Smoky fire question.

[Manks]

Hi All

We have a new fireplace in our new sitting room. We have tried to be fairly neutral, with a brick-lined big hole and a local stone surrounfd made by our local stonemason. A swan's nest and dogs completes the setup.

I anticipated that the fire would not be as efficient as our old Victorian combination, which draws like Tony Hart on speed, and I was right, it is somewhat fickle.

If I warm it up slowly, it is not too bad. But we do get the occasional puff of smoke into the room until the fire is hot.

Even when the fire is hot, however, the smell of the fuel is quite strong. So, the smell of logs or coal fills the room. This is not as delightfully rustic as it sounds.

If I understand fireplace technology correctly, the problem we have is because of the large distance between grate and flue. I'd guess it's 40".

So, what to do? Raise the basket on a platform? Have a metal insert made? I don't know. What I do know, however, is that we cannot continue with it as it is.

Does anyone have any practical advise here please?

Manks


PS, the flue is a pre-cast unit, the chimney is sectional concrete and we have a crown pot. Also, the initial smoking seems to be helped by opening a window.

 

[MdB]

... Also, the initial smoking seems to be helped by opening a window.

This statement strongly suggests that you don't have enough ventilation in the room. To get the smoke to go up the chimney, requires that there is a strong air flow up the chimney. This can only occur if the air can get into the room from somewhere which leads to the outside.

Lack of oxygen in the room (caused by the fire burning up all that is available due to lack of ventilation) will cause the fire to produce carbon monoxide. It is therefore very important that you get the ventilation issue sorted.

Its a boring document but I suggest you read the following:
http://www.planningportal.gov.uk/england/professionals/en/4000000000503.html

It may help you with your other issues too.

 

[Manks]

MdB

You may be right. The windows have a "trickle vent" position, which is required by building regs. But maybe I need to introduce a meatier vent somewhere near the fire?

Manks

 

[ian]

If I understand fireplace technology correctly, the problem we have is because of the large distance between grate and flue. I'd guess it's 40".

That is quite a distance. It sounds like a large hole if you can fit a swans nest in. Do you have a hood/collector channeling into the flue? You say that it does not draw when you first light it but if you warm it slowly it comes good is probably because the liner is cold and the natural tendency of hot air to rise is opposed by the down draft. Once the liner warms a convection cycle gets going. I think distances from fire base to lowest aperture, i.e. hood base etc are recommended in the 24 to 30 inch range. If a canopy is not asthetically desirable, I seem to remember a neighbour who had a fit for purpose electric fan somewhere in the flue to help the draw.

 

[Manks]

Ian

I have wondered about a fan, but a "mechanical" solution is preferred, so I might mess around with basket height or (and this would have to be done well) have a planished "semi-hood" made. It would ideally be silver coloured, so I am not sure what could be used. I think it could look very nice, and in keeping, if done well.

Manks

 

[Nemesis]

Fans can be noisy.

If you have a suspended floor, it may be possible to bring in air via an air brick under floor to a grille near the fire to provide some draught, although chimneys can be a bit of a black art really, especially large holes which need some sort of 'gather' to get smoke going up the chimney. Such things as height of pot and even overhanging trees can all make chimneys not draw.

 

[Mark]

... Also, the initial smoking seems to be helped by opening a window.

This statement strongly suggests that you don't have enough ventilation in the room. To get the smoke to go up the chimney, requires that there is a strong air flow up the chimney. This can only occur if the air can get into the room from somewhere which leads to the outside.

Lack of oxygen in the room (caused by the fire burning up all that is available due to lack of ventilation) will cause the fire to produce carbon monoxide. It is therefore very important that you get the ventilation issue sorted.

Its a boring document but I suggest you read the following:
http://www.planningportal.gov.uk/england/professionals/en/4000000000503.html

It may help you with your other issues too.

Im not sure I agree with all of that. It is likely that before the fire is started you already have airflow ventilating the room down the chimney and then out (Its easy to check this).

When you light the fire you need to reverse this flow, and until the flow is reversed then the smoke will come into the room. That isnt going to happen until you get the chimney full of hot air. In the meantime opening a window gives a bigger airflow into the room so will help the airflow reversal in the chimney.

How big is the flue? The fact that you have an ongoing smell even when the fire is going suggests that it might not be big enough although I also think that 40" is too big a gap.

when you say you replaced a combination - whats a combination? A stove?

