fitting pot and cowl to old chimney and hearth

Ronnie_Rotten

A neighbour asked me to close the chimney down to clay pipe size so he can fit a cowl to stop the rain coming in. The fireplace is the original wide cottage style with all the iron works. He doesn't want to alter any of that.
I put steel plate accross the top of the hole, rested the pot on top and cemented it in. He lit a fire in there yesterday and the place filled with smoke. I'm not convinced he lit a proper fire, like one where the heat had built up enough to make the smoke rise properly.
Because we used the edge of the chimney to support one side of the clay pipe, he is convinced that if we move the pot more to the middle it will magically cure the problem. I don't see it making any difference. If the smoke has travelled 25' up, it won't mind moving 8'' to the side!

So.... does a large open hearth NEED a large opening at the top of the chimney (it was 17''x19'') , or will a clay pipe be sufficient provided there's a hot fire lit?

Robbie.G

Ronnie_Rotten wrote: »

A neighbour asked me to close the chimney down to clay pipe size so he can fit a cowl to stop the rain coming in. The fireplace is the original wide cottage style with all the iron works. He doesn't want to alter any of that.
I put steel plate accross the top of the hole, rested the pot on top and cemented it in. He lit a fire in there yesterday and the place filled with smoke. I'm not convinced he lit a proper fire, like one where the heat had built up enough to make the smoke rise properly.
Because we used the edge of the chimney to support one side of the clay pipe, he is convinced that if we move the pot more to the middle it will magically cure the problem. I don't see it making any difference. If the smoke has travelled 25' up, it won't mind moving 8'' to the side!

So.... does a large open hearth NEED a large opening at the top of the chimney (it was 17''x19'') , or will a clay pipe be sufficient provided there's a hot fire lit?

Did the fire work before you did this work.By putting a flue pot on it it shouldn't have any bearing on it unless you blocked most of the flue.

Ronnie_Rotten

It's a holiday cottage owned by a couple of americans who come occasionally in the summer months, the neighbour just keeps the grass down, and generally keeps the place for them. I have to assume the fire has worked as it was for a couple of hundred years or so!
Yes, by putting the pot on top, the flue at the very top of the chimney has reduced from 19''x17'' to a far smaller 10'' diameter circular chimney pot. Below this and for the entire length of the chimney nothing has changed.

It's either a case of 'this hearth needs a big chimney flue because of it's size, style etc.' Or 'it should be fine because... blah blah etc'

I'm sure there's a calculation pertaining to size of hearth, heat of fire, size of chimney. Even it's just a rule of thumb.

I did wonder when he said 'put this up there' if he knew what he was on about. I wondered even more when he said 'move the pot 8''. That'll fix it'

Robbie.G

Ronnie_Rotten wrote: »

It's a holiday cottage owned by a couple of americans who come occasionally in the summer months, the neighbour just keeps the grass down, and generally keeps the place for them. I have to assume the fire has worked as it was for a couple of hundred years or so!
Yes, by putting the pot on top, the flue at the very top of the chimney has reduced from 19''x17'' to a far smaller 10'' diameter circular chimney pot. Below this and for the entire length of the chimney nothing has changed.

It's either a case of 'this hearth needs a big chimney flue because of it's size, style etc.' Or 'it should be fine because... blah blah etc'

I'm sure there's a calculation pertaining to size of hearth, heat of fire, size of chimney. Even it's just a rule of thumb.

I did wonder when he said 'put this up there' if he knew what he was on about. I wondered even more when he said 'move the pot 8''. That'll fix it'

What vent is in the room? Is there anything that has changed inside house new windows/doors /extract fans.When the fires lit if you open a window or door does it make a difference.How high is the chimney,is the chimney sound and not leaking smoke.They are some of the things that can cause the problems your having.I would think the problem is air supply

Ronnie_Rotten

Now i havn't been in to light a fire myself. The neighbour did, and then got smoked out.

From my research....

The internal surface should be smooth, not a jagged cheese grater affair (which is what we have)

If the fire is lit too low, the gasses are too cold by the time they hit the flue and there's no updraught (i suspect this happened)

The termial (pot or otherwise) at the top of the chimney should be equal in size to the flue for an open fire application (not any more it's not!)

A dovecote cap is better suited to wide old chimneys if youmdon't want to mess with flue liners etc.

So. I think i'll light a proper fire and see where i get with it. I supect i'll be climbing onto a thatch roof with a paving slab and 4 blocks to build a dovecote though. I'll have to charge for that...

Robbie.G

Ronnie_Rotten wrote: »

Now i havn't been in to light a fire myself. The neighbour did, and then got smoked out.

From my research....

The internal surface should be smooth, not a jagged cheese grater affair (which is what we have)

If the fire is lit too low, the gasses are too cold by the time they hit the flue and there's no updraught (i suspect this happened)

The termial (pot or otherwise) at the top of the chimney should be equal in size to the flue for an open fire application (not any more it's not!)

A dovecote cap is better suited to wide old chimneys if youmdon't want to mess with flue liners etc.

So. I think i'll light a proper fire and see where i get with it. I supect i'll be climbing onto a thatch roof with a paving slab and 4 blocks to build a dovecote though. I'll have to charge for that...

The whole chimney is wrong but it worked previously.Air flow to fire is important.The flue gases could be cooling to quickly not allowing it to draw even with the smaller pot it should still draw.But to cover yourself considering its a thatch with a problem chimney I'd be very careful with anything I would do
There's info here that may help
http://www.soliftec.com/thatch.htm

DenisCork

Hi Ronnie,

large open fireplaces do need larger flues, the bigger the fireplace op the bigger the flue. They also need a lot of ventilation into the room. There's info here on larger fireplaces.