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  #1   Report Post  
Lobster
 
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Default Preventing halogen lights overheating under Rockwool

Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

Thanks
David
  #2   Report Post  
G&M
 
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Default Preventing halogen lights overheating under Rockwool


"Lobster" wrote in message
om...
Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?


If your ceiling can take the weight, why not use the old style "clay"
underground pipes. You can pick them up for next to nothing and they
definitely won't burn.


  #3   Report Post  
Robert
 
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Default Preventing halogen lights overheating under Rockwool

In message , G&M
writes

"Lobster" wrote in message
. com...
Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?


If your ceiling can take the weight, why not use the old style "clay"
underground pipes. You can pick them up for next to nothing and they
definitely won't burn.

I used up-ended terracotta plant pots.
--
Robert
  #4   Report Post  
[news]
 
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Default Preventing halogen lights overheating under Rockwool


"Lobster" wrote in message
om...
Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

Thanks
David


http://tinyurl.com/2qmgl may be of use


  #5   Report Post  
Lurch
 
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Default Preventing halogen lights overheating under Rockwool

On 23 Jun 2004 12:02:06 -0700,
(Lobster) strung together this:

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

That's exactly I have done in the past, a perfect solution.
--

SJW
A.C.S. Ltd


  #6   Report Post  
rrh
 
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Default Preventing halogen lights overheating under Rockwool


Or you could cut lengths of 100mm diameter aluminium ducting hose.


  #7   Report Post  
David
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool


"Lobster" wrote in message
om...
Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

Thanks
David


I think what you have here pretty much covers the issue of isolating the
lights fom the rockwool but ideally you also want to minimise any path for
water vapour to enter the loft as well, especially as they are in the
bathroom. The design of the light fittings and how well they are installed
will play a part in this and obviously the current ventialation to the
bathroom will affect things..

Potentially you would expect more water vapour to get through using an open
pipe arrangement than using the old teracotta pot which can also be sealed
to some extent.

cheers

David





  #9   Report Post  
IMM
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool


"David" wrote in message
...

"Lobster" wrote in message
om...
Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

Thanks
David


I think what you have here pretty much covers the issue of isolating the
lights fom the rockwool but ideally you also want to minimise any path for
water vapour to enter the loft as well, especially as they are in the
bathroom. The design of the light fittings and how well they are

installed
will play a part in this and obviously the current ventialation to the
bathroom will affect things..

Potentially you would expect more water vapour to get through using an

open
pipe arrangement than using the old teracotta pot which can also be sealed
to some extent.


use plantpots, as these are cheap and fireproof. Seal up the hole if there
is one. Cut a notch in the rim for the cable and seal around the rim with
silicon.


  #10   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

IMM wrote:

Potentially you would expect more water vapour to get through using an

open
pipe arrangement than using the old teracotta pot which can also be sealed
to some extent.


use plantpots, as these are cheap and fireproof. Seal up the hole if there
is one. Cut a notch in the rim for the cable and seal around the rim with
silicon.

How does this help? The requirement is to stop the light getting too
hot, if you completely enclose it in a flower put and even seal it up
then it'll get even hotter won't it?

--
Chris Green


  #13   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In article , writes
wrote:
In article ,
writes
IMM wrote:

Potentially you would expect more water vapour to get through using an
open
pipe arrangement than using the old teracotta pot which can also be

sealed
to some extent.

use plantpots, as these are cheap and fireproof. Seal up the hole if there
is one. Cut a notch in the rim for the cable and seal around the rim with
silicon.

How does this help? The requirement is to stop the light getting too
hot, if you completely enclose it in a flower put and even seal it up
then it'll get even hotter won't it?

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.


Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?

Its keeping the rockwool away from the lamp, when I said that the lamps
go into enclosed spaces I didn't expect anybody to read that as its ok
to pack them in rockwool, its possible that packing them tight with
rockwool and then having that combination in close proximity to a joist,
rafter, boarding or anything else combustible could have potential for
trouble
--
David
  #15   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

IMM wrote:

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.


Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?


It is keeping an air space around the lamp and the insulation away from the
lamp too.

It may give you "warm feelings" (ha, ha!) but I fail to see what good
it's done for anything.

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.

The insulation won't care either way as it's decidedly not
inflammable.

