Lighting Dilema - (LV "air gap")

Floor's still up prior to UF and we have a dilema.

I'll re-explain the situation as it's been a while. Bedrooms/Bathroom downstairs, Lounge/dining/kitchen/hall Upstairs.

UFH going down in the whole of the upstairs living area.

Problem - Bathroom is currently illuminated with 4 x LV "eyeball" lamps set in ceiling. No problem so far, but UFH + Isulation etc will bring base level down by 3" in an 8" joist, plus, in order to reduce sound levels downstairs I am filling the void under the base ply with rockwool, which will reduce air circulation to very little.

So, question is, is a 5" space above a LV Halogen enough to prevent possible "heat" implications. If this is too close to the limits, what could anyone suggest as alternative lighting to put in the holes left by the LV lights.

Many thanks

Pete

Reply to
Pet
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Can't directly answer the question but a few thoughts spring to mind:

1: All the halogen downlighters I've installed recently (mains and LV) simply state a minimum clearance around the fitting. This seems to vary between fittings but is always in the 50mm to 150mm range (2" to about 6"). They say nothing about the airflow...

2: Having noted that, all the installation diagrams I've seen recently show the light installed in an "open" box - they are showing a typical situation with a floor above, ceiling below and joist to one side. They all have the fourth side "open" (and don't mention sides 5 & 6 :-)

3: An ordinary ceiling/floor void will probably be quite airy - plasterboard and wood are counted as "thermally conductive" for the purposes of cable sizing for example. Surrounding your fitting on 5 out of 6 sides with quite a lot of very good insulation, and not only that but heating the top (slightly, through the insulation) would, I would have thought, give potential for quite high temperatures in whatever cavity you arrange around the fittings. Whether or not this is detrimental to the bulb and bulb holder (probably not) this should certainly be taken into account when you consider the cable you use to attach the lamp to the transformer. Ordinary PVC is only rated to 70C and even "high temperature" PVC or rubber cable (as used on heaters for example) is only rated to 80C IIRC.

4: Speaking of the transformer, don't forget that this (these?) will also need ventillation.

As for possible alternatives... well, all incandescent lights produce copious amounts of heat... LEDs?

Hwyl!

M.

Reply to
Martin Angove

Many thanks for your pointers Martin, I have been looking at alternatives, possibly even just trying Mains Halogens, as at least there isn't a transformer adding to the heat build up..... then again, would it be technically incorrect to have 240V halogens above the bath I wonder?

I could also do away with some of the rock wool around the lights as it's only the bathroom so sound won't be such an issue, besides, 45mm cellotex with 15mm screed on top will already deaden the transfred sound somewhat.

Also bveen looking into LED lights, but have no idea whether a 9 LED unit would give enough light t replace the halogens.(one in each place)

Thanks again for taking time to respond.

Cheers Pete

Reply to
Pet

I would think that the bulk of the heat comes from the lamp itself rather than the transformer. Transformers tend to get "warm" in use, but would you attempt to touch a lit 50W halogen? Dichroic lamps are worse in this respect because the reflective coating is designed to allow the IR (heat) through to the back of the lamp whereas ordinary silver reflectors bounce a proportion of the heat forwards too.

It is possible to get both sorts in both 12V and mains versions, but be aware that some lamp holders are not specified for dichroic (also known as "cool beam") lamps, and the mains versions have a differently shaped ceramic base which means that although you can install a reflective lamp in a fitting designed for dichroic you can't the other way about.

It's perfectly allowable to have 240V fittings subject to certain restrictions :-) The thing to look out for is the "zone" in which you are installing the light and the minimum IP rating of fitting required for that zone. Oh yes, and if they are earthed fittings (many are not) they must also be part of the bathroom supplementary bonding.

If your ceiling is 2.25m high or lower then the part directly above the bath is zone 1. I don't have my copy of BS7671 or the OSG to hand but IIRC you can install 240V lighting in this area so long as it is protected to IPX4 *and* is supplied from a 30mA RCD.

If there is no over-bath shower then zone 2 starts immediately outside the bath and at a height of 2.25m above it. In zone 2 you still need an IPX4 fitting, but don't need the RCD.

This is something I really can't answer. Common sense says to me that clearing the Rockwool to leave a cuboid around the fitting of minimum dimensions (for example, 4") would leave a well-insulated cuboid within which the temperature could very easily reach well into three figures.

If your LV lighting transformer is installed in the same space as the downlighter (e.g. as is common with "through hole" transformers feeding just one lamp each) then check the transformer's Ta (ambient operating temperature; sometimes stamped on the device) This is unlikely to be higher than 50 or 60C.

I would be tempted to forget the Rockwool altogether above the bathroom, or at least only install it between joists where there is no downlighter fitted.

I've never used LED lights in this role. It is possible to get LED lamps which directly replace GU/GZ10 mains halogens but I would be very surprised if the light output was in any way comparable. There have been some lengthy LED/CFL/incandescent debates here within living memory, it might be worth your while looking one or two up.

Hwyl!

M.

Reply to
Martin Angove

not the remotest chance.

NT

Reply to
N. Thornton

[...]

Neglected to mention, of course, that it is also possible to get CFL lamps in GU10 format. These may be more acceptable than LEDs, subject to the debates I mentioned :-)

Hwyl!

M.

Reply to
Martin Angove

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