posted 1 year ago
When I started living in a home with a conventional wood stove, one of the first instructions stressed to me was to only burn hardwood, because softwood produced too much creosote and was therefore a danger to safety of the system. Creosote build up would make a chimney fire more likely. Apparently, chimney fires are a bad thing.
When I started experiencing the Rocket Mass Heaters at Wheaton Labs, I quickly noticed most of the wood supply was softwood. I quickly learned that the firebox burnt so hot that creosote build up was not a concern. All particles are burnt in the chamber and don't have the opportunity to collect later in the system. They are turned into greater energy production instead of being emitted as pollution. This has been described as having a chimney fire constantly inside the combustion chamber. Apparently, chimney fires are a good thing.
All of the mature trees around me are pines, so firewood I prepared has been all softwood. However, in attending to the variety of tasks associated with homesteading, only so much wood was prepared. To make it through the winter will require buying more firewood. Everything being advertised nearby is hardwood. This is unfortunate as softwood generally sells for less when available.
I don't recall encountering much discussion of strategies involved with burning hardwood. I've heard softwood described as burning hot and fast in comparison. For the conventional insulated home this is ideal for heating up a mass that provides sufficient heat for long after a burn. The only mention of hardwood I've known was for Jamboree experiments like the kiln, where the most dense wood (black locust in this case) was desired to produce maximum temperatures.
What about a situation like the tipi on the lab? I only spent a couple of days there while working in the boot camp.
With the fire burning, everything from your knees up is toasty warm from the radiant heat. Once the fire goes out, it cools off very fast. This might be different if it were being run on a regular schedule such that the mass retains heat between firing. Seems to me in general keeping a longer, lower burn would be desirable to prolong the radiant heat regardless.
The current situation in my Yurpi (yurt/tipi hybrid) is a bit in between. I have everything insulated with quilts and blankets so it retains more ambient heat, but as soon as the fire cools down the temperature change is felt immediately. I lack the containment element of the WL tipi bench, so not sure how much a high perimeter helps.
I bought a half face cord of maple to see how it burns. I haven't done enough clock watching to get a feel for difference in length of burns. The one definite difference has been that, when I keep the maple fed in the firebox, temperatures through the system go much higher. Previously the exhaust stack would approach 300*F when I would max out the firebox with pine to cook with. Just trying to run a healthy fire with the maple had it spike over 350* when I happened to glance at it. Items on the radiant barrel also were experiencing greater heat.
With my undersized mass, burning this hot is just a waste of fuel. When I try to keep just one or two sticks of maple going, they tend to easily peter out to standing coals before completely burning. I've switched to a mix of keeping one or two pine pieces with the one or two maples to give a consistently full but lower fire going. If I see active flames coming off of the sticks, hearing the rocket effect with no smokeback, is that enough to tell that the combustion chamber is becoming hot enough for a full burn, or how is this checked?
So my main observation is that the 'quicker, hotter burn' from softwood doesn't always manifest that way with the temps. Does that refer to the softwood becoming hotter faster?
Anyone else have observations/advice for when/how to use different wood?
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