 

[ian]

I have made a couple of canopies / hood from 4mm sheet aluminium, (check the Yellow pages) though in my case they were finished with aerosol matt stove paint. They were fairly easy to cut and form, but with enough rigid strength to work without folding up and creasing. Someone else here may be able to help with the technique for finishing the surface "au natural"

 

[Nemesis]

When you light the fire you need to reverse this flow, and until the flow is reversed then the smoke will come into the room.

There still needs to be an adequate source of air coming into the room. Many rooms are now so draughtproof that it can cause problems with air flow to chimneys.

It's probably worth mocking up any canopy/hood design in card before committing to the metal. too.

 

[Manks]

I have wondered whether the stone surround is sufficiently low where it cloaks the lintel. It appears that the smoke entering the room is hitting the lintel and "bouncing" into the room. If the surround had been made six inches deeper at the front, it is possible that the surround would act as a hood.

But given that the flue and surround are now installed, I think it's a case of making it work somehow.

I have raised the dogs up on bricks (on edge) and will see if it helps.

Manks

 

[MdB]

MdB

You may be right. The windows have a "trickle vent" position, which is required by building regs. But maybe I need to introduce a meatier vent somewhere near the fire?

Manks

The trickle vent in the windows is required to supply you with oxygen. A fire will need much more than this.

As Nemesis says, old properties used to have so many drafts that ventilation for fires wasn't a problem (nor was condensation for the same reason). Now that people like a lot warmer homes, all the drafts are blocked up and ventilation becomes an issue (as does condensation).

A vent doesn't have to go directly to the outside but there does have to be a clear route for the air. A vent into the garage and then to the outside will help reduce drafts and will warm up the air a bit before it comes into your room.

 

[Manks]

With the dogs on bricks and the window open when I lit the fire, I have not had any problems today. But one swallow does not a summer make and I want to see how things go over a week or two.

Manks

 

[Nemesis]

I'd get a carbon monoxide alarm - shouldn't cost much, but worth it. Silent but very very nasty stuff is carbon monoxide. See what is happening to the air when the fire is lit.

Try also taping some card along the lintel, to artificially lower it. You frequently see a piece of toughened glass installed in 'stately home' open fires to reduce the height. Worth experimenting.

How is the smoke being introduced into the flue? Is there any 'gather'?

 

[bower1]

A vent into the garage and then to the outside will help reduce drafts and will warm up the air a bit before it comes into your room.

Surely this will draw fumes from the recently parked car into the house. Thats assuming anyone parks cars in their garage.

 

[MdB]

A vent into the garage and then to the outside will help reduce drafts and will warm up the air a bit before it comes into your room.

Surely this will draw fumes from the recently parked car into the house. Thats assuming anyone parks cars in their garage.

Good point. Our vent goes through the garage which is why I mentioned it. The garage has a dirt floor though and is only long enough to fit a mini (which I don't own) so exhaust fumes are never anything to worry about.

 

[MdB]

With the dogs on bricks and the window open when I lit the fire, I have not had any problems today. But one swallow does not a summer make and I want to see how things go over a week or two.

Manks

Others have mentioned in the past that having a warm chimney helps. i.e. day 1 / day 2 the performance isn't great as the chimney is cold. Day 3 / day 4 performance improves as the chimney is still warm from the previous days.

 

[bower1]

But you are right about drawing from another room, maybe a utility room. Best if its not a toilet/bathroom due to odours.

 

[Manks]

<i>Try also taping some card along the lintel, to artificially lower it. You frequently see a piece of toughened glass installed in 'stately home' open fires to reduce the height. Worth experimenting. </i>

I didn't know this. So our forefathers also weren't too clever at getting lintel height right?

<i>How is the smoke being introduced into the flue? Is there any 'gather'?</i>

Yes and no. Sitting between two lintels is a pre-cast "throat" which leads into the chimney. But the lintels themselves are just concrete and sharp-edged.

I have just had our builder round, and he is fitting two air bricks for me on Thursday.

Manks

 

[Nemesis]

Air bricks leading where?

They need really to be under the floor with a grille near the fire if a draught isn't to howl across the room.

No our forebears weren't great really at fire design, it took Count Rumford and Ben Franklin to do some work on the science before fires became efficient. Long history from a central fire with a hole in the roof to where we are now.

Still not as efficient as a firebox or stove though.

However, in the past flues probably didn't get cold, which was a help.

http://www.soliftec.com/heroes.htm

 

[Manks]

Air bricks opposite one another in the wall. Yes, there will be a draft, but better that than losing the family to carbon monoxide.

There are cupboards either side of the breast, so we COULD put them in there with another vent in the cupbaord doors, but it would not be elegant.

Manks