I recall an experiment we did over 30 years ago. What restricts the heat
deliver to a radiators is the pump speed. Above a certain flow rate noise
is a problem. We used mainly 1/16 and 1/8" soft copper pipe to rads from
splayed manifolds and a high pressure pump. All calculated to get the heat
to the rads. To lessen noise no elbows would have to be used in the system
whatsoever. Noise was further reduced when equal sized pipes were used for
rads and straight rad valves were used, not the elbow type. The return pipe
did not have a rad valve. The pump had to be mounted with a flexible
connecting pipes and rubber mounted brass clips (a method I still recommend
today using pieces of plastic pipe or full braided connectors). It was
acceptable and the heat up times were zippo from cold. To improve
efficiency simple shelves were fitted over the rads. these diverted heat
into the room rather than it climbing up and warming the walls.
Thermometers on the outside walls proved this.
The problems were getting the installer to not use elbows in the 22mm runs
to the manifolds, which is very difficult in practice, and the ugliness of
the pipes entering the rads using straight rad valves. Some pipe clips
would be better being rubber mounted to reduce noise.
Things have moved on. Using plastic pipes, an auto variable speed pump and
rad valves in a U formation to direct the pipe behind the rads (and improve
looks) would make this system workable today. It is still easy to do by
having two auto variable speed pumps, one upstairs and one down making a
natural zoning system as well.
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But why would you do that unless you're an idiot? It's like running
a car and not being bothered to change or top up the oil. You'll get
away with it for a while and then have an expensive repair.
Do the sums. There is relatively little (typically <10-15) litres in
pipework. The main content is in the radiators.
That depends on the shape and layout of the pipework. Whether it is
microbore or not is not the issue. The only minor point is bringing
the pipes to common points, but if a distributed system is done in
22mm with 15mm branches, as long as sizing is done properly there
should be no difference.
Full boiler temperature goes to all radiators regardless of the system
unless the valves are turned off.
If you measure the flow temperature at the input of each radiator, it
will be at boiler temperature in seconds, regardless of pipe size.
The standard design criterion is for 1.5m/sec.
It will then take each radiator a rather longer time to become hot,
because the water has to be moved through it.
Since the rate of heat transfer is proportional to the flow rate, and
the pipework should be designed for adequate flow rate, then the rate
of heating will be dependent on the boiler output more than anything
It is misleading to believe that the pipe size, as long as it is
adequate has anything to do with rate of warming up.
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Slightly less volume of water in the system means it heats up slightly
quicker, but the main volume is in the rads anyway on most systems, so
it is as usual a case of IMM saying something he has read somewhere that
has been grossly exageratted by marketeers, and taking it as gospel
because he lacks the education to see through the con.
The only thing that you can say is that they are likely to be
installed in pairs on the flow and return pipes. It *may* be that
the pipes to a given radiator are of equal length to one another, but
that is no big deal since the flow resistance depends on the total
pipe length from one manifold through the radiator and back to the
other manifold. It is quite unlikely that the pipe pairs to
different radiators are equal to one another and it is also unlikely
that the radiators in different rooms are of equal size or heat
output. So in reality the manifolds are no more than a plumbing
I could accept that there is local fashion and misunderstanding, but I
don't see that the dH of the water has anything to do with it, or that
sealing or not has an impact either.
I do, and there is no magic in the way that you are trying to imply.
The water is not sentient and does not think to itself "Ah, a
manifold, I had better behave in a different way to when I am in a
system with 15mm tube."
Any form of constant pressure or flow would depend on equalities of
distance and radiator size and houses like this are featured only in
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However, there are some advantages to the manifold. In particular, there
will be the same pressure across each radiator/pipework combination. This
would make it harder for one radiator to steal all the pressure,
particularly if you have a low resistance radiator near the beginning of the
main 22mm run, meaning that the pressure drops substantially for subsequent
It's not the manifold itself, or the microbore that causes this, but having
independent pipes to each radiator from a common point. There are
disadvantages too, such as the much greater quantity of pipework required.
The microbore would provide an element of self balancing in that it will
ensure that there is always some pressure drop, so you don't short circuit
the system. The same effect could be had on a manifold 15mm based system by
simply having every lockshield open about a third. Indeed, it would probably
be better balanced than the microbore, as the resistance would be similar
for all radiators, rather than being dependent on pipe lengths.
Personally, I object to microbore, as in Reading, such a system would last
about 15 minutes before sludging to extinction. I think I would actually
quite like a star/manifold based system with no pipework sharing, though. It
would make implementing a seriously upgraded S-Plan system very appealing. I
wonder if you could get a discount for buying 8 zone valves and 8
programmable room stats? I would probably implement this way, if I was
installing my system from scratch and had all the floorboards up. Neither
applies to me, so I'll stick with one zone valve per floor (plus a blank
space for one more when I build the conservatory).
On Wed, 19 Nov 2003 11:34:38 -0000, "Christian McArdle"
The only effect really is that lengths of 8mm pipe offer a degree of
resistance to the flow. If you think about it in electrical terms
it is like a resistor network. You are putting a fixed resistor in
series with a variable one (the lockshield). This has the effect of
reducing the control range of the lockshield and in that sense
provides a degree of load sharing. In the case of the combination of
22mm with 15mm branches, you are connecting networks of fixed
resistors together in a different way. If the backbone were done in
28mm pipe instead the resistance in the backbone would tend to zero
and the flow rates would again be determined partly by the lockshield.
Having the microbore arrangement, does reduce the iteration process
needed when balancing because there are the equal pressure points as
you say. 22+15mm systems are only harder to balance because of the
sharing of radiators on lengths of 15mm pipe and possible inadequate
sizing of 22mm.
It is easier to run, however.
That's a matter of degree.
That's simply not true. I've had an open vented 8mm system in
Wokingham for 18 years and that has not been subject to sludging to
any extent at all. It is a different water supplier, but the
chemical composition is very similar to that of the People's Republic
(sorry City) of Reading.....
I agree. A zone valve/manifold system would be ideal.
I'm in the process of designing a control system with analog
controlled radiator valves which will balance and temperature control
in one operation using room and pipe temperature sensors.
Oh yes. They were rather put out when they didn't get city status last time.
Must be the only town in the country where all the buses (well half the
buses...) say "City Centre" on the destination. All the information boards
read "City Centre Car Parks Full/Spaces" too.
What a relief. Instred of IMM's veiled allusions a complete rational
To which my comment is 'true, but probably irrelevant'
UF heating is done this way anyway mostly - well mine is, and yes, it is
amenable to all that stuff, but it gets a bit irritating to implement.
The one thing I did enjoy tho, was being able to balance all the zones
*at the manifold* using the tiddly little flow meters on each branch.
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