Chimney altered for stove, used for open fire?

[meanwhileinhell]

Hi all,

I hope this is the correct forum for this question.

I moved into a house a couple of years ago that had a wood burner in the living room. A new header was installed in the breast with just a hole in the middle for the flue, and then the piping/lining all the way up to the top (at least, that's what the previous owner told us, and that "...it would never need swept.").

Anyway, we recently removed the stove as it was dangerous, and we have got a case iron open fireplace as a replacement. However, when we lit it, there was a pretty poor draw, and some smoke coming back into the room.

What I want to know is, could this be because of the stove header/lining having an insufficient hole for this type of fire? If so, is there anything short of replacing the header and removing the lining, or installing a chimney fan, that we could do that would help the draw? Also, the chimney isn't capped (which is something I will be doing to all of them in time), and we may have a birds nest, but I just want to ascertain that the header isn't a problem before tackling this as the sole problem.

Thanks!

 

[Blagard]

While you removed a stove for being dangerous. It sounds as if you then went on to light a fire without ensuring the flue was suitable and safe.

Please take the alternate view and assume the whole lot is dangerous until you have checked and know it is suitable and safe.

Because there are so many unknowns in your post, I suggest you read through the BFCMA guide in the link below especially the sections on flue sizing, checking and testing. I appreciate it is primarily for people considering a stove, but the open fire situation seems covered to


http://www.stovesonline.co.uk/stove-chimney-documentation/bfcma-guide.html

 

[geraldthehamster]

What I want to know is, could this be because of the stove header/lining having an insufficient hole for this type of fire?

Do you mean that the register plate, that seals off the opening above the hearth, and that the stove pipe went through, is still in place? In that case, yes. But as said, have the whole chimney and flue checked.

Cheers
Richard

 

[meanwhileinhell]

Thanks for the replies.

@Blagard: Ok, that was probably my bad. We lit a smoke pellet to test the draw, not a full fire, as I was suspicious about there being an ample one for the open fire.

The reason we knew the stove was dangerous is when we came to redecorating. The white paint above our picture rail was discoloured indicating that the stove wasn't sealed correctly (however not enough set off the CO2/smoke alarm we had fitted). Closer inspection showed that there was a brick holding a plate against the back of it, which also explained why it burned so fast.

@geraldthehamster: We don't have a register plate, it is a concrete slab with a hole in it for the flue, that was sealed with fire cement. This slab seems to support the chimney also. I have attached a (rather crude) drawing of what it looks like.

Untitled

• meanwhileinhell
• 26 Nov 2013
• 1

[/img]

 

[geraldthehamster]

@geraldthehamster: We don't have a register plate, it is a concrete slab with a hole in it for the flue, that was sealed with fire cement. This slab seems to support the chimney also. I have attached a (rather crude) drawing of what it looks like.

Untitled

• meanwhileinhell
• 26 Nov 2013
• 1

[/img]

Is the concrete slab part of the original fireplace construction? What sort of fire was it built for?

Cheers
Richard

 

[Blagard]

From the sound of it the fireplace is currently unsuitable for an open fire.

First of all is the flue big enough? Extract from the BFCMA guide
"it is recommended to have a minimum internal flue size of 185mm square of 200mm round, as this size is suitable for most solid fuel burning appliances and also gas fires.
These are the minimum sizes for a flue above a fireplace recess or for an open fire with an opening up to 500mm wide by 550mm high. For large open fires, such as inglenooks. dog grate installations or special appliances I stoves designed to operate with a fire opening greater than 500mm x 550mm. the flue size should be between 14% and 16% of the free unobstructed area of the fire opening"

Next is the opening itself suitable? Again an extract from the BFCMA guide
"For open fires a suitable throated front lintel and gather must be provided above the fire opening, so that the front, back and sides slope up smoothly into the flue opening in the chimney at an angle no greater than 30 degrees from the vertical. Avoid flat surfaces or shelves which can cause turbulence"

Obviously the flue needs to be free of obstructions as well.

Finally check that there is an adequate supply of air
"As a guideline a permanent air vent with an opening or openings giving a total free area of at least 550mm2 per kW of rated output above 5 kW must be provided for open fires. Generally the same size of ventilation is used for room heaters or stoves, but always refer to the appliance manufacturers recommendations and Building Regulations.

This is important as air starvation will cause poor combustion and create problems similar to down draught and spillage of smoke and fumes back into the room, which can be unpleasant and dangerous. "

 

[stuart45]

You have a concrete raft lintel, which is not suitable for an open fire as it stands.
However you can adapt the opening with precast pieces.

 

[Architexeter]

Making an open fire draw is a fine art, I've just done mine (having removed a Parkray appliance) and there are so may variables specific to your chimney. Try and read as much as you can on the subject and then keep trying to vary things until you get improvements. I was in my chimney opening for days trying to get better angles, smoother edges, raising the hearth to reduce the aperture and ended up also constructing a throat. My chimney is short and there are trees nearby, I have now got it drawing but its still a bit smokey while the chimmo warms up - next job is to replace the pot with a taller one.

As everyone states, make sure the construction is suitable for an open fire.

 

[meanwhileinhell]

Hi, thanks to every one for the replies and lots of information! Very useful stuff. Remember, the current set up was in place before we bought the house, we have changed nothing except removing the stove.

@Blagard: Thanks for the link, some good information in there.

@Richard: The house was built in the 1890's, but with the current concrete raft lintel it has been altered for a stove. I have seen the original metal headers that the fire places originally had, as our dining room one is still present (since been blocked up, but we got it replastered so had it back to the brick).

@Stuart: Yeah I was worried that the current setup was unsuitable. I didn't realise that you could buy precast pieces. I always thought that there needed to be some sort of funneling type of adaptation to angle any smoke to the hole. Would you have any links to products, or names of parts that I could search for?

@Architexeter: The actual grate of the fireplace is quite small so the majority of the fireplace is decorative rather than functional, if you know what I mean. We have quite high chimneys with no trees nearby. I'll get researching ways to play with it.

 

[stuart45]

@Stuart: Yeah I was worried that the current setup was unsuitable. I didn't realise that you could buy precast pieces. I always thought that there needed to be some sort of funneling type of adaptation to angle any smoke to the hole. Would you have any links to products, or names of parts that I could search for?
t.

You need to buy a precast concrete throat unit with a removable front, and a fireback.
Build a couple of brick piers to hold the throat unit. Fill in behind the fireback with vermiculite/cement mix.