Portland’s coldest month averages a 36.2°F daily low, a number that sounds mild until you realize what it means for a furnace: months of steady, grinding demand rather than a few brutal spikes. Here’s what that translates to for heating bills, wood supply, and equipment choices around the state.
How cold it gets, and for how long
NOAA’s 1991-2020 climate normals put the coldest month’s average daily minimum at 36.2°F for the Portland reference station. That’s not a record low and it’s not a monthly average, it’s the typical overnight floor during the coldest stretch of the year. And 36.2°F sits close enough to freezing that a heating system in western Oregon isn’t fighting deep cold so much as it’s fighting duration.
That distinction matters more than it sounds like it should. A furnace in a place where January nights drop to 5°F cycles hard for a shorter window, then largely rests. A furnace here runs at moderate output for a much longer stretch, because the air rarely warms enough during the day to let the house coast. The heating season in the Willamette Valley routinely runs from October into April, sometimes longer at higher elevations or along the coast where damp air holds the chill.
Why the “mild” number still adds up
A 36.2°F average minimum means frost is common but hard freezes are not the norm in the valley floor. Pipes need protection on the coldest nights, but the bigger cost driver is the sheer number of days the system has to run at all. Six months of low-grade demand can rack up more total energy use than two months of intense cold, especially in older homes with weak insulation or single-pane windows that leak heat all day long.
That’s the case for treating Oregon winters as a marathon problem rather than a sprint. Sealing drafts, insulating attics, and keeping a wood stove or heat pump running efficiently over a long season pays off more than bracing for a single cold snap that, statistically, may not even arrive.
What a cord of wood is worth here
A cord is a volume, not a weight, and that single fact is where most firewood buyers get shortchanged. The standard measure is a stack 4 feet high, 4 feet wide, and 8 feet long, 128 cubic feet total. Nobody delivers wood that geometrically perfect, so the real question is always how tightly it’s stacked and how dense the species is, since denser wood packs more burnable mass into that same 128 cubic feet.
Michigan State University Extension puts a well-seasoned cord of hardwood at about 20 million BTU. To make that number mean something at home, MSU frames it against fuel oil and propane: one cord is roughly equivalent to 145 gallons of #2 fuel oil or 215 gallons of LP gas. That’s a meaningful chunk of a heating season for a wood stove doing steady work through an Oregon winter that, per the numbers above, tends to run long rather than brutally cold.
| Measurement | Value |
|---|---|
| Cord dimensions | 4 ft x 4 ft x 8 ft |
| Total volume | 128 cubic feet |
| Heat content (seasoned hardwood) | about 20 million BTU |
| Fuel oil equivalent | roughly 145 gallons of #2 fuel oil |
| Propane equivalent | roughly 215 gallons of LP gas |
None of that holds if the wood hasn’t dried out first. MSU is blunt about the mechanism: wood needs to burn at 20 percent moisture or less, while green, freshly cut wood can be over 60 percent water by weight. Every bit of that water has to boil off before the wood releases usable heat, which means a green cord doesn’t deliver anywhere close to 20 million BTU, no matter how big the stack looks in the driveway.
How long wood takes to dry in Oregon
Seasoning time isn’t a fixed number stamped on every species everywhere, it depends on climate, and Oregon’s damp shoulder seasons slow the process compared to drier inland regions. MSU’s general guidance is that split, stacked green wood usually reaches that 20 percent moisture target after one full summer of air moving through the pile, the key word being split and stacked, not left in rounds where the bark seals moisture in.
Western Oregon’s wet springs and cool, humid summers relative to arid climates mean wood doesn’t dry as fast as it would in, say, a high desert region. Stacking wood off the ground, in a single row with sun and wind exposure, and covering just the top rather than wrapping the whole pile in tarp, all help air actually reach the wood instead of trapping the humidity that Oregon’s climate already supplies plenty of.
MSU also flags red oak by name as an exception that takes longer than most species to season, because of how its cell structure holds water. Anyone burning red oak, or any dense hardwood, should treat “one summer” as a floor, not a guarantee, and check the wood’s actual moisture rather than trusting the calendar.
Burning before wood is ready doesn’t just mean a weaker fire. The moisture trapped inside has to boil off using heat the fire is producing, which lowers the flame temperature and pushes more unburned compounds up the flue as creosote. That creosote buildup is what turns a normal chimney into one that needs sweeping well ahead of schedule, and in the worst cases, it’s a fire hazard. None of this is really about wasted wood, either, it’s about a stove working harder to deliver less heat, night after night, through a season that already runs long by Oregon’s own climate numbers.
Where to check before you buy
Oregon stretches from coastal fog to high desert to alpine elevation in the Cascades, and the Portland-based figures above describe one reference point, not the whole state. A homeowner in Bend or up in the Cascade foothills is working with a different climate than someone in the Willamette Valley, and that changes both drying time and which species are locally available and affordable.
The Oregon State University Extension Service is the resource built for exactly this kind of local variation, covering species availability by region and any seasonal burn restrictions tied to air quality. Those burn rules are set at the local level, often by county or air quality district, and they change from year to year depending on conditions, so a restriction that applied last winter isn’t guaranteed to apply this one. Checking before stocking up, rather than assuming last year’s rules still hold, is the difference between a stove that’s ready when the cold settles in and one that isn’t.