Why do smoke and hot air go up a chimney?

Why do smoke and hot air go up a chimney?

You probably are wondering if there is any science behind a good chimney draft. Why is the smoke going up the chimney instead of going all over the place in your room? Anyone who has ever lit a fire knows that while most of the smoke goes up, some of it still travels to other areas of the room. So why, with chimneys, most of the air goes outside?

If you’ve studied physics and convection before, you know that warm air will expand and then begin to rise because of buoyancy. This is why the ceilings of the room tend to have warmer temperatures as compared to the floor. Warm air goes up, cold air goes down. This is often referred to as the stack effect, and the rest is up to wind and traveling air.

If the home is insulated properly, with no way for the smoke or air to escape, then it would probably travel through the whole room. However, one more law of physics says that it’s not the cold air that comes in; it’s just the cold air that goes out. Therefore, when you crack open a window, all that will happen is that the warm air will get out.

The same thing happens with chimneys. When you are burning a fire, there is a lot more smoke and hot air as compared to your traditional radiator – so, while some of that air will efficiently warm up your house, the rest will have to find a way to be released. Chimneys offer that “escape route,” and when the hot air finds that flow, it will automatically go up. It is simply a result of that stack effect we are talking about.

If a chimney is constructed properly and allows for airflow, then the smoke and hot air will go up. If it’s constructed poorly or has a blockage, then you may need to bring a chimney pro to take a good look at it. 

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