# A question about temperature and wind motion, and hello!

RyanJH
First of all, just registered, first post. So hi all, just started undergrad course in physics at kent so may pop up here quite a bit :)

So, I was just outside, having a smoke, standing in the doorway of the house. Now I've noticed this before and not thought it about as much but the smoke from my roll-up always flows back in to the much warmer house. From my understanding of thermodynamics heat always flows from hot to cold. So I would expect the smoke to all go away from the house as outside is considerably colder.

I had some thoughts trying to explain it but won't chance my arm hehe. So, anyone know or have an idea as to why this is?

Staff Emeritus
I'm not certain, but this is my best guess.

What you are witnessing is not heat transfer, but air movement. Hot air is less dense than cold air, and it rises and leaves the house near the top, while cold air enters from the bottom. (Your house is not air tight)

I could be incorrect, so hopefully someone else can clarify.

Mentor
heat always flows from hot to cold.
This does not mean "hot things flow from hot to cold" - it means that hot things in contact with cold things will cool down, and transfer energy to the cold things.

Your smoke just follows the air flow. Two possible reasons why it enters the house there:
- you have another open door/window somewhere else, and wind flows through your house
- you have another open door/window above that door, and hot air flows upwards (similar to a chimney)

SW VandeCarr
First of all, just registered, first post. So hi all, just started undergrad course in physics at kent so may pop up here quite a bit :)

So, I was just outside, having a smoke, standing in the doorway of the house. Now I've noticed this before and not thought it about as much but the smoke from my roll-up always flows back in to the much warmer house. From my understanding of thermodynamics heat always flows from hot to cold. So I would expect the smoke to all go away from the house as outside is considerably colder.

I had some thoughts trying to explain it but won't chance my arm hehe. So, anyone know or have an idea as to why this is?

If you had fire going in your fireplace and opened a window on a cold winter day, which way you would expect the air to flow through the window?

Mentor
I think a more likely effect is that hot air is flowing up and out through the top portion of the door opening, and cold air is flowing in through the bottom portion of the door opening.