These are pretty big radiators if they are in Watts and 8mm and
definitely 6mm would be woefully inadequate. If the numbers are in
BTUs/hr you are talking about 1.3kW and 1.8kW, which should be within
the range of 6mm and 8mm respectively as long as the pipes are no
longer than about 3-4 metres. Above these lengths, a proper
calculation of flow resistance ought to be done using tables for the
tube sizes. If you have that situation (e.g. if it's 10m or
something) then I can point you to the information.
From your figures Andy if the general rule of thumb applies, it looks
like we will have to replace most of the pipes (as 8mm generally deals
with up to 4500w). Have I interpreted this correct?
2500W for 8mm I think I said.
The plumber that recommended changing all the pipes to 15mm (but did
not recommend changing the rads) was the only one which was
recommended to us.
I think before you go to that trouble, there are some checks to do.
- First of all whether you can make a significant difference by
checking the system balance as described above - i.e. with turning off
radiators and playing with the pump speed.
-Even when the radiator is reasonably hot and several are working it's
worth checking the balance. You need a contact thermometer to do
this. The cheapest suitable form of these are boiler thermometers
which are a round dial type with a pointer and are held in place on
the pipe with a spring. B&Q and plumbers or heating merchants have
them for about £10. For doing a proper balancing adjustment
exercise, two are helpful but one will do to start with.
With the system running, measure the temperature of the flow pipe from
the boiler and then measure the return. You will probably find that
these rise as the boiler is firing and fall when its internal
thermostat turns off the burner. I would suggest taking the peak
values in this case. Then check the temperatures at each ends of
radiators. If any have a much higher return temperature than the
return at the boiler, you will know that the flow rate is
unnecessarily high through them. On the other hand, any that have a
lower return temperature, may not be receiving enough flow. If it's
way out, and you can bear your hand on the return pipes of the cooler
radiators then you know the flow is inadequate, but for temperatures
of more than about 55 degrees, you can't bear your hand on the surface
and it's not so easy to tell.
- To some extent, you can push more water through the smaller pipes by
increasing the pump setting. If this is effective, the affected
radiators will become warmer, as will their return pipes. However if
the pump becomes a lot noisier and you can hear the sound of water
movement more clearly at the affected radiators, it's a fair
indication that the pipes are inadequate or partly blocked. This is
why pipes are rated assuming a flow rate below 1.5metres/sec - to
avoid noise and turbulence in the pipes.
- If, let's say, you are able to fix the problem by checking balancing
(and you might), then there is a proper procedure in the group FAQ
(Phil Addison looks after this and posts a URL) on how to balance
properly.
There is still a big "however" though. You could completely cure
the warming of the radiators and the room(s) could still be
inadequately heated. I raise the point, because your older
radiators were of unknown output and one plumber has made a size
guesstimate.
You could run into a situation where the radiator output is simply not
enough for the room - the point is that radiators compensate for the
heat loss through the surfaces and due to air changes.
If you get to the point that it's pretty clear that new pipework is
needed, before you splash out on that, I would also check whether the
radiators are going to be big enough when they are working properly.
Unfortunately, some plumbers work by rule of thumb on this as well and
measure the volume of the house and divide by their auntie's telephone
number :-)
It is fairly easy to work out the heat requirement for a room using
software that you can download from the radiator manufacturer's web
sites (Barlo and Myson have good ones). Basically you have to
measure the walls, ceiling and floor and windows, and enter them into
the program while selecting what type of material they are. You also
put in the inside required temperature (e.g. 21 degrees for a living
room) and the outside (say worst case -3) and the likely number of air
changes per hour. You will get heat loss numbers for the room.
Basically, for a surface, the amount of heat loss through it depends
on the area, the temperature difference and a factor for the type of
material - you multiply these together for each surface and then add
the lot - the software does it for you.
It should be possible to do this exercise for a complete house in an
evening and could save some expensive mistakes of wrongly sizing
radiators. If you want to do this exercise, I've posted on it
before quite a bit.
Your opinion with this extra bit of info would be much appreciated!
Changing tac slightly 0 another plumber told us that we would have to
change the pipes coming form the boiler (some sort of Potterton) from
22mm to 28mm and that is why the circulation is bad. This sounds dodgy
to me...we had about 6 plumbers round and no-one mentioned this. What
do you think?
This is entirely possible, and is the opposite end of the same issue
that you might have with the radiators.
The boiler has a certain heat output, or normally a range of heat
outputs. In the same way that there must be adequate flow through a
radiator to achieve its specifiied output, there must be enough flow
through a boiler to get the heat away from it.
The results of inadequate pipe size are less immediately obvious,
though. If the problem is not too bad, all that will happen is that
the boiler's internal thermostat will shut the burner off for more of
the time during a heating cycle (room thermostat is demanding heat),
leaving the pump running. In more extreme cases, the boiler "short
cycles" which means that the burner might light for one minute and off
for two minutes etc. Basically this is because the burner is able to
deliver heat at a far greater rate than the water flow can take it
away.
Inadequate flow here can be because of inadequate pipe size at the
boiler, inadequate pump speed or because the flow through the
radiators is too low as a result of too many having inadequate pipe
sizes or part blocking or lockshield valves turned down too much.
To determine what the pipe size should be, it's necessary to know the
boiler output. Can you find the exact model number and ideally the
output rating in kW or BTU/hr? There are databases and
specifications around if you can only find the model number.
22mm tends to be the more common used for boilers in small to medium
sized older properties and small to relatively large newer properties.
If it's an older property and/or is fairly large (i.e. greater heat
loss) then 28mm might be needed.
Often though, the pipe runs immediately from the boiler are relatively
short before splitting for upstairs and downstairs connections, so
even if they are a bit undersized, it won't necessarily be the overall
limiting factor.
This is one to keep in mind, but I would check everything else first,
especially if some of the radiators are working properly.
Thanks
Rebecca
(Rebecca) wrote in message . com...
OK, I am so fed up with different plumbers and all their different
opinions. Can any of you help?
I have a very simple question and I hope its a straight forward
answer. I will miss out on the problem and suggested solutions and
hope this can be answered without the details.
Q Would you be happy keeping 8mm microbore thoughout your house (with
flow problems) or would you upgrade all to 15mm?
I realise that you may want more details but I'm not gonna give them.
This is the most basic difference 3 plumbers have told me.
No. 1 wants to change all pipes to 15mm
No. 2 wants to change only the 6mm pipe to 15mm
No. 3 wants to keep the 8mm
Please help. Its doing my head in!
Many thanks
Rebecca
.andy
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