The one thing it *might* do is protect adjacent joists from the heat of
the lamp but I'm not all that convinced that "no flowerpot" will make
the joist any warmer than "flowerpot" will.

The idea of a 'chimney' of some sort (i.e. a largeish tin with both
ends cut off) seema a much more sensible approach to me.

--
Chris Green


  #16   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In article , writes
IMM wrote:

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.

Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?


It is keeping an air space around the lamp and the insulation away from the
lamp too.

It may give you "warm feelings" (ha, ha!) but I fail to see what good
it's done for anything.

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.


This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so

The insulation won't care either way as it's decidedly not
inflammable.

The one thing it *might* do is protect adjacent joists from the heat of
the lamp but I'm not all that convinced that "no flowerpot" will make
the joist any warmer than "flowerpot" will.

The idea of a 'chimney' of some sort (i.e. a largeish tin with both
ends cut off) seema a much more sensible approach to me.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this
--
David
  #17   Report Post  
Will
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

On Mon, 28 Jun 2004 19:26:11 +0100,
wrote:

In article ,
writes
IMM wrote:

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.

Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?

It is keeping an air space around the lamp and the insulation away from the
lamp too.

It may give you "warm feelings" (ha, ha!) but I fail to see what good
it's done for anything.

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.


This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so



Light fittings are designed to give sufficient ventilation to
allow the lamp to run at its optimum temperature.

By altering the potential airflow - and thus the cooling
efficiency - of the fitting, you will cause the lamp to run in excess
of its optimum temperature, which will lead to premature failure. Not
to mention the premature failure of the fitting itself.

I can't say that I have noted the effect in low voltage lamps -
they are largely disposed to early failure anyway - though gls and
reflector lamps exhibit the same tendency...

--
Regards,

Will.


  #18   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In article , Will
writes
On Mon, 28 Jun 2004 19:26:11 +0100,
wrote:

In article ,
writes
IMM wrote:

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.

Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?

It is keeping an air space around the lamp and the insulation away from the
lamp too.

It may give you "warm feelings" (ha, ha!) but I fail to see what good
it's done for anything.

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.


This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so



Light fittings are designed to give sufficient ventilation to
allow the lamp to run at its optimum temperature.

By altering the potential airflow - and thus the cooling
efficiency - of the fitting, you will cause the lamp to run in excess
of its optimum temperature, which will lead to premature failure. Not
to mention the premature failure of the fitting itself.

I'm not sure if you are agreeing with me or not :-) I'm saying that
these type of lamps are designed to run in confined place so get all the
cooling they need without the addition of 'cooling chimneys,

I can't say that I have noted the effect in low voltage lamps -
they are largely disposed to early failure anyway - though gls and
reflector lamps exhibit the same tendency...


I have mine enclosed in upturned pots and can't say that mine fail any
earlier than anybody else's

--
David
  #19   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

wrote:
In article ,
writes
IMM wrote:

Is the requirement to stop them getting hot?? they are designed to go
into enclosed spaces not just open lofts so I don't think heat build up
around the lamps is a problem, the requirement is to keep materials away
from the lamp so an upturned clay pot is a good solution, I did this to
mine years ago without problem.

Well the original subject is "Preventing halogen lights overheating
under Rockwool". The loft insulation is hardly going to suffer from
the heat of the lamp so what good is the plant pot doing?

It is keeping an air space around the lamp and the insulation away from the
lamp too.

It may give you "warm feelings" (ha, ha!) but I fail to see what good
it's done for anything.

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.


This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so

But what's the point then?

The insulation won't care either way as it's decidedly not
inflammable.

The one thing it *might* do is protect adjacent joists from the heat of
the lamp but I'm not all that convinced that "no flowerpot" will make
the joist any warmer than "flowerpot" will.

The idea of a 'chimney' of some sort (i.e. a largeish tin with both
ends cut off) seema a much more sensible approach to me.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this


You are probably also doing something awful to the fire proofing.

--
Chris Green
  #20   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In article , writes

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.


This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so

But what's the point then?


That the lamp is not the problem and doesn't need cooling as it's
designed to run in a confined space BUT if its totally encapsulated in
rockwool then this combination may get hot enough to cause a problem to
nearby joists, boarding, whatever, so all the pot does is keep the
insulation away from the lamp and as air circulation around the lamp is
not a problem as its designed to go into a confined space you might as
well seal up around the edge of the pot to stop draughts from the
ceiling space into the room below and vise versa, whew

The insulation won't care either way as it's decidedly not
inflammable.

