I'm eying up a 1970's house which has microbore heating pipes and rads,
conventional heating system with an old Baxi downstairs, HW tank in the
airing cupboard, cold and heating header tanks in the loft. Absolutely
no idea where the manifold is.

The radiators are ugly as hell and have some kind of valve which has
both feed and return pipes going into the same end of the rad. SWMBO
will definitely want them changed. If I'm changing all the rads at the
same time I might as well change the boiler to a combi to free up some
space (or possibly a pressurised HW tank) and get a decent shower.

Is it sensible to try and reuse the microbore, given the lack of access
to it, its age, and the fact that there must be some reason people
stopped using it 20 years ago, or should I plan to run a whole new set
of 15mm? Given the concrete floor, I'd probably end up running pipes in
the ceiling void, chased into walls, and behind the skirting,if that's
sensible.

Ben

Ben Blaukopf wrote:
I'm eying up a 1970's house which has microbore heating pipes and rads,
conventional heating system with an old Baxi downstairs, HW tank in the
airing cupboard, cold and heating header tanks in the loft. Absolutely
no idea where the manifold is.

The radiators are ugly as hell and have some kind of valve which has
both feed and return pipes going into the same end of the rad. SWMBO
will definitely want them changed. If I'm changing all the rads at the
same time I might as well change the boiler to a combi to free up some
space (or possibly a pressurised HW tank) and get a decent shower.

Is it sensible to try and reuse the microbore, given the lack of access
to it, its age, and the fact that there must be some reason people
stopped using it 20 years ago, or should I plan to run a whole new set

It depends.
The primary problem with microbore is that it can be hard to get enough
flow to keep the delta-t low for use with condensing boilers.

If you can't get the flow high enough, then you end up with either
some cool radiators, or the combi working at a higher temperature
than it'd like to for efficiency.

However.
I would be very surprised if you'd get another 5-10% out of the system
by replumbing in 22/15mm.
Can you have a look and see if the microbore is all the way back to the
boiler (very unlikely) or if there is 22/15mm piping to which it's
manifolded?

Ian Stirling wrote:
However.
I would be very surprised if you'd get another 5-10% out of the system
by replumbing in 22/15mm.
Can you have a look and see if the microbore is all the way back to the
boiler (very unlikely) or if there is 22/15mm piping to which it's
manifolded?

Just as a clue:
Our microbore manifold (70s installation in a 30s house) is under a
flase bottom in the airing cupboard (together with the pump, and near
the 3-position valve).

I looked for replacment "double entry" valves as the OP described, and
did find some (though didn't buy them) IIRC the manufacturer was IME
Yorkshire.


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On Wed, 31 Aug 2005 15:48:06 +0100, Ben Blaukopf
wrote:

I'm eying up a 1970's house which has microbore heating pipes and rads,
conventional heating system with an old Baxi downstairs, HW tank in the
airing cupboard, cold and heating header tanks in the loft. Absolutely
no idea where the manifold is.

There could be several - I have three.


The radiators are ugly as hell and have some kind of valve which has
both feed and return pipes going into the same end of the rad. SWMBO
will definitely want them changed.

This can be done quite easily by extending one pipe and hiding it
behind the radiator. Then you can put standard valves on each end.
There are numerous ways including 8 or 10mm versions of valves or
adaptors.



If I'm changing all the rads at the
same time I might as well change the boiler to a combi to free up some
space (or possibly a pressurised HW tank) and get a decent shower.

Usual health warning about checking that the mains water flow is
adequate, the gas supply is 22mm to the boiler and that a boiler
adequate for the smount and rate of HW you need is used.



Is it sensible to try and reuse the microbore, given the lack of access
to it, its age, and the fact that there must be some reason people
stopped using it 20 years ago, or should I plan to run a whole new set
of 15mm?

There's no reason to change it at all - in fact I've seen it used in
new houses recently.

