Explanation of basic physics and how does wood stove work?

[makaron16]

Hello everyone. Recently on Youtube I came across a couple of those "me living in log cabin" videos. And then I understood that I know nothing about how does a fireplace/wood stove work. I have countless questions which I tried googling and youtube-ing. But it seems that you either get "Bro just do this, that and that, ummm, because of I dont know, but trust me bro" answers, or no answers at all. So Im wondering if theres an in-depth resource that actually explains the physics behind wood stove or fireplace. Any help appreciated!

 

[Whitenuckler]

Hello everyone. Recently on Youtube I came across a couple of those "me living in log cabin" videos. And then I understood that I know nothing about how does a fireplace/wood stove work. I have countless questions which I tried googling and youtube-ing. But it seems that you either get "Bro just do this, that and that, ummm, because of I dont know, but trust me bro" answers, or no answers at all. So Im wondering if theres an in-depth resource that actually explains the physics behind wood stove or fireplace. Any help appreciated!

Are you talking about the chemical reaction formula's and such? It's been a long time since I've taken chemistry, but if I remember it's oxidation. Organic material, oxygen and heat. The stove provides the place to retain the heat and get air flow. More heat is released from the process once it's in combustion.

 

[EatenByLimestone]

Or maybe you’re looking at how the chimney draws air into the stove to support combustion?

 

[makaron16]

Thanks for the replies fellas. I didnt mean chemistry, realeasing energy, oxidation and all that jazz. I have a lot of questions about the basics. For example.
1. Why wood stoves have more than one door? Shouldnt one be enough? You open it, put the firewood, do some stuff, and later you clean the ashes/cold charcoal. Why have grid through which ashes fall into a container?
2. How and when does overdraft happen?
3. Why some wood stoves dont have regular shape exhaust pipes? Sometimes they are angled, or have even 90 degrees. Because the quicker you remove the combustion byproducts, the quicker you can do a new "cycle" of combustion. You know, just like in a car.

 

[Murray01]

Simplistically, hot air rises. Cool air is sucked in thru the bottom to feed the fire and the hot exhaust rises out the chimney. Different manufacturers have refined their wood stove design to extract the most heat and minimize emissions.

 

[makaron16]

Simplistically, hot air rises. Cool air is sucked in thru the bottom to feed the fire and the hot exhaust rises out the chimney. Different manufacturers have refined their wood stove design to extract the most heat and minimize emissions.

Thanks. But it doesnt quite make sense. If you have an internal combustion engine, the fresh air is forced into it because of atmosphere pressure (hence "naturally aspirated engine"). But when it comes to a fireplace or wood stove, then atmospheric pressure magically disappears? No, its still out there. So the fresh air isnt being pulled, its being pushed. Thats how I understand it

 

[begreen]

The driving force behind the fire is the draft which is suction on the flue. The vacuum created by the draft pulls air in through the primary and secondary air feeds.

Note that in a naturally aspirated ICE the air is also pulled in, not by atmospheric pressure, but by the vacuum (suction) created by the downward movement of the piston(s).

 

[stoveliker]

Pulled or pushed doesn't matter.
Air flow is ignorant of what we consider "normal", what we define as the zero.
Air flows from high pressure to low pressure. Whether due to being compressed and flowing to atmosphere, or from atmosphere to a (partial) vacuum.

In a stove a low pressure is created by the rising warm air in the chimney. As a result, air flows into the stove because the air pressure in the room is higher than in the stove.

(And this can lead to issues in a basement where,.due to warm air rising in a home, the pressure can also be lower. It then depends on where the pressure is lower, stove or basement - that determines whether smoke goes up the flue or rolls out of the stove.)

 

[EatenByLimestone]

Thanks for the replies fellas. I didnt mean chemistry, realeasing energy, oxidation and all that jazz. I have a lot of questions about the basics. For example.
1. Why wood stoves have more than one door? Shouldnt one be enough? You open it, put the firewood, do some stuff, and later you clean the ashes/cold charcoal. Why have grid through which ashes fall into a container?

Sometimes it’s just for style. Think 4 door car vs 2 door car.

Other times there is an ash door as a second door. This can be put there for convenience. Wood stoves don’t need them. A coal stove needs to have the ash fall away and needs air fed below the coal, so they need the grate and lower door.

2. How and when does overdraft happen?

Overdraft is the condition when a stove gets too hot. This can happen from user error operating the stove, too much draft, or wood that is too dry. Sometimes all 3 contribute at once.

3. Why some wood stoves dont have regular shape exhaust pipes? Sometimes they are angled, or have even 90 degrees. Because the quicker you remove the combustion byproducts, the quicker you can do a new "cycle" of combustion. You know, just like in a car.

Wood stoves have a larger exhaust pipe than a car does. Sometimes the exhaust needs to be routed around parts of the house framing, or out the side for aesthetic reasons. The simpler the path the better, but you can work around this.

 

[Rearscreen]

Wood stoves have a larger exhaust pipe than a car does.

I dunno, I've seen some big pipes coming off of pick'em up trucks that compensated for the drivers anatomical deficiencies.