The one thing it *might* do is protect adjacent joists from the heat of
the lamp but I'm not all that convinced that "no flowerpot" will make
the joist any warmer than "flowerpot" will.

The idea of a 'chimney' of some sort (i.e. a largeish tin with both
ends cut off) seema a much more sensible approach to me.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this


You are probably also doing something awful to the fire proofing.

fire proofing???

--
David


  #22   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

wrote:
In article ,
writes

The lamp will probably run hotter as it's in a very enclosed space
with no ventilation.

This is what I was trying to say in my first reply, does it matter if it
runs hotter in an enclosed space? I don't think so

But what's the point then?


That the lamp is not the problem and doesn't need cooling as it's
designed to run in a confined space BUT if its totally encapsulated in
rockwool then this combination may get hot enough to cause a problem to
nearby joists, boarding, whatever, so all the pot does is keep the
insulation away from the lamp and as air circulation around the lamp is
not a problem as its designed to go into a confined space you might as
well seal up around the edge of the pot to stop draughts from the
ceiling space into the room below and vise versa, whew

I'm entirely unconvinced that the flower pot makes any difference
then. The lamp outputs the same amount of heat whatever you put
around it. This heat must escape to the surroundings which will thus
get just as hot whether you put a flower pot over it or not. In fact
it may produce hotter hotspots simply because you have reduced the
airflow somewhat.

The only gain *might* be that more of the heat goes down into the room
below but I'm not all that convinced that this will happen.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this


You are probably also doing something awful to the fire proofing.

fire proofing???

I meant that the hole in the ceiling, unless dealt with somehow,
reduces the fire barrier created by a plasterboard ceiling.

--
Chris Green
  #23   Report Post  
David
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool


wrote in message ...
wrote:

I can't say that I have noted the effect in low voltage lamps -
they are largely disposed to early failure anyway - though gls and
reflector lamps exhibit the same tendency...


I have mine enclosed in upturned pots and can't say that mine fail any
earlier than anybody else's

... but why have you got them in upturned pots? If it doesn't make
them run cooler what's it doing for the lamps or anything else?


It does nothing for the lamps,other than keep the insulation at bay.
the only way to make them run cooler would be to attach heatsinks to them,
or have some forced air cooling but that is totally unecccessary.

by having upturned pots around them you

1. prevent the insulation coming into direct contact with the lamp
2. have a convenient hole in the base of the pot to take the lead out of and
so keep the wiring on top of the insulation
3. have a cover which can potentially be sealed to minimise warm humid air
entering the loft space.

yes the pots will heat up.

without pots : the lamp heats up , then this heats the air. (assuming loft
insulation still held back)

with pots: lamp heats up, this heats up the air, the air heats up the pots,
the pots get warm and warm up the surrounding air in the loft.

There may be a slight increase in the lamp[ temperature over scenario 1 but
I didn't notice any after installing the pots, however before I put them
over our fittings I certainly did notice some condensation in the loft after
installing 4 spots in the ceiling. **

Since using the pots over the spots this has not been evident, an extractor
fan was also added at a later date.

** the spots were installed in mid january , and the conditions in the loft
checked a couple of days later, after fairly heavy use of the bath and
shower. the extractor fan had not been wired up at this point which would
obviously affect the situation as well.

regards

David



regards

David


  #24   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In article , writes
I'm entirely unconvinced that the flower pot makes any difference
then. The lamp outputs the same amount of heat whatever you put
around it. This heat must escape to the surroundings which will thus
get just as hot whether you put a flower pot over it or not. In fact
it may produce hotter hotspots simply because you have reduced the
airflow somewhat.


Chris, the lamp does not need airflow to keep it cool, that's the point
The pot keeps the insulation away (and creates a larger heatsink if you
really think that's necessary) but still maintains a sealed ceiling. I
have felt my pots on many occasions (ooer missus) and even after
prolonged use they are only warm to the touch as opposed to the bloody
hot that the lamps themselves get


The only gain *might* be that more of the heat goes down into the room
below but I'm not all that convinced that this will happen.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this

You are probably also doing something awful to the fire proofing.

fire proofing???