If you are changing the boiler as well as the radiators, you can use
the opportunity to design the system to improve the efficiency of the
condensing boiler. Traditional systems are designed for CH flow and
return temperatures of 82 and 70 degrees. A condensing boiler will
operate in the same way when needed (in the depths of winter) but will
modulate down to a more efficient temperature at other times of the
year. However, you can make an improvement by designing around
temperatures of 70 and 50 degrees. This would entail choosing
radiators with approx 30% higher output ratings.

I did this exercise three years ago and was able to achieve these
objectives by moving some radiators to new positions and buying a
small number of higher output ones (e.g. twin panel and/or fins).

It's important to work out the outputs of the existing radiators and
then do a sanity check on the water carrying capacity of the pipes.
8mm pipe will transport about 1500W over a few metres and 10mm around
2500W. If you are reasonably close to being within these figures,
it should be fine.


Given the concrete floor, I'd probably end up running pipes in
the ceiling void, chased into walls, and behind the skirting,if that's
sensible.


I found that there was one case where the existing 8mm pipe was not
adequate for a new radiator and I swapped that out for 15mm. Apart
from that there was no significant change required except as
described. I would in any case make sure to flush the system
thoroughly. This can easily be done as you switch the system over to
sealed operation - you will have a mains supply and can flush out at
each radiator position. It's also important to fit a strainer filter
on the return to the boiler.





--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:

If you are changing the boiler as well as the radiators, you can use
the opportunity to design the system to improve the efficiency of the
condensing boiler. Traditional systems are designed for CH flow and
return temperatures of 82 and 70 degrees. A condensing boiler will
operate in the same way when needed (in the depths of winter) but will
modulate down to a more efficient temperature at other times of the
year. However, you can make an improvement by designing around
temperatures of 70 and 50 degrees. This would entail choosing
radiators with approx 30% higher output ratings.

I thought it was nearer 50% i.e. multiply specified (manufacturers) rad
output by 0.6 to get output when run at 70/50 degrees.

It's important to work out the outputs of the existing radiators and
then do a sanity check on the water carrying capacity of the pipes.
8mm pipe will transport about 1500W over a few metres and 10mm around
2500W. If you are reasonably close to being within these figures,
it should be fine.

also... :¬) my investigations lead me to believe that running 10
degrees lower with a -20 degree return (rather than traditional 10
degree difference) leads to greater heat capacity of pipes i.e double.
but all the above has been found on one single page on the eco-hometech
site so there may be diferences of opinions elsewhere.


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On Wed, 31 Aug 2005 20:34:31 GMT, "Pet @ www.gymratz.co.uk"
wrote:

Andy Hall wrote:

If you are changing the boiler as well as the radiators, you can use
the opportunity to design the system to improve the efficiency of the
condensing boiler. Traditional systems are designed for CH flow and
return temperatures of 82 and 70 degrees. A condensing boiler will
operate in the same way when needed (in the depths of winter) but will
modulate down to a more efficient temperature at other times of the
year. However, you can make an improvement by designing around
temperatures of 70 and 50 degrees. This would entail choosing
radiators with approx 30% higher output ratings.

I thought it was nearer 50% i.e. multiply specified (manufacturers) rad
output by 0.6 to get output when run at 70/50 degrees.

Looking at it again.. you're right - it is closer to 50%. Most
manufacturers specify 0.89 as the factor relative to EN442 tests for
82/70 and 0.6 for 70/50 (working on mean water to air temperatures.)
I was thinking what I did, and because the original system was
overspecified in most rooms, I was able to get away with less of an
increment after doing the heat loss calculations. However, as you
say, 50% would be better if using rule of thumb.




It's important to work out the outputs of the existing radiators and
then do a sanity check on the water carrying capacity of the pipes.
8mm pipe will transport about 1500W over a few metres and 10mm around
2500W. If you are reasonably close to being within these figures,
it should be fine.

also... :¬) my investigations lead me to believe that running 10
degrees lower with a -20 degree return (rather than traditional 10
degree difference) leads to greater heat capacity of pipes i.e double.
but all the above has been found on one single page on the eco-hometech
site so there may be diferences of opinions elsewhere.

This is true. You can work it out in this way:

- The amount of heat released by a volume of water cooling is
proportional to the mass of water and temperature fall.

