Odsox wrote:GeorgeSalt wrote:Standard cap for a woodburner installation in the UK is a simple (and cheap) zinc cap with birdmesh round the sides
That's exactly what I have, although mine is stainless steel.
However, the only reason I got one was to stop the wind roaring, it literally made it difficult to hold a conversation or listen to TV in stormy weather. Before that it was just a standard open pot and although logic says that rain will pour down the chimney, I never noticed any problems with damp or wet. I think the soot absorbs the raindrops and the updraft dries the soot.
It was open for several years without problem, so I'm not sure you actually need a cowl at all Mal.
Yes, the dinner plate on a bird cage design is ideal to stop rain but as GS says, the rain nearly always just soaks in and evaporates. Sometimes you have problems lighting the fire or the fire will smoke on a cold wet day because of a column of cold wet air that wants to sink is sitting in the flue. If you prime or preheat the flue, by setting light to a few sheets of twisted newspaper for example, you get the air moving in the right direction.
Make sure you have clear air bricks or if not a window cracked open a tiny weeny bit to allow the chimney to draw. In old draughty houses depressurization wasn't a problem but with modern houses tight as a drum and with extractor fans going the flue can't find enough air and can smoke.