General Draft Question
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I bet it is because the colder the outside air gets, the heavier it becomes. The hot flue gases become relativly lighter in this case and rise up the stack faster.
Just a bet.
Just a bet.
That would about sum it up. Humid air is also less dense than dry air, so you may notice a similar effect if you have a humid/rainy day. I only have ~13' of flue so those rainy spring days when the outside temp is ~50F and I just need to take the chill off are the worst for good drafting.
BJ64 said:
Okay - I can deal with cold air being heavier...even though I don't understand exactly how they weigh it....My mind just can't grasp why hot air would be able to displace it faster when it is colder out. Wouldn't the heavy colder air press down on the lighter air and make it harder for the hot air to rise???
In order to try to comprehend this, science was not my forte, I have to imagine an object that I can actually see...a big rock for instance sitting on a light feather. That feather isn't going anywhere fast.
Why is it air acts differently?
cozy heat said:
Humid air affecting draft is easier for me to comprehend as I imagine it 'pressing' down on things due to the water in it. Makes sense that heat from the fire would have a harder time 'pushing' it up out of the chimney. A battle between the two opposing forces.
perplexed said:
Air is weighed with barometric pressure. The lighter (heated exhaust) is so much lighter than the heavy cold air, it causes it to draft or rise even faster. If you try to run your stove on a 100* day, the difference in pressure is so little, that the air from your stove will not rise fast enough to vent the gases and most likely will have a hard time drafting. Is this making sense? Airplanes and wood stoves perform at their peak in cold weather. Airplanes achieve greater lift and stoves achieve greater draft.
Since cold air surrounds the hot air there is no real 'pressing down' or 'pushing up'. The smoke rises for the same reason a cork bobs to the surface of water...the cork is lighter than the volume of water it displaces. Likewise, the hot air in the flue is lighter than the cold air it displaces. The greater this difference in density, the greater the buoyancy.
Entire books have been written on this single subject. You may try and google 'buoyancy' for general descriptions or 'lapse rate' if you really want to dive into some specifics.
Entire books have been written on this single subject. You may try and google 'buoyancy' for general descriptions or 'lapse rate' if you really want to dive into some specifics.
Warmer air is more "boyant". The heavier the outside air is, the more boyant the lighter air is.
Think about a toy ballon filled with a little helium and some air- it will rise in air slowly. Put it underwater and it rockets out, even though the water is so dense.
Think about a toy ballon filled with a little helium and some air- it will rise in air slowly. Put it underwater and it rockets out, even though the water is so dense.
perplexed said:
I know how to explain it.
See how skinny AP is in his avatar just above this post. Think of him as hot air and he is standing on one of a teeter-totter. Now then, think of some big boys like Rick and I as being cold air. We are a little heavier than AP. We decide to leap out of a barn loft onto the opposite end of the teeter-totter to send the unsuspecting AP to the moon.
That should also explain the name Adios Pantalones.
Barometric pressure weighs the air by comparing it with a vacuum. A column of mercury creating a vacuum at the top falls only so far because the weight of the atmosphere pushes against it. Replacing air with water helps to understand the concept. Think deep sea diving...perplexed said:
In the open space that is the sky, no... the air is too slippery to contain. In the confines of your chimney however, the rising hot air can cool along its journey, becoming heavier and losing buoyancy. In such a confined space, you can have stratification of thermal inversion where the cold air on top weighs down on the warmer air trying to rise.perplexed said:
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