I though those nice spirally things were a type of wind turbine meant to 
draw air out of the pipe/building.  I thought they were designed to be 
turned in one direction by the wind and that, once spinning, the turbine 
would create a vacuum in the pipe.  I thought it was mainly passive 
ventilation like you would seek to cool an attic, etc.  I wouldn't think 
it would be used on a stove or plumbing vent as I don't think you want 
or need to artificially draw large amounts of air through the vent.

Sealed to the john until the wind stops,
T. Gale



[log in to unmask] wrote:

> ... on stovepipe vents.  They spin around when the hot air or whatever 
> is coming out.  I recognize that they are more or less weathertight.  
> But are they designed to spin just diagnostically, to know when the air 
> is moving and when not?  I like the idea, but it seems like a lot of 
> effort just to make sure the air is moving.  
>  
> Christopher
> -- To terminate puerile preservation prattling among pals and the 
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--
To terminate puerile preservation prattling among pals and the
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