Mantle shelf over a recessed fireplace - how high?

[Tim Watts]

Hi,

OK - been through Part J building regs and I cannot find the answer.

How high above a fireplace opening should a combustible (wooden) mantle-shelf be?

The opening contains a coal burning stove, the front face of which sits flush with the brick opening. About 5kW max output give or take.

I've seen them quite low (12" above the top of the fire) but I'm looking for the right answer, rather than a dodgey example I've come across.

I'm not to bothered, looks wise - a high position would work quite well, so I do want to get it right :)

Cheers if anyone knows...

Tim

[Sailor]

Tim Watts wrote

Similar rules to shelving over a cooker ?

[Tim Watts]

Well, just managed to get hold of the BCO (not a given) and he could not find a definitive either, though he was sure it should be in Part J.

He agreed that >300mm would be considered dead safe.

OTOH here's an interesting doc from some USasian regs:

[JimK]

/ OTOH here's an interesting doc from some USasian regs:/q

Strewth they do enjoy prescriptions don't they!

Spose ultimately what's the "flash point"? of the mantel materials vs how hot could a fire/stove get it realistically.... Smoke & co alarms being in evidence (naturally) I would wonder how big the real risk is from something fixed up that "looked right".

On cold days one stands ones arse closer to fires than mantels....

Jim K

[Tim Watts]

I think you have to factor in people leaving overhanging papers (letters) and stuff on mantels.

My stove blasts heat out the front radiantly - and quite a lot rises up the front of the breast as hot air, but the air is hot, not scorching.

I've settled for 300mm from edge of opening to all combustible parts (actual mantel is in line with the yakee regs) - luckily that happens to be where it looks best too :)

I was also surprised that my chimney actually meets modern building regs. I thought the rear was half brick aka single thickness (to another room), Part J requires 200mm or more thickness.

Measured it and it is actually full brick and somewhat > 200mm.

[Martin Brown]

And they don't do "math" as they call it.

But not for many hours on end. The guy who installed mine said in no uncertain terms not to use polyurethane varnish on it as the wood can get warm enough to discolour or even melt varnishes at some distance.

Mine has a cunning geometry that puts a hidden piece of concrete between the line of sight from the stove to the mantle closest to the wall which shades most of the wood from the hot stove top surface.

Beeswax or Danish oil works fine.

I am incidentally moderately impressed with the stove Peltier fans which move warm air out of the old fireplace enclosure into the room.

[JimK]

ow hot could a fire/stove get it realistically.... Smoke & co alarms being in evidence (naturally) I would wonder how big the real risk is from someth ing fixed up that "looked right".

Depends on the temp differential.

did you test his theory? melting polyurethane sounds nasty and rather too h ot to me, if that usual, you'd think there'd be more than a "random install er comment" about the danger(s) of it...

mine have chimney breasts!

Jim K

[JimK]

ow hot could a fire/stove get it realistically.... Smoke & co alarms being in evidence (naturally) I would wonder how big the real risk is from someth ing fixed up that "looked right".

fahrenheit 451 :>) 232 odd deg C, think i'd be doing well if only the paper s went up!

indeed, its just been warmed from say 15-16 deg C at the floor and convecte d around, away & up from the cast iron lump. Whether things overhanging in that air flow could get to autoignition is the real question...

Goodo - the ancients probably learnt the hard way :>)

Jim K

[David]

Just a thought....

...I would have expected the information to be in the installation manual as the amount of heat chucked out and the direction must be fairly specific to the stove design.

I don't have our Stovax manual to hand, but I have vague memories of diagrams and stuff about clearances around the stove.

Cheers

Dave R

[Tim Watts]

Good point Dave - I have the PDF somewhere - I will try that...

[Dave Liquorice]

Peltier? Presumably you attach one side to the stove and cool the other some how to generate a power to drive the fan which helps cool the peltier? I've seen heat engine stove fans ones.

Ahhh...

If the cloud chamber can't be made to work the bits can be repurposed. B-)

[Vir Campestris]

There's _loads_ of stuff in our stove manual.

Andy