According to one manufacturer it cost about $200 to get a stove ul approved and EPA certified. This is from an article posted on Mother earth dated some time in the mid 90’s Years later using the same certified manufacturing approved technique, that cost has to be considerably less. I do not know how long a certification last or how often they have before re-certification. Maybe some can goggle and post that info. It would be interesting I have to find the post where I outlined Warnock Hersey’s testing routine. Hopefully I saved that somewhere. I do remember the check the firebox capacities using 2/4’s. I wonder what cost is factored in to every stove sale today?