Replacing log burner

[Bogart]

I would like to replace a log burner by an open grate. Currently the log burner flue passes through a steel plate the size of the firelpace area then enters an insulated steel liner then up to the outside world.
What I am not to sure on is how the get the grate smoke up the stack. Would I remove the liner? I thought not as condition of stack brickwork unknown. Do I need some sort of canopy to funnel the smoke up the stack?
Additionally the logburner just rests on bricks on their sides with no mortar between. With hot ash inevitably going to end up on these bricks should they be cemented in or do I possible need different bricks totally?

 

[88v8]

Mmmm, picture?

Age of flue?

It may indeed be that the log burner and liner were introduced because the parging has failed. In that case, going back to an open fire will be difficult to say the least.

Speaking as someone who went from open dog grate in inglenook, to log burner, the latter is much easier to light and chucks out far more heat. And doesn't smoke. One can run logburners with the doors open once they are well alight, if one wishes.

Is there a sweeping hatch in the register plate? If so, you can poke some smoke bombs through it, the sort used in smoking greenhouses, set them alight by a linked fuse of string soaked in petrol, then close the sweeping eye and nip upstairs and see whether any smoke is coming into the bedrooms or attic. If not, the parging is likely OK, but it would be worth getting a second opinion before committing to remove the liner.

If you were to keep the liner in there, to avoid possible parging problems, that would greatly restrict the size of fire opening you could have without it smoking back into the room.
There is a ratio between fire opening and flue cross-section, ideally in the range of six, and not more than eight otherwise it will tend to fill the room with smoke, worse some days than others. If you left a (six inch?) liner in there, that limits the fire opening to a foot square !! A dolls' house forsooth.
So for an open fire, you would really need to remove the existing register plate.

However, if this is an inglenook and you don't want all your heat rushing out, you could put in another register plate with a fire hood, that would reduce the size of the opening.

Inglenooks often smoke due to excessive cross-section &/or inadequate ventilation into the room. You will doubtless recall related topics on here. A hood also helps minimise smoking as it reduces the effective cross-section of the fire opening.

Some preliminary thoughts.........

Ivor

 

[Bogart]

Thank you for the detailed reply. The flue is around 5 yrs old and was inspected a few months ago by the insurance people. Both the inside of the liner and inside of the chimney itself were found to be in a satisfactory condition. An endoscope camera was sent up the liner and the chimney out to the top of the stack, so I am reasonabley confident the chimney is in a useable condition. There is no access through the register plate but I am sure one could be sorted and then I could use some smoke bombs up there. The log burner was only installed as the previous owner "liked" them. We have an unlimited supply of wood so I thought a big grate would counteract to some degree the heat escaping and allow a reasonable amount into the room. You have suggested though that the liner may need to come out. If memory serves me I think the liner is quite large but I can check as I have an endoscope camera and can have a look myself through a small hole which was drilled in the register plate for the insurance man to access it. I was thinking of some type of hood hidden up out of view, though if the register plate and liner come out there is no need.

 

[88v8]

Interesting.
Five years old... I take it you mean the liner rather than the flue. Insurance... thatched? So the house is pretty old. And the flue not particularly sophisticated, no kicks, lie on your back in the fireplace and you can see the sky....? Like ours.......

We had our liner checked with a camera, but not the flue as I have no intention of going back to an open fire.
The other issues with our open flue, which is about 12" square at the top, the heat of course rushed out, and because it has no kick the rain came in, so much so that the thick firebars had rusted through due to water falling on the ash residue.
The fire opening was not that large, about 4 x 4ft, but judging by the smoke stains on the fire arch it used to smoke and the PO had installed a hood. Nevertheless it was a pig to light.

How much heat you get from your open grate depends on how well it draws, and how well it reflects heat into the room. A dog grate with an iron fireback won't be terribly effective and will eat fuel. But if it's more for period atmosphere than necessary heat, that doesn't really matter. We need our woodburners, in the evening they are our primary heat source.

And if after a while you don't like your open grate, you can always reinstate the woodburner. It's only money.

Ivor