Condensation or damp

[IWalkLikeHimaMartian]

The air entering the disused chimney at the bottom is warmer than the air within the chimney, therefore the RH of the air changes in the process.
Again from my paper, (with appropriate references as included in my original paper, woody!)
View attachment 142398
: http://ocw.usu.edu
A change of about 10°C doubles or halves the RH.
The warm entering at the bottom may be at about 20 - 25°C at about 45 -75% RH. It has the ability to absorb more moisture, especially from the fabric of the building ( the chimney) which may have a high moisture content.
The warm'ish air with a high RH is then ventilated out the top of the chimney, carrying with it any excess moisture that it has accumulated.
Warm air naturally rises.

BTW, in an unoccupied property the air at the bottom of the chimney will be no warmer than the air at the top or within the chimney. Therefore there will be no natural draught, or even a downward draught.

 

[blup]

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[IWalkLikeHimaMartian]

.fancy using a user name like that !!!!! Walks with turkeys, Imamartion, himmagin and wannabe will be very very cross with you

Terribly sorry, old fruit. But I cannot change it again now for about another 175 days.

 

[motorbiking]

BTW, in an unoccupied property the air at the bottom of the chimney will be no warmer than the air at the top or within the chimney. Therefore there will be no natural draught, or even a downward draught.

There could easily be draft caused by the prevailing wind overcoming a pitched roof, creating a pressure difference.

 

[IWalkLikeHimaMartian]

There could easily be draft caused by the prevailing wind overcoming a pitched roof, creating a pressure difference.

You are just trying to make it to the pedants' corner.
If the temperature of the air travelling up the chimney is at, or about the same temperature (therefore we can assume similar RH), that draught (caused by the prevailing wind overcoming the pitched roof....etc, there will be negligible affect on the reduction of humidity in the chimney.

But we could both try to make it to the pedants' corner by discussing draft and draught.

 

[EFLImpudence]

There could easily be draft caused by the prevailing wind overcoming a pitched roof, creating a pressure difference.

Not only the roof.

The wind around and over chimney pots causes low pressure which creates upward flow. That's why they are there.

 

[IWalkLikeHimaMartian]

Not only the roof.

The wind around and over chimney pots causes low pressure which creates upward flow. That's why they are there.

That is why you sometimes get a down draught?

 

[transam]

That is why you sometimes get a down draught?

and cause intermittent flue spillage