Berlin wrote:Stainless liner would be the first thing I'd get rid of. Second get rid of the caps. The steel caps rust causing those stains AND anything in the flue gas such as creosote from wood or iron flyash from coal will collect on the crown and the caps thus washing down the sides of the stack with rain. If you feel that you absolutely just have to have some form of cap on your stack, go with a stone/masonry cap as others have suggested. When I build a chimney, I don't use ANY cap.
well... nothing ive seen beats a Terra Cotta flu (though no fireplace shop will admit that because seemingly the whole country is on some kind of crusade to sell stainless liners for crazy money (they even have home inspectors and building officials thinking this way)
Ive seen a tarra cotta last 100 years+++ and the only damage i ever see is caused by ice build up in a joint (something that will never happen if your burning coal through the winter OR have a nice stone cap made for it). stainless on the other hand ive seen do some seriously funky stuff when mixed with conflicting metals, gases, water, air, soot, etc. and you would think stainless steel would be able to take anything (that is not the case because in the wrong environment the stuff will disintegrate before your very eyes)
When some kid half my age at a fireplace shop told me..."sir, your tarra cotta flu needs to be lined in stainless today, your way is outdated and illegal" ... I told him "your crazy and in 10 years when that stainless rots or turns white/purple and disintegrates from electrolysis he can re-build my flu in solid bronze right"?
As i said...when building or planning your cap give yourself plenty of space between the top of flu and bottom of cap (hell make it 16" if you want), if your doing a stone cap your going to be covering the entiire top area of the chimney (not just the flu itself) so you could be 2' over and it will still stop most any the rain from getting in and this will better prevent "wash down" of soot.