I've been noticing that sometimes there's little white whisps coming from the chimney top and other days it's much more. Tonight I loaded up my boiler when I kicked the fan on I noticed a big plume of white "smoke" coming from the chimney. Its a pretty foggy night tonight so I'm wondering if that's part of it or not. The "smoke" in question seems to rise from the chimney then the cloud grows in size the further from the chimney it gets. Is this smoke or stream? It's always pure white in color.