Seattle’s coldest month bottoms out at a mean minimum of 37.1°F, which sounds mild until you realize what that number actually demands from a furnace or a woodstove running day after day for months on end. Here’s what that figure means for your heating season, your wood pile, and your wallet.
How cold it gets, and for how long
That 37.1°F figure is the average daily low for the coldest month, not the record low and not some cherry-picked cold snap. It comes from NOAA’s 1991-2020 Climate Normals for the Seattle reference station, and it tells you something specific: this region rarely plunges into deep-freeze territory, but it also rarely lets up. The heating season here is long and mild rather than short and brutal.
That distinction matters more than most homeowners realize when they’re sizing equipment or budgeting for fuel. A place that spends two months at 10°F below zero and then warms up fast puts a short, intense demand on a heating system. Western Washington does something different: it hovers in the upper 30s and low 40s for a stretch that can run from October into April, with plenty of damp, gray days in between, which raises the question of When Does the Heating Season Start in Washington? The furnace or stove isn’t fighting an extreme, it’s grinding through a marathon.
What a mild-but-long winter does to your system
Equipment sized for occasional deep cold can actually underperform in a climate like this, because it’s built to blast through short emergencies rather than sustain a steady, moderate output for weeks at a stretch. Wood-burning households feel this directly. A stove that’s fine cycling hot and cooling off in a place with sharp cold snaps has to run longer and more evenly here, which changes how much wood you go through and how you manage the burn.
Humidity compounds it. Damp cold feels colder than the thermometer suggests, and it also affects how efficiently a chimney draws and how fast firewood picks up moisture again after it’s split and stacked. None of that shows up in the 37.1°F number by itself, but it’s the practical reality behind it.
What a cord of wood is worth here
A cord is a volume, not a weight, and that distinction is where most firewood buyers get shortchanged. The standard measurement is a stack 4 feet high, 4 feet wide, and 8 feet long: 128 cubic feet total, loosely stacked with the inevitable air gaps between splits. Two sellers can hand you the same “cord” and deliver very different amounts of actual wood, depending on how tightly it’s stacked and how big the pieces are.
What that cord delivers in heat depends heavily on species and moisture. According to Michigan State University Extension, a cord of well-seasoned hardwood puts out roughly 20 million BTU. That’s an average across dense hardwoods burned dry, and MSU frames it in terms most homeowners can actually picture: one cord is roughly equivalent to 145 gallons of #2 fuel oil, or 215 gallons of LP gas. Given a heating season that runs long here rather than hitting hard and fast, that BTU output has to be stretched across months, not weeks.
| Measurement | Value |
|---|---|
| Cord dimensions | 4 ft x 4 ft x 8 ft |
| Total volume | 128 cubic feet |
| Heat output (seasoned hardwood) | about 20 million BTU |
| Fuel oil equivalent | roughly 145 gallons of #2 fuel oil |
| LP gas equivalent | roughly 215 gallons |
Seasoning is the variable that decides whether you actually get that 20 million BTU or something far less. Wet wood spends a chunk of its potential heat just boiling off its own water before it ever warms your living room, which is why the drying process isn’t a formality, it’s the difference between a cord that carries you through a cold month and one that burns fast and hot for an hour, then leaves you feeding the stove at 2 a.m.
How long wood takes to dry in Washington
Seasoning time isn’t a fixed number you can look up once and apply everywhere. It’s climate-dependent, driven by humidity and summer heat, which is exactly why a figure that works in a dry inland state doesn’t transfer cleanly to a marine climate like western Washington. MSU Extension’s benchmark is 20 percent moisture or less before wood is ready to burn efficiently. Green, freshly cut wood can sit above 60 percent moisture, which is a massive amount of water to drive off with heat that should be warming your house instead.
Split green wood typically reaches that 20 percent mark after one full summer of seasoning, but only if it’s split and stacked properly so air can move through the pile. Wood left in rounds, or stacked too tightly against a fence or wall with no airflow, takes longer no matter what the calendar says. Red oak is a named exception in MSU’s research: its cell structure makes it dry more slowly than other hardwoods, so it needs extra time beyond a single summer to reach burnable moisture levels.
A humid summer, like the ones that show up in wetter years along Puget Sound, slows this whole process down further. Burning too soon isn’t just a matter of losing efficiency. Unseasoned wood produces more creosote as it smolders and off-gasses moisture, and that creosote builds up in the flue faster, which means more frequent chimney sweeping and a real, if often underestimated, chimney fire risk. The fix isn’t complicated: split it, stack it off the ground with room for air on all sides, cover just the top, and give it the season it needs rather than the season you want it to have.
Where to check before you buy
Everything above describes conditions at the Seattle reference station, and Washington covers a lot of ground between the coast, the Puget Sound lowlands, and the mountains and high desert to the east. Elevation and exposure shift both the cold and the drying conditions considerably, so a homeowner in a higher, drier part of the state may see faster seasoning and a harder winter than these figures suggest.
For guidance specific to your area, including which firewood species are actually available locally and any current burn restrictions, Washington State University Extension is the resource built for that job. Burn bans and air-quality restrictions in particular are set at the local level, often by county or air-quality management district, and they change from year to year depending on conditions. Checking before you stock up, not after, saves both wasted money and a wasted afternoon splitting wood you can’t legally burn on a given night.