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The Smoking Fireplace


In these pages we will look at the causes and possible remedies for the discharge of smoke and fumes into the room from solid fuel open fires and appliances only. They do not refer or apply to gas fires or appliances. So lets first look at the Main causes for a fireplace smoking into your room and later we will consider a number of other reasons.


The Main causes of the Smoking Fireplace.

 1. Fireplace is too big




If the fireplace is too big for the size of the flue, then the large quantity of fumes building up in the oversize fireplace can be too much for the flue to carry. Flues more than 6m tall should normally be not less than 1/7th to 1/8th of the area of the fireplace opening; to illustrate a flue of 9 inch diameter can serve a fireplace opening up to about 22 x 22 inch. For bungalows with shorter flues this ratio ought to be reduced to 1/6th As it is normally unrealistic to increase the flue size, the fireplace size must be reduced. There are several ways this can be done, subject to the size of the original opening and the purpose for which the fire is intended. For very large fireplaces like inglenooks, the whole flue might be closed off with a horizontal register plate just above lintel height. An insulating liner installed above it and a freestanding fire Such as a Rayburn Rembrandt, (See Figure1.) Or a built-in convector open fire, such as a Jet Master or Turtuise, or even a closed Multi Fuel stove, can then be fitted with a flue pipe projecting through the register plate, and connecting to the insulated liner.

 For smaller fireplace openings say up to maximum 3ft square, a smoke hood, canopy or tempered plate glass strip, can be fitted across the full width of the fire opening, thereby reducing the height of the lintel. You might try experimenting first, by using a strip of sheet metal, or fireproof board pinned or wedged into position. (Combustible material should not be used even temporarily.) This can be lowered until the fire no longer smokes back. Once this has been achieved you can make a permanent job of it. Try the experiment for a few weeks before considering it a success. An alterative would be to raise the fire bed to reduce the opening size. This can be temporarily built using old bricks filling the gaps with sand. Or you might try both in this situation.


2. Air starvation and room ventilation


The problem of air starvation or the lack of room ventilation is often over looked.

 All fires must have oxygen to burn. Since air contains about 20% oxygen. Five times as much air is needed to give the needed quantity of oxygen for proper combustion. Also, open fires require substantial quantities of air to clear the smoke up the chimney.

 In modern homes solid floors are the norm, as are draught free doors and windows. It follows then that the lack of ventilation into the room is consequently a very common cause of the smoking fireplace, in both the modern house, and those that have been modernized.

 Attempting to burn solid fuel with inadequate ventilation will have two results:

 1st. If there is inadequate oxygen available for the fire, it will result in incomplete combustion. When complete combustion occurs, the products produced are Carbon Dioxide and water vapour. However a lack of oxygen will produce Carbon Monoxide, which is an odourless and highly poisonous gas.  

2nd. A lack of ventilation will mean there is not enough air available to replace that trying to be drawn up the flue in order to clear the smoke and fumes from the fire. Resulting in smoke and fumes spilling into the room, including the highly poisonous Carbon Monoxide.


How to increase ventilation to the room: 

If the fire works properly when the door to the room is open, but it smokes when the door is closed, then the problem is air starvation. This is not a defect in the construction of the fireplace or flue, but a lack of ventilation to the room. To cure this problem, additional air must be allowed into the room, you might vent directly through an outside wall, but this can introduce cold draughts. Better, is to vent into the hall using a “Draught Master” above the door, and then to outside. If the fire works well with the door to the hall open, then there is sufficient ventilation from the main house. A vent from the hall to outside is usually more acceptable than a vent from the living room direct to outside. If the room has a suspended wood floor with air bricks below to the outside of the house, then one or more grilles cut into the floorboards to one or both side’s of the hearth can be a good solution. The grilles must have enough free open area. Try to get half the cross section of the flue as a minimum.


3. Badly positioned chimey terminals  

The best place for a chimney to terminate is well above the ridge of the roof. Even so tall objects nearby can still affect it.

 Two different problems can occur with a badly placed chimney terminal, although the symptoms can be alike.


a. Down draught


In this position, the wind is blowing over a tall tree, or it could be a hill, or say, a block of flats, it descends onto the chimney top, causing smoke or fumes to puff into the room from time to time. For downdraught problems, certain types of pot can help reduce the problem or the construction of a slab top or dovecote top can help


b. Pressure Area 


In this situation the chimney is sited in the line of the prevailing wind, with the house roof, or it could be a tall building, behind the chimney terminal. This can cause puffing or even a continuous smoke spillage when the wind is blowing.


Pressure area problems can be more difficult to solve. The simplest way would be to raise the chimney until it is above the pressure zone. This can be done with a tall chimney pot. (Chimney pots are made up to (5') tall). On the other hand, if the chimney is much too low, you could raise the stack by 2 to 3 Feet and add a tall pot.


You should note that Building Regulations Govern the maximum height for a chimneystack, including pot, the narrowest width, measured from the highest point where it leaves the roof, would limit the maximum height of the stack.


You could try opening a small window on the windward side of the house, if this helps then fit a permanent air vent. Doing this helps to equalize the pressure at the top and bottom of the chimney.


If all else fails, then an electric chimney fan may be the only solution, however even this solution is limited. However one must remember that during an electrical power failure the fan will not work, and it is then that you might well need your fire must. This Pot is 5 foot tall. However it does put a lot of strain on the chimney stack, so care needs to be taken when considering this arrangement to lift the top of the flue out of a pressure area.


For more information, or advice, contact ADVANCED CHIMNEY SWEEPING Service's on 01482653418 

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