8.5°F. That’s the average low for January in Sioux Falls, the reference point NOAA uses for South Dakota winters, and it’s the number that decides everything else on this page: how many cords you’ll burn, which species are worth chasing, and whether a wood stove is decoration or the thing keeping your pipes from freezing. In a state where that figure holds for weeks at a stretch, seasoning and density stop being preferences and start being math.
How cold it actually gets here
An average daily minimum of 8.5°F for the coldest month, based on NOAA’s 1991-2020 Climate Normals for the Sioux Falls station, isn’t a record cold snap. It’s the typical low, night after night, for the worst stretch of winter. That distinction matters because a record low is a story you tell; an average low is the condition your house, your stove, and your woodpile actually have to survive for weeks running.
At that temperature, wood heat in South Dakota isn’t ambiance. It’s infrastructure. A house drawing on a stove or insert through a Sioux Falls winter is asking that fuel to do real work, night after night, often while outdoor temperatures sit well below freezing from November through March. Compare that to a coastal or southern climate where the coldest month rarely dips under 40°F, and the whole equation for firewood buying changes: there, a cord or two covers occasional fires. Here, running short in February isn’t inconvenient, it’s a heating failure.
What 8.5°F means for planning
This figure pushes three decisions that don’t matter as much in milder states. First, volume: you need enough wood, full stop, not a decorative rack by the porch. Second, density: a cord of light, fast-burning wood forces more loading, more waking up at 2 a.m. to feed a dying fire. Third, timing: seasoning has to start early enough that wood cut this year is actually ready to burn when the mercury drops toward that 8.5°F average, not still sweating moisture out in a woodshed.
None of this means every household in the state depends on wood as a sole heat source. Plenty use it as a supplement to propane or electric heat, and for those homes the math is gentler. But even as a supplement, an 8.5°F average low means the wood has to actually perform when it’s called on, which is where species and seasoning both start to matter more than they would somewhere the coldest month barely dips below room temperature.
Which woods are worth the effort here
Once the cold figure is set, density becomes the variable that decides how much heat a single cord actually delivers. A cord is a fixed volume, a stack measuring 4 feet by 4 feet by 8 feet, or 128 cubic feet, according to Michigan State University Extension. Fill that volume with dense wood and you’re packing more mass, and more stored energy, into the same footprint. Fill it with light wood and you’re burning through it faster for the same heat, which matters a lot at 8.5°F and barely at all somewhere mild.
MSU Extension puts the benchmark at roughly 20 million BTU per cord for well-seasoned hardwood on average, the equivalent of about 145 gallons of #2 fuel oil or 215 gallons of LP gas. That’s the number to hold onto: it’s an average across seasoned hardwood generally, not a guarantee for any specific load, since species and moisture both move it substantially in either direction.
Red oak is the one species called out specifically in the seasoning research, and it’s worth knowing why. Its tight, dense cell structure is exactly what makes it a strong overnight-burn candidate once it’s properly dried, but that same structure is what makes it slow to season in the first place. That’s a direct trade: the density you want on the coldest nights is the same property that punishes you if you try to rush the drying.
| Wood category | Heat value | Smoke | Sparks |
|---|---|---|---|
| Well-seasoned hardwood (average, incl. red oak) | ~20 million BTU/cord | Low once fully dry | Few |
| Red oak specifically | Same hardwood range, if fully seasoned | Low, but only after extended drying | Few |
| Green or unseasoned wood | Well under 20 million BTU/cord (energy lost boiling off moisture) | Heavy, plus creosote buildup | Variable, often more with sap content |
Availability on the ground in South Dakota shapes this table as much as the BTU numbers do. A dense species you can only find green, or can’t find seasoned at all, is worse to burn than a lighter wood you can actually get properly dried. That’s not a knock on any species, it’s just how seasoning works: the wood in front of you, dry, beats the wood on paper, wet.
How much wood a winter takes
There’s no honest single number for “cords per winter” in South Dakota, because that figure depends on three things that vary house to house, not just on the climate. Publishing a flat number ignores all three and sets buyers up to either run short in February or overbuy and store wood they didn’t need.
- The cold figure itself. An 8.5°F average low for the coldest month means more heating days and colder nights than a milder reference city, which raises baseline demand before anything else is considered.
- How well the house holds heat. Insulation, air sealing, window quality, and even how tightly a stove is fitted to the flue all determine how much of that generated heat actually stays inside instead of leaking out.
- Whether wood is the main heat source or a supplement. A household relying on wood exclusively burns dramatically more than one using it to take the edge off a propane or electric system on the coldest nights only.
The mechanism that makes these variables move the estimate so much is straightforward: a poorly insulated house in a hard winter can burn double what a tight, well-sealed house uses in that same 8.5°F climate. Two neighbors in Sioux Falls, same outdoor temperatures, same stove, can land on entirely different wood needs because one house leaks heat through an old attic and drafty windows while the other doesn’t. That’s why the honest answer to “how many cords” is a process, not a number: start with your climate, adjust for your house’s heat retention, adjust again for whether wood is primary or supplemental, and track actual usage through one winter to calibrate the next.
Drying wood in this climate
Seasoning matters more than species selection almost everywhere, and South Dakota’s climate doesn’t change that ranking, it changes the timeline. The target is the same regardless of location: 20 percent moisture or less, down from green wood that can run over 60 percent, according to MSU Extension. What gets you there is airflow and time working together, not sunshine, which is why wood stacked in a shaded but breezy spot dries as well as, or better than, wood baking in direct sun with no air movement underneath it.
Split, stacked wood exposed to moving air typically reaches that 20 percent threshold after one full summer of seasoning. The key word is split: rounds left whole trap moisture at the core no matter how long they sit, because the bark and the outer wood block the airflow that actually pulls water out. Stacking with gaps for air to move through, off the ground, and away from anything blocking wind is what does the actual work.
Red oak is the documented exception to that one-summer rule. Its dense cell structure that makes it such a strong overnight burner also makes it resist drying, so it needs meaningfully longer than a summer to reach 20 percent moisture, even split and stacked correctly. Treating it like any other hardwood on a fixed seasoning calendar is one of the more common ways firewood ends up burned too green.
Tie this back to the state’s winter timing and the most common local mistake becomes obvious: wood split and stacked in spring for that same winter almost never makes it to 20 percent moisture before the cold arrives. With an average low of 8.5°F showing up as early as November in a typical year, wood needs a full season, and for red oak specifically more than that, before it’s ready to earn its place in the stove. The wood burning well this January should have been split and stacked the spring before, not the one just past.