How strict are HETAS when installing a stove?

[dominoman]

I would like to install a woodburner stove in my lounge. There is a deep hearth there (6 feet of brick and concrete!) which extends 10 cm each side of the opening and 35 cm out.

I would like to add a thick limestone slab hearth on top and I have one that fits exactly and would look great.

The limestone slab would extend 400mm from the front of the opening. Building regs state it must be 500mm now.

Will the HETAS stove installer insist it needs to be larger? How strict are they on this type of thing? I know it is totally safe (and in fact the small stove I'm getting doesn't even require a constructional hearth as it has bottom heat shields).

I just dont want to install the hearth and then have to remove it all. Is that likely?

 

[dominoman]

Just to add - originally this was an open fire, and it is an Edwardian house. The new hearth would be larger and wider than the original one built with the house.

 

[Tipper]

I suspect you won't get a HETAS certificate of compliance with Building Regs if it doesn't!

 

[SFK]

Domionman,
I think you need to speak to you Hettas installer as it would be best to see what he says as he is likely to give better guidance (as he is the one who will signoff) and be more satisfied that you are meeting regs if you dicussi it with him.

But my reading (which I am happy to be shot down on if I am wrong) of the Hettas guide at
http://www.stovefittersmanual.co.uk/articles/hearth-regulations/
is that the "constructional hearth" which is the concrete below your fire and limestone slab hearth should extend 50cm out and Your limestone "superimposed hearth" then sits on top of the constructional hearth and Your limestone "superimposed hearth" should extend more than 22.5cm out (not 50cm) from the door of the door of your log burner.
So, your Your limestone "superimposed hearth" is okay, but can you extend your "constructional hearth" by 35cm to 50cm? (<< my reading of this, is that the constructional hearth section lies under the floorboards and carpet.
sfk

 

[dominoman]

Thanks SFK. Reading it again I think you are right. I had always assumed the superimposed hearth would have to cover at least the size of the constructional hearth, but the second diagram on that link shows it as smaller.

In fact my constructional hearth does extend out 50cm, but part of that is under the floorboards. Sounds like I will be OK.

Thanks again.

 

[chappers]

The required hearth can't be below the floorboards, the measurements are from the front of the door to the nearest combustible material, eg carpet wooden flooring etc
This should be 225mm for a fire that is primarily designed to be operated with the door closed or 300mm for an open fire or one that can operate with the doors open.

 

[SFK]

Chappers,
My reading of the specs is that it is the "superimposed hearth" (which is DomninoMans Limestone hearth) has to extend more than 225mm for a fire that is primarily designed to be operated with the door closed or 300mm for an open fire. So I think your message (and what I was trying to explain) is that he is therefore okay as his Limestone superimposed hearth extends by 350mm.

But there is also a spec for a "constructional hearth" that extends out 500mm and this is the lump that is under the "superimposed hearth" and extends beyond it and under the floorboards/carpet.

DomninoMans, in respnse to your question why does the the "constructional hearth" extend under and then beyond the "superimposed hearth", in my house this is what the floor joists are attached to (and end at) and I always supposed that this specification was to stop the Joists ending up under or near the "superimposed hearth" and perhaps catching fire

here is a link to blacken and charred joists that were found under the "superimposed hearth" when the fire was was opened up for installation of a new fireplace:

//www.diynot.com/diy/threads/burning-under-hearth.442141/#post-3461296

SFK

 

[chappers]

I have never known of a fitter insisting that the constructional hearth is extended. Have done work in plenty of houses where a woodburner has been fitted into an existing fireplace and we have always just covered the flat stone level hearth with a decorative hearth and these have usually been in the region of 350-400mm.

 

[dominoman]

Many thanks all for the advice and putting my mind at rest

I'm going to stick with the original constructional hearth (approx 500mm from fireplace front, of which only the last 100mm is under the recent floorboards) topped with a 1500 x 450 x 40mm slate slab.

That is all well within spec (based on SFK's interpretation of the regs, which I think is correct)