Cords Per Year

How much firewood your house burns in a year, from things you already know. It is a ballpark by design, and the receipt at the bottom shows every step.

1 · Climate

Where the house is

LatitudeLong-press your house in a maps app to copy coordinates.Longitude

Elevation, ft (optional)My spot vs. the nearest townOverride: heating degree-days, base 65 °F (optional)

Blended from Santa Rosa, CA (10 mi), Napa, CA (35 mi), Ukiah, CA (50 mi), San Francisco, CA (55 mi). Elevation used: 300 ft. That gives about 3,291 heating degree-days at base 65 °F.

2 · The house

What the heat has to get through

Enter the floor area you actually keep warm with wood.

Heated floor area, sq ftStoriesCeilingFootprint shapeExposed wallsAmount of glassBuilt or last insulatedChoosing an era fills in the five fields below.Wall insulationAttic or roof insulationFloor insulationWindowsAir leakageFoundationWind exposure

3 · Comfort

How warm you keep it

People, appliances and winter sun heat the house for free; the model subtracts that before counting a degree-day.

Daytime temperature where you sit, °FOvernight / away temperature, °FHours per day at the lower settingPeople usually homeAppliances, lights, electronicsWinter sun on the houseHeat distribution

4 · The wood

What's in the pile

SpeciesSeasoning

5 · The stove

How the heat gets into the room

ApplianceHow you burnShare of the heating that wood provides: 100%

Heat loss rate by path, 588 BTU per hour per °F

Walls105 · 18%
Roof70 · 12%
Floor100 · 17%
Glass140 · 24%
Air leaks173 · 29%

The receipt

Heat loss rate: the house shell: 1,322 ft² of wall, 240 ft² of glass, 16,000 ft³ of air; 588 BTU/h·°F
Effective thermostat: 64.0 °F
Free heat: people, appliances and sun: 3,333 BTU/h; 5.7 °F
Balance point: outside temperature below which the stove has to run; 58.3 °F
Degree-days: below the balance point, summed over the year; 1,732 °F·days
Heat the stove must deliver: = UA × degree-days × 24 h; 24.4 MBTU
Useful heat per cord: Pacific madrone 30.9 MBTU × 72% stove × 1.00 moisture × 0.92 burn habits; 20.5 MBTU
Full cords (4 × 4 × 8 ft): ≈ 3.6 face cords of 16-inch wood · ≈ 2.7 tons; 1.2

Cords by month

Jul

Aug

Sep

Oct

0.2

Nov

0.3

Dec

0.2

Jan

0.2

Feb

0.1

Mar

0.1

Apr

May

Jun

The same heat, if it came from somewhere else

257

therms of gas

95% furnace

297

gallons of propane

90% furnace

2,557

kWh

heat pump, COP 2.8

7,160

kWh

electric resistance

Reality check

Cords you actually burned last season (optional)

What this does and doesn't account for

Heat demand = heat-loss rate × degree-days below the balance point × 24 h. The balance point is your effective thermostat setting minus the free heat from people, appliances and sun, divided by the loss rate (the variable-base degree-day method).
Degree-days at any base temperature are estimated from monthly mean temperatures with the Erbs–Klein–Beckman method, which accounts for day-to-day swings. Monthly means come from the four nearest reference climates, weighted by distance and corrected 3.5 °F per 1,000 ft of elevation.
Wall, roof and floor U-values include framing, air films and sheathing, so "R-13" walls behave like the R-10 or so they really are. Crawlspaces and basements get credit for being warmer than outdoors.
Air leakage is modeled as natural air changes per hour × house volume × 0.018 BTU per ft³·°F, scaled by wind exposure. In old houses this is usually the biggest single path.
Moisture: wetter wood loses heat to evaporation and burns less completely; green wood lands about 20% behind dry in this model.
Stove efficiencies are typical higher-heating-value figures; the burn-habit factor covers the gap between a lab test and a real winter.
Not modeled: thermal mass, humidity, duct or chimney losses beyond the efficiency figure, how full your cords really are (a "cord" from a seller varies by 20% or more), bark and rot, startup fires in shoulder seasons, and microclimates finer than the offset above. Treat the range as the honest answer and the single number as the center of it.