Last week, the Otago Regional Council decided not to support a staff suggestion to pay for 100 solid fuel burners in towns with poor air quality and is still considering its final options.
But Dunedin chimney sweep Krystal Barna said new fires were being ruined — and were putting more dirty particulates into the air — when people ignored the instructions.
"The issue is that wood fires only run cleanly when they are burnt with soft wood. There is a label, sometimes two, on 90% of all fires installed in the last 20 years that clearly states ‘burn only soft wood’," she said.
"This is ignored and traditional hardwoods are still being burnt, which means the fire burns way outside of its tested emission scores."
Soft woods were pine, Oregon and larch. They were usually an evergreen with needles or combs.
Hardwoods were trees such as macrocarpa, old Man pine and the most popular, blue gum. They were being used incorrectly.
She said most native New Zealand trees had all the qualities of hardwood — they were dense, long-burning and full of solid oil.
"The oil, it makes the wood burn extremely hot, which means that people turn their fire down too soon, so they do not burn it in a clean way."
New fires were designed to run with an increased airflow, so particulates and combustibles in the wood and smoke burned before they exited the flue, she said.
But people had their fires so hot they turned down the airflow too soon, so secondary combustion did not occur and the particulates did not all burn, ending up going up the chimney.
"The other thing with hardwood is that it tends to come in much bigger pieces, so, again, people are overloading their fire with more fuel, running it on lower, which then just contributes to that whole smouldering situation.
"You’re meant to run them more like a charcoal barbecue with a nice big, deep base of wood coals. But because the hardwoods are dense, they don’t break down into that charcoal base, so the fire doesn’t stay hot constantly."
Fires were not supposed to be "set and forget".
"You do need tools that alter the airflow, so ideally when a fire has just started, you want to be giving it as much air as possible so that it gets everything going and the blue’s glowing and it builds up that temperature within the fire.
"It’s not about more flame. That’s not the way that fires should work any more. They’re a convection heater, not a radiant heater, so more flame does not necessarily mean you’re running it better."
Comparing a modern wood burner with an old open fire was a waste of time as they were very different, and should not be used the same when it came to adding wood.
No fire should be producing a heat which led people taking clothes off as it was too hot.
"People are paying top dollar for blue gum and they are not using it properly."
