Creosote buildup in woodburning stoves is a function of wood moisture content and combustion temperature.
Illustration by Fotolia/Piumadaquila
My family's sole source of heat is one woodburning stove, and living in chilly Minnesota, we obviously can't afford to go without it for long during the dead of winter. My problem is that creosote buildup occurs in my chimney at a rate that demands cleaning at least once a month. And being forced to let the system cool in January is a real hardship on my family, as you can imagine! So I'd like to do everything possible to cut down on the frequency of those “sweepings.”
The dealer who sold me the stove told me that if I burn seasoned hardwood I shouldn't have to clean more than twice a year. Other people have suggested that it's not so much what wood one burns but rather how one burns it. That is, that it's important to keep the fires hot enough to consume the creosote in the smoke. Still others suggest that the problem might be with my chimney. What I'm wondering is this: Just how much substance is there to the contention that green or softwood produces more creosote than does seasoned fuel or hardwood?
There is some truth in what all your consultants have told you. Softwoods often produce a little more creosote than do hardwoods, but not under all circumstances. However, the effect of wood type is not as important as chimney type and location, and this isn't as crucial as is how you operate your stove.
In our experiments, we've found that depending on the air setting on the test stove and the fuel moisture content, pine (a softwood) resulted in anywhere from the same amount of creosote as oak to about four times as much. And, although this is by no means a trivial difference, it is less significant when compared with the effect of the heater's air setting itself. We observed up to 48 times more creosote with a smoldering fire than with a hot flaming fire using the same fuel.
Thus, the most important and easiest way to reduce creosote buildup is to burn the fuel rather than smoke it. Smaller fuel loads and larger air settings are the key. This will require more frequent refueling, of course, but you won't burn significantly more wood to produce the same amount of heat.
Jay Shelton is the director
of Shelton Energy Research.