I meant that the hole in the ceiling, unless dealt with somehow,
reduces the fire barrier created by a plasterboard ceiling.

So the open tube/chimney idea makes this worse as it gives a path for
the flames as opposed to the sealed pot
--
David
  #25   Report Post  
mark
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

In message ,
writes
You are probably also doing something awful to the fire proofing.

fire proofing???

I meant that the hole in the ceiling, unless dealt with somehow,
reduces the fire barrier created by a plasterboard ceiling.

So the open tube/chimney idea makes this worse as it gives a path for
the flames as opposed to the sealed pot


As a builder this point has worried me for some time.
Everyone seems to want down lighters in their new houses/extensions.
Installed in floor void they make holes in the half hour fire protection
(plasterboard) and I have been told that a study (not seen it) claimed
that the blow lamp effect through the holes might actually accelerate
the destruction of the floor structure. For this reason I have been
making boxes around the down lighters from a fireproof board sealed up
with intumescent mastic; so far so good.

In a loft space they make holes in the insulation and make a mockery of
the regulations brought in regarding cold bridging through timber
joists. For this reason we have been making plasterboard boxes to give a
foot square space around the fitting to allow the heat to dissipate
while putting insulation over the box to complete the necessary
insulation requirement.
I am aware that the insulation probably mucks up the heat dissipation
but again; so far so good.

Foot square box; too small? I've been asked to install them in much
smaller available spaces between floor joists so I don't know...
I'd be very interested in other peoples comments and experiences as I
was on the verge of refusing to install them for all the above reasons
and I was worried about being sued


--
mark


  #26   Report Post  
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

wrote:
In article ,
writes
I'm entirely unconvinced that the flower pot makes any difference
then. The lamp outputs the same amount of heat whatever you put
around it. This heat must escape to the surroundings which will thus
get just as hot whether you put a flower pot over it or not. In fact
it may produce hotter hotspots simply because you have reduced the
airflow somewhat.


Chris, the lamp does not need airflow to keep it cool, that's the point


I never suggested it did, it was the OP asked the question "Preventing
halogen lights overheating under Rockwool". Lots of people answered
saying "put your lamps under a flowerpot". You agree totally with me,
putting a flowerpot over the lamp "won't" keep it any cooler.

Whether one needs to keep the lamp cooler is another matter
altogether.


The pot keeps the insulation away (and creates a larger heatsink if you
really think that's necessary) but still maintains a sealed ceiling. I
have felt my pots on many occasions (ooer missus) and even after
prolonged use they are only warm to the touch as opposed to the bloody
hot that the lamps themselves get

Since nothing except mineral wool insulation will touch the lamp if
the flower pot isn't there it doesn't really matter does it.


The only gain *might* be that more of the heat goes down into the room
below but I'm not all that convinced that this will happen.

If you are into insulation and draught proofing though, you have created
a hole in your ceiling unless you use the sealed lens type units, by
putting a pot over and sealing around the edge you prevent this

You are probably also doing something awful to the fire proofing.

fire proofing???

I meant that the hole in the ceiling, unless dealt with somehow,
reduces the fire barrier created by a plasterboard ceiling.

So the open tube/chimney idea makes this worse as it gives a path for
the flames as opposed to the sealed pot


Yes, absolutely. We're mostly in agreement you know! :-)

I'm just questioning whether/what the flowerpot does for you as
opposed to nothing.

I think it may well improve the 'fireproofness' of the ceiling if you
have a flowerpot over the lamp but I'm not totally convinced, it's
hardly well tested. Other than that I can see no point whatsoever in
putting the flowerpot there except that it makes things look tidier
(nothing wrong with that either).

--
Chris Green
  #28   Report Post  
Pete C
 
Posts: n/a
Default Preventing halogen lights overheating under Rockwool

On Tue, 29 Jun 2004 18:31:52 +0100, mark
wrote:

Foot square box; too small? I've been asked to install them in much
smaller available spaces between floor joists so I don't know...
I'd be very interested in other peoples comments and experiences as I
was on the verge of refusing to install them for all the above reasons
and I was worried about being sued


Hi,

Anyone tried measuring the temperature around the fitting with a
remote thermometer?

cheers,
Pete.
  #31   Report Post  
 
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David wrote:

putting a pot over it and preventing insulation coming into direct

contact
will obviously keep it much cooler than if the insualtion was in direct
contact with the lamp. That is the primary goal in doing it.

