The top-down method of building a fire in an open fireplace simply reverses the way traditional fires can be built. Where the logs can traditionally be laid at the top of the fire, when using the top-down fire method the logs are placed in the fireplace first. Kindling and the fire starter are then added on top the logs respectively. In the case of trying to improve the draw on a fireplace, the main benefit of building a fire using the top-down method is that the fire is started at the top.
By being able to light it at the top of the fire, the flames are concentrated further towards the top of the fireplace. This allows all of the initial heat generated by the fire to be used to warm up the air within the chimney, and help start the draft. In a traditionally built fire, the fire is started at the bottom of the fireplace.
The fire starter will have kindling and logs laid on top of it, meaning that the heat needed to start the draft may not be produced until later into the fire. Wet wood is harder to burn because the excess moisture content needs to be burnt off before the wood can be properly combusted.
As a result, it can be harder to start the draft on a fireplace when burning wet wood because less heat is initially being produced. You can measure the moisture content of your wood accurately by using a moisture meter. A moisture meter is an essential tool for any fireplace. While it may seem that larger sized fires can produce more heat to start the draft on a fireplace, well-burning smaller sized fires can be more beneficial than larger sized fires that struggle during the early stages of a fire.
A smaller fire can get going much more quickly than a larger sized one. We can always add more wood once the fire has got going and there is sufficient draw on the fireplace from the chimney to sustain a long and successful fire. Another common way a chimney passageway can get blocked or partially closed off is by the accumulation of excessive creosote, the soot build-up that can cause chimney fires or blockage. Creosote is dangerous in itself, but it can also cause the combustion gases to back up and add to the existing problems.
Creosote buildup on the spark arrester is also another way for the chimney to become blocked. This soot build up on the metal screen can accumulate enough so that it will close off the small openings entirely. A chimney with a clogged passageway or a plugged up chimney cap works like hose with a closed nozzle on it — the harmful gases are not allowed to escape and have no choice but to back up into the home.
These cute little critters can create havoc with nesting blockages. Another potential reason for a chimney draft to not work effectively could be from the firebox size or location. The firebox must be the correct size to correspond with the chimney flue the passageway within the chimney walls that the smoke travels through in order to most effectively pull all of the unwanted gases and smoke into the outside atmosphere.
There is a rule that the flue should have at least a ration with the firebox so that the system works correctly. Therefore, for every 10 square inches of the firebox there should be at least one square inch opening in the flue.
The firebox must also be kept in the correct location for the smoke to exit in the intended manner. The fire should be kept no more than one inch away from the back of the firebox wall.
Simply starting the fire more towards the back wall in the fire grate may correct this problem instantly. The fire must also always be made in a grate to provide it enough oxygen, without a fire grate it will smoke and not get hot enough to ventilate properly.
A fireplace with an incorrect design can also affect the draft of your chimney. Fireplace codes are in place to ensure every part of your home is installed correctly.
If these codes are not followed correctly, problems may occur. Some of these issues may include, as previously discussed, improper firebox to flue ratio. Along these same lines, the firebox could also be manufactured incorrectly itself.
If the firebox is too shallow, typically less than 20 inches, then smoke and combustion gases may enter the room without a chance to leave through the appropriate flue. Getting the constriction just right used to be a real artform. These days it is a science and we see the venturi principle used in many ways such as pulling petrol into your car engine using a venturi in the design of a carburretor and drawing air in to mix with the gas in the burners of your gas stove.
Now I am sure you are reading this and thinking what on earth is the relevance of all this. Well I have come across people that want a fire place however they find it almost impossible to find a person with the knowledge to build a flue that works correctly.
People don't understand and hence the builder who thought that you need to install a fan. If you have a chimney that doesn't draw properly or you wish to build one you need to build the flue with a narrow part above the fireplace at the bottom of the chimney.
It is a good idea to make it in such a way that you can easily modify it later if you need to just in case you have not got the correct amount of constriction.
Start off with a constriction that is half or two thirds the size of the rest of the chimney. Light the fire and try it and adjust it as necessary. You need to find the sweet spot with a good compromise or you could install a "Damper.
In the days when most houses had fireplaces and chimneys the chimney would usually have a "damper" installed to change the size of the constriction in the flue and in this way control the fire.
A damper was either a piece of cast iron cast iron withstands the heat better than steel that slid across the flue or turned like a butterfly valve in the flue to restrict the flow. As you increased the constriction you could increase the amount of draw and get the fire roaring - very useful when first lighting the fire or quickly heating the room up. But as you increase the constriction further you would reach a point where further constriction would "dampen" the fire slowing down the rate of flow up the flue and this would save fuel, it would make the fire burn slower and use less coal or wood.
A good rule of thumb is to think about reducing the air escaping high in the house and increasing the air coming into the house on the lower floors. Note, it may make a difference which window you open or close, especially in a breeze — when you open a window, check to ensure the outside air is actually flowing in.
Modern houses tend to be very tight think spray foam insulation, house wrap, weather-sealed windows, etc. Because these homes are so tight, it is difficult for ventilation and combustion air to easily enter the home, meaning that there is not enough makeup air in the house for the fireplace to draw properly. Then add ventilation air opening a downstairs window that is blowing air into house, etc. Going through this process will help you determine how much air is needed for the fireplace.
While the quantity of combustion air required varies based on the type of fireplace, type of chimney and size of the fire that is burning, a general rule of thumb is 1 cubic foot per minute of make-up air per 1 square inch of flue area. For a permanent fix, you can install one of the following:. Two of the most common weather culprits are extreme cold and cross drafting.
In very cold temperatures, an unused flue can fill up with high-density cold air that itself blocks the flow of smoke up the chimney. This is especially true if your chimney is located on the outside of the house. In these cases, take steps to "warm" your flue by building a small fire of newspaper at the back of the firebox. Continue to feed more newspaper until the smoke from the fire disappears up the flue.
Wind can cause smoke issues a couple of different ways. The first way is known as Dynamic Wind Loading. This is caused when wind blows on one side of the house, causing a high-pressure zone on that side of the house and creating a corresponding low-pressure zone on the other side of the house. This causes a pressure differential, which can be solved by opening a window on the windward side of the house.
Wind can also cause turbulence at the top of a chimney, not allowing the smoke to escape, or can even blow the smoke back down the chimney into the fireplace. This is especially common if there are tall roofs or trees nearby. You can fix this by replacing your rain cap with a draft inducing cap. The stack effect describes the movement of air into and out of the building, chimneys, stack, etc. In most homes, there is typically a neutral pressure level about halfway between the ground floor and the roof, meaning everything above that level is positively pressurized air will leak out and everything below is negatively pressurized air will leak in.
In older houses and oftentimes tall houses, the negative pressure rarely exceeds 8 Pascals, which is about the difference in pressure in 10ft. Furnaces and fireplaces usually perform well pulling against a negative pressure of up to 8 Pascals. Modern houses, however, tend to be more tightly built using spray foam insulation, caulked windows and sealed doorways.
They also tend to be full of powerful kitchen and bathroom exhaust fans, so the neutral pressure level may be higher in the house if it exists at all. This means the negative pressure in the lower areas of the house can far exceed 8 Pascals, causing a downdraft in a chimney. You can help reduce stack effect in your home by stopping air leaks in the uppermost parts of your house, including attic access hatches, ceiling light fixtures, and poorly fitting windows. In this case, the stack effect can only be corrected by adding as much air to the house as is being blown out of it, i.
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