Most
modern wood heaters are attaining emission levels far below the EPA limit,
some as low as 0.9 g/k and this shows the level of commitment the manufacturers
have to their designs and manufacturing standards. Always check when buying
a heater that it complies with these standards. There should be a compliance
plate stating brand, model, serial number, efficiency rating and emission
rating (i.e. passed testing
for AS4012 and AS4013) In the past, when we were not concerned about such
things, the air inlet control allowed for almost full deprivation of air to
the firebox and this was often misused resulting in lots of smoke and creosote
build-up because the fire would smoulder not burning off the solids in emission
like it should.
These days the air is regulated so that even on the lowest setting, you will
still have flame and the unit is burning cleanly for about ten hours or more.
There is always some smoke
when the fire is first started and straight after refuelling, but during normal
combustion you should only see a heat haze coming out of the cowl.
Every time you start the fire or refuel, open the air fully for 15 to 20 mins
to burn off any moisture in the wood. Then the fire can be regulated to your
liking.
The air is fed into the firebox in such a way as to flow down the inside of
the glass door (cooler air is denser and heavier) and as it does so it keeps
the glass clean. As it heats
up, it expands and is forced upwards where it is generally injected with a
fresh supply of oxygen from the secondary air inlet. Any unburnt particles
are reignited at this point. By the time the emissions have moved forward
and around the baffle plate, they are nearly completely burned and the small
amount of residual particals are sucked into the flue and drawn upward.
Typical air and emission
flow in convective controlled combustion heater.
The main purpose of any combustion chamber design is to maximise the combustion
process thereby increasing the efficiency of the heater resulting in less
emission.
The E.P.A. regulations state that no wood heater should produce more than
4 grams of solids in emission (soot) per kilo of wood burned.
This makes them enviro-friendly and efficient and the fact that timber
is a renewable resource makes them even better.
