In case anyone is interested…..
For the past number of winters, we have had an 18 inch double skin chimney stack with a Cooley hat fitted. We have also been plagued by ‘brown fluids’ dripping off the Cooley had and staining the roof – it’s almost impossible to remove the staining.
About 6 weeks or so ago, the Cooley hat got knocked off the roof and lost into the depths of the Grand Union. Since loosing the hat, we have had no more problems with the ‘brown fluids’. It would appear that the Cooley hat has been doing more harm than good and we will not be replacing it.