|Wood Burning Emission Comparisons
by Norbert Senf*
The worst offenders, are old technology woodstoves, and in particular outdoor boilers.
An outdoor boiler can give you roughly 100 g/kg of particulate emissions, most of which will be tar.
That's 100 grams of tar per kilogram of wood burned, or roughly 10% of the weight of what you are burning.
A masonry heater properly operated is the cleanest way to burn cordwood, and is in the same emissions range as a pellet stove, roughly 1 g/kg of particulates. Furthermore, the particulates are almost all soot (carbon), with very little proportion of tar (and PAH).
So it is not inconceivable that the ratio between best to worst when it comes to PAH emissions from wood burning is on the order of 1000:1. That's burning the same piece of wood, in two different ways.
It is not correct to say that wood is a dirty fuel. Depends on how you burn it. It is potentially very clean, since it has no sulfur, very low ash, and is nearly carbon neutral. I like the fact that it, literally, grows on trees. You don't need to bring it over from Saudi Arabia in a tanker, or from our Canadian tar sands.
Modern EPA certified woodstoves are on the clean end of the spectrum in the 2 - 10 g/kg range, depending on how you burn them.
Even with an old technology woodstove, you can burn it clean if you know what you are doing (no smoldering fires).
With the old outdoor boilers, that is impossible to do. They have a water cooled firebox, which is basically how you would design a device to produce creosote from wood, assuming you'd want to.
*Norbert Senf is the chairman of the Masonry Heater Association technical committee.
Some Wood Burning Emission Links of interest from the MHA website:
Masonry Heater Association Technical Information Archive
Wood Boilers Lower Expenses, but Raise Concerns on Smoke