This varies with amount of use, the way the appliance is operated and the type and quality of fuel used. With flexible steel liners in general the 316 quality liner comes with a 10 year guarantee, 904 quality usually carries a 25 year guarantee. We suggest that where the fuel burnt is largely or exclusively fossil fuels then the higher quality 904 steel is used. This has better resistance to the acids associated with burning coal. For most appliances a Class 1 316 stainless steel liner is entirely acceptable.
Preferable to both these is the pumice system which has excellent longevity and durability together with the insulation value that exceeds that of the flexible liners. These carry only a 10 year guarantee but in our experience are very long lasting.
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