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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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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
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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
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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
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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 |
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Preventing halogen lights overheating under Rockwool
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#6
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Preventing halogen lights overheating under Rockwool
Or you could cut lengths of 100mm diameter aluminium ducting hose. |
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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 |
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Preventing halogen lights overheating under Rockwool
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#9
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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. |
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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 |
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Preventing halogen lights overheating under Rockwool
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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 |
#14
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Preventing halogen lights overheating under Rockwool
wrote in message ... 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? It is keeping an air space around the lamp and the insulation away from the lamp too. |
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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 |
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Preventing halogen lights overheating under Rockwool
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#17
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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
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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
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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 |
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Preventing halogen lights overheating under Rockwool
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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 |
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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 |
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Preventing halogen lights overheating under Rockwool
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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 |
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Preventing halogen lights overheating under Rockwool
wrote in message ... wrote: In article , writes 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. But Chris 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. regards David |
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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. |
#29
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Preventing halogen lights overheating under Rockwool
David wrote:
wrote in message ... wrote: In article , writes 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. But Chris 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 |
#30
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Preventing halogen lights overheating under Rockwool
wrote in message ... David wrote: wrote in message ... wrote: In article , writes 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. But Chris 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. regards David |
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Preventing halogen lights overheating under Rockwool
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 |
#32
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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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 |
#34
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Preventing halogen lights overheating under Rockwool
wrote:
Have I got the source of the divergent views right? (And will I regret piping up at all? ;-) While we are at it, we've not even touched on transformers, a typical spec for which says not to put under insulation. Presumably they will have to be screwed onto the roof framing well above the joists and all the layers of Rockwool? Chris -- Chris J Dixon Nottingham UK Have dancing shoes, will ceilidh. |
#35
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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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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Preventing halogen lights overheating under Rockwool
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