Fighting The Flue Gas Condensates, The Advanced Chimney Solutions

As all exhaust gasses contain certain portion of water (in the form of steam), usually around 10%, the chimney flue has to be hotter than 60?C (which is the condensation point of the flue gas with 10% of water) in order not to condensate the gasses. But if the hot flue gas meets with cool (much cooler than 60?C) air in the upper part of the chimney, it is forced to condensate and pours back to the chimney liner. This often happens when just heating the stove. If the condensate is not neutralized (in the built-in collector with carbon absorbent) it starts to gather the sulfur and carbon oxides from the air and at the end of this chemical reaction we have got the carbon and sulfur acids that corrupt the mortar of the chimney liner and masonry of the chimney.

The carbon based condensate is often called a creosote. Creosote is usually of black color and can appear in several forms; from black powder soot (that is inflammable, can explode and produce the temperature of more than 1000?C, which is too much for any residential chimney), to numerous fragile porous forms (the glaze bubbles). The chimney corrosion usually starts in it´s upper part which is the coldest and therefor forces the combustion exhalates to condensate the most; but later, if this happens on a regular basis the acids will destruct your chimney completely.

What are you supposed to do with the flue damaged by creosote?

Well you can just accept this fact and regularly re-mason the destructed part of the chimney. If the upper part of the chimney is damaged too much, you can re-build it again, anyway, it requires your constant effort to keep the status quo. Much wiser solution is to replace the ceiling part of the chimney and the part of it that exceeds the roof with a multi-wall, metal or ceramic chimney system.

The double-wall or triple-wall chimney systems can be used for venting of all types of stoves, if the right material composition is used. They usually consist of: - the stainless steel inner liner acting as the chimney flue; - the insulation layer or more insulation layers between the inner and outer wall; - the stainless steel (or cheaper galvanised steel) outer wall. The insulation layer enables the chimney to keep it´s inner part - within the chimney liner - very hot and at the same time the outer wall stays cold or just slightly warm. This is very advantageous feature of the multi-wall chimneys as they can be used also inside the buildings with minimized fire hazard. As the flue is very hot (up to 300?C) it draws the exhalates very quickly from the chimney to the air and the condenstation effect is minimized, as the surroundings of the chimney outlet is much hotter than the condensation temperature of the combustion gas. Multi-wall chimney systems can also contain more insulation layers, e.g. insulation matting + air insulation or ceramic insulation + the air insulation and therewith achieve even better conditions for minimizing the acid condensates and creosote creation.