Chimney pot cowl on unused chimney: is it usually needed?

[Matt723]

Hi All

What's your take regarding installing cowl on chimney pots which are unused? I can't help thinking that when it rains heavily some water must go in the chimney and pool somewhere?

At the same time I see a lot of pots which don't and there are no damp issue.

In your experience what are the pros and cons of installing cowls on unused chimney pots?

 

[ree]

OP,
Yes, use vent cowls inserted into the chimney stack pots. Such as long lasting Redbank flue ventilator clay cowls - or a cheaper metal cowl from Colt say.
Cowls keep birds out, & ventilate the flue.
If the fireplace(s) below is blocked off then insert a Hit-&-Miss vent into the blocking - this will allow a through flow of air.

 

[Harry Bloomfield]

In your experience what are the pros and cons of installing cowls on unused chimney pots?

Disused chimneys need a rising flow of air, to allow them to remain dry. The top needs a pot, which keeps the rain out, but still allows that essential flow of air.

 

[Matt723]

Thank you both

I guess the part that puzzle me is how the pot itself, without some sort of "hat" (the cowl) keeps the water out?

Would rain drops not fall into the terracotta pot and the water would pool somewhere in the chimney?

 

[Harry Bloomfield]

I guess the part that puzzle me is how the pot itself, without some sort of "hat" (the cowl) keeps the water out?

Would rain drops not fall into the terracotta pot and the water would pool somewhere in the chimney?

Of course. Not a problem if the chimney has a fire lit frequently in it, but without the fire - it needs a cowl to keep the rain out..

 

[Matt723]

Thanks @Harry Bloomfield , that is what I thought.

That being said I'm looking around from the top roof window and see the vast majority of pots (I can probably see 200 pots all around the house on neighbouring properties) do not have cowls. I would bet none of those chimney is used anymore and am really wondering where does the water go and sit ..

Our chimney is not used and they are plastered on the inside (no clue how it is sealed inside, maybe with bricks and mortar) and we have no damp issue, although I am sure the water is in there somewhere until it dries out.

How is it possible that those houses have no damp issues whilst they don't have cowl?

 

[stuart45]

The amount of water that actually enters the pot is not that much. Older flues were parged up with mortar, so this soaked it up as it ran down. When flues have an S/S liner and woodburner it can run down into the stove though.

 

[Harry Bloomfield]

Our chimney is not used and they are plastered on the inside (no clue how it is sealed inside, maybe with bricks and mortar) and we have no damp issue, although I am sure the water is in there somewhere until it dries out.

How is it possible that those houses have no damp issues whilst they don't have cowl?

On Sunday we had 6mm of rain, this morning we had 2.9mm. A chimney pot might collect rain from an area of maybe 100 square mm, at a guess - maybe 1/2 a pint of water being unnecessarily poured down your chimney, and going into your home. Entirely your choice, your decision to fit or not.

 

[Dereekoo]

On Sunday we had 6mm of rain, this morning we had 2.9mm. A chimney pot might collect rain from an area of maybe 100 square mm, at a guess - maybe 1/2 a pint of water being unnecessarily poured down your chimney, and going into your home. Entirely your choice, your decision to fit or not.

I assume you mean a 100 mm square opening which would = 100cm2
Which at a depth of 6mm would mean a volume of 60cm3
1 cm3 is a ml, there are 568ml to a pint so 60cm3 =60/568 = approx one tenth of a pint

 

[stuart45]

It was never a problem years ago. The amount of water that went down was easily soaked into the parging, and dried out when the fires were going, or even air flow in the summer. A small amount of water will run down a liner though, and sit in the appliance when it's not being used.

 

[Harry Bloomfield]

I assume you mean a 100 mm square opening which would = 100cm2
Which at a depth of 6mm would mean a volume of 60cm3
1 cm3 is a ml, there are 568ml to a pint so 60cm3 =60/568 = approx one tenth of a pint

Yes, sorry - my patience was being tested

 

[catlad]

Redundant chimneys without cowls take a long time ( depending on how well they were built in the first place ) to start showing problems, A lot of old properties in Lancashire with old chimneys, were the customers have fallen into the habit of just switching on the central heating! with no cowls the chimney will be needlessly getting damp and it will start to deteriorate.
We do get a lot more rain than most area's though.

 

[Matt723]

A lot of good information here, thank you. Cowls will be installed on my 3 pots then to protect from water. One of the pot was already removed to place a small cap which apparently is a vent.

Thanks for your help!