You should try to see a top of the range gasiffier boiler running, they have lamba sensors ( as in car exhaust systems) and automatic adjustment of the primary and secondary air ratios and volumes to minimize smoke and emissions. You'd see no visible emissions other than the heat haze.
Most 'exempt' solid-fuel appliances are obviously less complicated but are regarded as smokeless for the purposes of the smoke control legislation.
Yeah... 2003 I think, which means there are an awful lot of decks etc. still out there that people might be tempted to cut up and burn when they reach end of life.
People in this area of the US seem pretty clued-up about not burning treated stuff, but I suspect that's not the case country-wide.
cheers
Jules
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