Now that I disagree with, I don't believe the flowerpot will keep the
lamp cooler. How does it do that? With a flowerpot over the lamp
there will be *less* air circulation than without, how is that going
to keep the lamp cooler?

The flowerpot may make things tidier and/or more fireproof but I really
don't believe it will keep the lamp cooler.

--
Chris Green


If you compare a lamp with insulation over it and one with a pot over it and
eth insualtion held back 10-15 cm then the one with the pot will be cooler
in comaprison.

Have you measured that? I really don't see how this can be true, do
you have any explanation as to why it should be cooler? There is
absolutely nowhere additional for the heat to go in the case where the
lamp is in a flowerpot so how can it be cooler?

--
Chris Green
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David
 
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wrote in message ...
David wrote:

putting a pot over it and preventing insulation coming into direct

contact
will obviously keep it much cooler than if the insualtion was in

direct
contact with the lamp. That is the primary goal in doing it.

Now that I disagree with, I don't believe the flowerpot will keep the
lamp cooler. How does it do that? With a flowerpot over the lamp
there will be *less* air circulation than without, how is that going
to keep the lamp cooler?

The flowerpot may make things tidier and/or more fireproof but I

really
don't believe it will keep the lamp cooler.

--
Chris Green


If you compare a lamp with insulation over it and one with a pot over it

and
eth insualtion held back 10-15 cm then the one with the pot will be

cooler
in comaprison.

Have you measured that? I really don't see how this can be true, do
you have any explanation as to why it should be cooler? There is
absolutely nowhere additional for the heat to go in the case where the
lamp is in a flowerpot so how can it be cooler?

--
Chris Green


The lamp will warm up the air around it and the warm air will rise.

As the warm air rises up it comes into contact with flower pot and the
flower pot then heats up.

the flower pot now gets warm and warms the air around it.

and so some heat from around the lamp is removed

Have i measured this with lamps. No I've no desire or need to do so.

I have looked the heatsinking requirements and thermal characteristics of
semiconductors? yes on quite a few occasions.

Lets say I have a component that must dissipate a fair amount of power, a
few watts say. Now if this just sits on a PCB board it gets pretty hot, the
internal temp may easily be about 125C, If I tightly pack other components
around it (i.e provide some insualtion) then it heats up to 175C and fails.
If on the other hand I add some heatsinking then its operating temp will be
much lower.

If you surround anything in insulation then obviously it will retain more
heat than if there is any sort of air gap.

Given that this is the whole point of the insulation it's something that
just seems common sense, I can't really fathom your problem with it. You do
not need to have an massive air flow to get heat transfered. As above you
will have heat transfered from lamp to air to pot to air. Not the most
effiecient heatsink in the world but when compared to 150mm of rockwool
there will be a difference.

regards

David


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Chris, David -

neither of you seem to have bothered stating what you're assuming happens
*around* the flowerpot. And it seems from the side as if one of you thinks
it's "totally obvious" that the flowerpot is *instead* of the rockwool,
i.e. that the top and sides of the inverted flowerpot are open to the
surrounding air - in which case the lamp will indeed run a lot cooler, since
the pot itself will be able to dissipate a fair proportion of the heat
produced by the lamp to the free air around it by both radiation and
convection. The other of you seems to assume the pot is covered/surrounded
by the rockwool, and under this assumption quite correctly points out that
once the air around the lamp and the pot have risen to pretty much the
temperature of the lamp fitting (which they will, since the surorunding
rockwool prevents nearly all the heat from going anywhere useful), the
temperature of the lamp under the pot under the rockwool will be no
different from the temperature of the lamp directly under rockwool.