- The limitation of pipes is the maximum linear flow rate for a given
size - generally the design recommendation is 1.5 metres/sec to
avoid excessive noise and flow resistance.

- It follows that mechanically, you can deliver a certain maximum mass
of water in a given time - and that is fixed regardless of temperature
(at least for what we are doing here.)

- Therefore, if we double the temperature drop at a given mean water
to air temperature, we double the amount of heat given up by the
water; or conversely for the same amount of heat, we only need half of
the volume, at that MWTA.

- It can be confusing when you think about the radiator size issue and
this together, but they are separate. In terms of the flow of energy
through the pipes, the radiator is irrelevant. The amount is governed
solely by flow rate and temperature drop.



--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:
On Wed, 31 Aug 2005 15:48:06 +0100, Ben Blaukopf
wrote:


I'm eying up a 1970's house which has microbore heating pipes and rads,
conventional heating system with an old Baxi downstairs, HW tank in the
airing cupboard, cold and heating header tanks in the loft. Absolutely
no idea where the manifold is.


There could be several - I have three.


The radiators are ugly as hell and have some kind of valve which has
both feed and return pipes going into the same end of the rad. SWMBO
will definitely want them changed.


This can be done quite easily by extending one pipe and hiding it
behind the radiator. Then you can put standard valves on each end.
There are numerous ways including 8 or 10mm versions of valves or
adaptors.




If I'm changing all the rads at the
same time I might as well change the boiler to a combi to free up some
space (or possibly a pressurised HW tank) and get a decent shower.


Usual health warning about checking that the mains water flow is
adequate, the gas supply is 22mm to the boiler and that a boiler
adequate for the smount and rate of HW you need is used.

Yep. I've made my offer on the house already, but I'll do a sanity check
with a jug and a stopwatch. Can't access the gas pipe to the boiler, but
it wouldn't be difficult to run a new one from the meter in any case. Do
gas meters ever come in a 15mm variety? I haven't actually checked in
the cabinet, but it's a standard external one set into the wall - I'll
have a poke in it when I go round with the surveyor.


Is it sensible to try and reuse the microbore, given the lack of access
to it, its age, and the fact that there must be some reason people
stopped using it 20 years ago, or should I plan to run a whole new set
of 15mm?


There's no reason to change it at all - in fact I've seen it used in
new houses recently.

Thanks, that's good to know.

If you are changing the boiler as well as the radiators, you can use
the opportunity to design the system to improve the efficiency of the
condensing boiler. Traditional systems are designed for CH flow and
return temperatures of 82 and 70 degrees. A condensing boiler will
operate in the same way when needed (in the depths of winter) but will
modulate down to a more efficient temperature at other times of the
year. However, you can make an improvement by designing around
temperatures of 70 and 50 degrees. This would entail choosing
radiators with approx 30% higher output ratings.

I did this exercise three years ago and was able to achieve these
objectives by moving some radiators to new positions and buying a
small number of higher output ones (e.g. twin panel and/or fins).

It's important to work out the outputs of the existing radiators and
then do a sanity check on the water carrying capacity of the pipes.
8mm pipe will transport about 1500W over a few metres and 10mm around
2500W. If you are reasonably close to being within these figures,
it should be fine.



Given the concrete floor, I'd probably end up running pipes in
the ceiling void, chased into walls, and behind the skirting,if that's
sensible.



I found that there was one case where the existing 8mm pipe was not
adequate for a new radiator and I swapped that out for 15mm. Apart
from that there was no significant change required except as
described. I would in any case make sure to flush the system
thoroughly. This can easily be done as you switch the system over to
sealed operation - you will have a mains supply and can flush out at
each radiator position. It's also important to fit a strainer filter
on the return to the boiler.

Do you actively flush the intermediate pipework, or simply check that
the water coming out of it looks reasonably clean? When I had my boiler
installed a couple of years ago I flushed out all the rads as per the
uk.d-i-y guide (written by you, I think?!) and just then just flushed
the pipes through with unpressurised water to check it came out clean.
Would I need to do more than this for microbore?

