Chimney breast temperature.

[Selfmade]

I'm trying to find out the likely maximum tempertaure that will occur on a chimney breast so I can work out what type and size of cable to use for a socket, and whether I need to move some existing cables. The chimney is granite with a clay liner and will be serving a multi-fuel stove with a flexible metal liner within the clay. The chimney breast is lined with lath and plaster and I'm hoping to run the cable behind this, just above the fireplace. The existing cables are 2.5mm2 PVC flat twin and earth forming part of the ring final. These drop down from the loft and cross the path of the chimney, probably on or two meters up.

P.S. I've looked on some stove/chimney type fora and they just talk about 'warm', 'hot', 'very hot' etc. - not so precise as us lot!

 

[telectrix]

bang some MICC in. that should do the trick.

 

[Selfmade]

bang some MICC in. that should do the trick.

Great suggestion, thanks, but horribly expensive - like £50 just for the cable to get round the fireplace. I don't want to spend that unless I can't avoid it! (Own home so no-one to pass the cost onto.)

 

[Squid]

Great suggestion, thanks, but horribly expensive - like £50 just for the cable to get round the fireplace. I don't want to spend that unless I can't avoid it! (Own home so no-one to pass the cost onto.)

Better safe then sorry, £50 isn't that much in the scheme of things.

 

[LankyWill]

Whats £50 for the sake of a reliable solution, quit being a cheapskate and enter the realm of reality. A bit of Twin isnt going to last 5 minutes...

 

[Selfmade]

Absolutely agree! If it needs it that is what I'll fit. I just didn't want to spend that if the chimney breast would be like 50C max and fine with some heat resistant flex. Looks like I'll be replacing the ring cables with MICC as well then.

 

[Squid]

If you are self employed then off set the cost against your tax bill.

 

[Selfmade]

If you are self employed then off set the cost against your tax bill.

Would I do that?

 

[Squid]

Would I do that?

I was in IT as Limited Company and one year I claimed for the Christmas Tree as an expense and the accountant passed it, why not get what you can if its legal and passes your accountants beady eyes. A lot of people don't claim for what can be claimed.

 

[Richard Burns]

The outer layer of a chimney breast will not get above 60°C because otherwise you would burn yourself on the wall and this does not happen.
The actual vent from the mulitfuel stove will get very hot but this heat will be limited by the metal liner that will also provide some heat dispersion. Then you will have the clay and granite (really!) insulating the cable from the heat.
You could almost certainly say that the ambient temperature of the cable could be in the region of 40-50°C and take that into account. Obviously twin and earth cable would have its life reduced in this heat but probably only by a few years. A slightly cheaper alternative to MICC would be silicone cable that is suitable for, I think about 200°C; I would probably put 4mm² twin and earth in an easily accessible conduit across the front of the chimney, then it could be readily replaced if there is deterioration.

 

[Selfmade]

I was in IT as Limited Company and one year I claimed for the Christmas Tree as an expense and the accountant passed it, why not get what you can if its legal and passes your accountants beady eyes. A lot of people don't claim for what can be claimed.

Well I guess if the lounge is also my office (which it probably will be in the winter with this stove!)...

 

[Selfmade]

The outer layer of a chimney breast will not get above 60°C because otherwise you would burn yourself on the wall and this does not happen.
The actual vent from the mulitfuel stove will get very hot but this heat will be limited by the metal liner that will also provide some heat dispersion. Then you will have the clay and granite (really!) insulating the cable from the heat.
You could almost certainly say that the ambient temperature of the cable could be in the region of 40-50°C and take that into account. Obviously twin and earth cable would have its life reduced in this heat but probably only by a few years. A slightly cheaper alternative to MICC would be silicone cable that is suitable for, I think about 200°C; I would probably put 4mm² twin and earth in an easily accessible conduit across the front of the chimney, then it could be readily replaced if there is deterioration.

Kind of what I expected (and hoped). I grew up with stoves and open fires and remember the walls getting warm but never really hot. I'll look into the silicone. But I suspect HR flex and the T & E will be fine at these temperatures (I'll do my calcs of course). The existing T & E should be easy enough to replase if the need arrises and I seem to be constantly making minor alterations to this place so unlikely the ring final will go more than a year or two without an IR test!

I don't find the granite that good an insulator to be honest, but I'm pretty sure it will conduct far more heat outside than into the room .

 

[PEG]

Hi dude,are you sure it is lined with lath and plaster?

If it is constructed correctly,from original,any timber should not be getting up to any temperature a cable would not be comfortable with.

Me folks have a sizeable Dunsley Yorkshire stove,with an unlined 9" brick chimney,and in winter,the breast will be warm,right through the bedroom.

But no warmer than the brickwork,behind any radiator.

 

[robd]

I agree with Richard.

 

[Selfmade]

Hi dude,are you sure it is lined with lath and plaster?

If it is constructed correctly,from original,any timber should not be getting up to any temperature a cable would not be comfortable with.

Definitely lath and plaster: The fireplace was boarded up with plasterboard. I have unboarded it right back to the original lath and plaster which I can see and feel, especially where the plaster has crumbled away from in front of the lath. I'm sure the cables would not be damage by the heat at this point as you say - the wood has been there a long time and shows no sign of scorching. But the cables will be derated above 30C. However I have now checked the tables and they should be alright.

Me folks have a sizeable Dunsley Yorkshire stove,with an unlined 9" brick chimney,and in winter,the breast will be warm,right through the bedroom.

But no warmer than the brickwork,behind any radiator.

Good to get further confirmation, thanks