Have I got the source of the divergent views right? (And will I regret
piping up at all? ;-)

Stefek
  #35   Report Post  
David
 
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wrote in message
...
Chris, David -

neither of you seem to have bothered stating what you're assuming happens
*around* the flowerpot. And it seems from the side as if one of you thinks
it's "totally obvious" that the flowerpot is *instead* of the rockwool,
i.e. that the top and sides of the inverted flowerpot are open to the
surrounding air - in which case the lamp will indeed run a lot cooler,

since
the pot itself will be able to dissipate a fair proportion of the heat
produced by the lamp to the free air around it by both radiation and
convection. The other of you seems to assume the pot is covered/surrounded
by the rockwool, and under this assumption quite correctly points out that
once the air around the lamp and the pot have risen to pretty much the
temperature of the lamp fitting (which they will, since the surorunding
rockwool prevents nearly all the heat from going anywhere useful), the
temperature of the lamp under the pot under the rockwool will be no
different from the temperature of the lamp directly under rockwool.

Have I got the source of the divergent views right? (And will I regret
piping up at all? ;-)

Stefek


well I'm half way in between

the pot is in a hole in the insualtion but the top is not covered with
insulation.

cheers

David




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In uk.d-i-y, David wrote:

the pot is in a hole in the insualtion but the top is not covered with
insulation.

Then you'll get radiation losses from the top of the pot, but not much
in the way of convection, since there's not much chance of air getting
to the bottom of the pot to start an updraught. An old lath-n-plaster
ceiling will provide more in the way of airgaps for convection than a
nice new plasterboarded one - to get convection going there you'd want
to stand the pot on some spacers, or nibble some gaps into the rim (as
if the little bleeders won't crack if you try ;-)

Stefek
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David
 
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wrote in message
...
In uk.d-i-y, David wrote:

the pot is in a hole in the insualtion but the top is not covered with
insulation.

Then you'll get radiation losses from the top of the pot, but not much
in the way of convection, since there's not much chance of air getting
to the bottom of the pot to start an updraught. An old lath-n-plaster
ceiling will provide more in the way of airgaps for convection than a
nice new plasterboarded one - to get convection going there you'd want
to stand the pot on some spacers, or nibble some gaps into the rim (as
if the little bleeders won't crack if you try ;-)

Stefek


Exactly, as long as you have some exposed surfaces you will have losses.

I'm not too sure about your radiative/convective loss assessment though.

Given that the top of the pot is pretty much sealed it doesn't matter if you
get any air down at the bottom of the pot, by whatever means

As the loft space is going to be considerably colder than the pot, (it is
well insulated after all), and there should be decnt ventilation, then there
will be a reasonable air flow above the pot. So most of the heat may well
be removed from the top of the pot by convection.

cheers

David


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In uk.d-i-y, David wrote:

I'm not too sure about your radiative/convective loss assessment though.

Given that the top of the pot is pretty much sealed it doesn't matter if you
get any air down at the bottom of the pot, by whatever means

Ah, sorry, there's another unstated assumption of mine - that the pot has
a Hole in the middle of the "base" (base when used as pot, top when used
as light cover) - 'cuz all the pottery pots I've seen have this kind of a
drainage hole in them. Thuz, the conditions are right for a useful
convective flow from the bottom of the pot to the top, if air can get
in at the bottom. If there's no such 'ole, then of course there isn't
going to be nearly the same air flow, and a higher proportion of the
(smaller) losses will be by radiation (assert): though you're right that a
fair bit of the losses even from an "unholed" pot will be from convection
currents around the outer surface of the pot.

(Have we worked this one to death yet? ;-)

Stefek
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David
 
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wrote in message
...
In uk.d-i-y, David wrote:

I'm not too sure about your radiative/convective loss assessment though.

Given that the top of the pot is pretty much sealed it doesn't matter if

you
get any air down at the bottom of the pot, by whatever means

Ah, sorry, there's another unstated assumption of mine - that the pot has
a Hole in the middle of the "base" (base when used as pot, top when used
as light cover) - 'cuz all the pottery pots I've seen have this kind of a
drainage hole in them. Thuz, the conditions are right for a useful
convective flow from the bottom of the pot to the top, if air can get
in at the bottom. If there's no such 'ole, then of course there isn't
going to be nearly the same air flow, and a higher proportion of the
(smaller) losses will be by radiation (assert): though you're right that a
fair bit of the losses even from an "unholed" pot will be from convection
currents around the outer surface of the pot.

(Have we worked this one to death yet? ;-)


Is that not the whole point of a decent thread on usenet? :-) There is
always another avenue that you can veer off down if you really desire, but
whether anyone else follows is another matter.

This thread could just be in its infancy compared with an Andy Hall/IMM
tit for tat match :-)

cheers

David



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