Anyway, sounds like I've got less work to do than I though then, plus or
minus some work with pen and paper.

Thanks

Ben

On Thu, 01 Sep 2005 10:12:02 +0100, Ben Blaukopf
wrote:



If I'm changing all the rads at the
same time I might as well change the boiler to a combi to free up some
space (or possibly a pressurised HW tank) and get a decent shower.


Usual health warning about checking that the mains water flow is
adequate, the gas supply is 22mm to the boiler and that a boiler
adequate for the smount and rate of HW you need is used.

Yep. I've made my offer on the house already, but I'll do a sanity check
with a jug and a stopwatch. Can't access the gas pipe to the boiler, but
it wouldn't be difficult to run a new one from the meter in any case. Do
gas meters ever come in a 15mm variety? I haven't actually checked in
the cabinet, but it's a standard external one set into the wall - I'll
have a poke in it when I go round with the surveyor.

No, the standard domestic meter is a U6, I believe, and is able to
deliver gas to the equivalent rate of 62kW. You do need to
calculate sizes and lengths of pipe to make sure that there is no more
than a 1mB pressure drop at the appliance(under full load) relative to
the pressure at the meter.

http://www.cda.org.uk/megab2/build/pub124/default.htm

is helpful to do the sums.





I found that there was one case where the existing 8mm pipe was not
adequate for a new radiator and I swapped that out for 15mm. Apart
from that there was no significant change required except as
described. I would in any case make sure to flush the system
thoroughly. This can easily be done as you switch the system over to
sealed operation - you will have a mains supply and can flush out at
each radiator position. It's also important to fit a strainer filter
on the return to the boiler.

Do you actively flush the intermediate pipework, or simply check that
the water coming out of it looks reasonably clean? When I had my boiler
installed a couple of years ago I flushed out all the rads as per the
uk.d-i-y guide (written by you, I think?!) and just then just flushed
the pipes through with unpressurised water to check it came out clean.
Would I need to do more than this for microbore?

For microbore (I have 8mm), I think that it would be better to use
pressurised water. I tried initially flushing using the old
arrangement of the loft tank. The system had had inhibitor in use
from new in 1985 and there was virtually no sludge in the radiators
and flow out of the microbore at each radiator outlet was OK but slow.

So, I did an initial flush using the roof tank with water being
allowed to exit first of all through the 22mm connections at the
boiler and then at radiator connections. I then installed the new
boiler with a strainer and isolating valves plus the new filling loop
etc.

The next step was to flush out under mains pressure at each radiator
valve with the boiler isolated. This completely cleared one side of
the system. A little more crud in the form of copper swarf (dark in
colour) from the original installation.

I then flushed with exit at the strainer (return side of boiler) so
that I know I had clean water at the boiler. Then I replaced the
strainer and opened boiler isolating valves and then flushed at each
radiator, thus cleaning out the flow side of the system.

So basically it can be done by planning order of work.

Given that you have an unknown system, I hink that it would be
sensible to assume that it hasn't been looked after and will need a
good flush.




Anyway, sounds like I've got less work to do than I though then, plus or
minus some work with pen and paper.

I think if it were me, if the system seems to be working OK now, I
would wait until next spring to do the changes. That way, you would
know from experience as well as calculation whether there are any
rooms that are inadequately heated or marginal.

Otherwise, I'd look at the existing radiators and measure them, find a
close equivalent from a manufacturer data sheet and work out what the
current outputs are. Then do the heatloss calculations for
comparison.



--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:

- It can be confusing when you think about the radiator size issue and
this together, but they are separate. In terms of the flow of energy
through the pipes, the radiator is irrelevant. The amount is governed
solely by flow rate and temperature drop.

:¬)

I am currently putting off the changing of radiators for bigger ones and
re-running 15mm _above_ solid concrete floor (damn 1970's bodges) untill
such time as it will become a priority due to having no heating in the
bedrooms.

Still, we can sleep on the sofa's upstairs where the UFH is working
sparkingly.

:¬)

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