The word "draft" refers to the hot air movement that circulates in your stove's exhaust system, going from the stove to the outside of the house, and carrying with it the combustion residues. The draft is a natural phenomenon. Hot air weights less than cold air, causing it to rise. This is why the higher the temperature in the exhaust system, the stronger the draft. It is also important to say that the "tunnel effect" created by the exhaust system contributes to increasing the draft effect. This is why chimneys that are excessively long often create excessive draft, while chimneys that are abnormally short will have an excessively low draft.

"Negative pressure" can be seen as a "reverse draft". That is, air will circulate from the chimney toward the interior of the house. Negative pressure is often what causes smoking problems. In general, negative pressure is the result of either one or a combination of the three factors explained below:

A cold chimney. Cold air, which is heavier that hot air, has a tendency to go down the chimney and create the effect of a "clog". This explains why a stove that has not worked for a long time and which chimney is very cold will sometimes be hard light.

Negative pressure can also occur as a result of a "vacuum effect" in the room or the house. The air in a house is constantly moving. Hot air rises, cold air moves down. Air can also be expulsed outside of the house with the use of air-moving equipment, such as a range hood, a air exchanger, a bathroom fan, a dryer, etc. Furthermore, air goes in and out of the house through cracks, doors, windows, etc. If air leaves a room without being replaced, a "vacuum effect" is created. Therefore, if a house is well insulated and all windows are closed, the room will source its air through the easiest alternative route, which is often your stove's exhaust system. This creates a negative pressure in your exhaust system. You now understand why it is often suggested that a window be slightly open in the room where the stove is located. This enables the room to easily source its air outside the house without searching for an alternative route. The vacuum effect can be amplified when your stove is located in the basement. This is due to the fact that your house itself acts like a chimney. Since hot air will rise to upper floors in the house, it will "draw" air from the basement of the house. This is called the "chimney stack effect".

Wind can also be a third cause of negative pressure. When your house is located near a structure which height is superior to your chimney's, wind currents can create an interference with your chimney, leading to negative pressure problems.



DRAWING #1B

DRAWING #1B shows a stove functioning under normal and adequate conditions. Heat rises to the upper floors and the room where the stove is located has an adequate supply of oxygen. The chimney draft is sufficient and the combustion gases are evacuated normally through the exhaust system.

DRAWING #2B

DRAWING #2B shows the effect of a cold chimney. Cold air creates a reverse draft (negative pressure), which causes smoking problems. This phenomenon is amplified by the fact that heat rises, which creates a draft from the basement of the house to the upper floors ("chimney stack effect").

DRAWING #3B

DRAWING #3B shows the effect of negative pressure caused by an air-moving device inside the house. In the example above, the range hood draws air from inside the house, which is replaced by air coming from the chimney. The result is a smoking problem.

DRAWING #4B

DRAWING #4B shows the negative pressure effect caused by wind, influenced by nearby structures such as a building.

DRAWING #5B

DRAWING #5B shows the negative pressure effect that can be caused by wind, influenced by nearby structures such as a tree.

DRAWING #6B

DRAWING #6B shows the minimum height that the chimney should have, considering adjacent structures located within a horizontal distance of 10 feet.