Methodology and sources

Cord Calc turns a state's climate, a house's size and age, a wood species and a stove into cords per winter. Every figure comes from a named public source, listed below with the date it was read. Nothing is estimated by hand; where a source could not be read, the item is left out and listed under exclusions.

Sources

Method

1. Climate. A state's heating degree days are the average of NOAA's 30 annual (January–December) statewide totals for 1991-2020, base 65°F. NCEI's readme notes its degree-day files use population weights from the 2010 Census, so the figure leans toward where people live; a home in the mountains or the far north of a state sees more.
2. Heat the house needs. EIA's 2001 Residential Energy Consumption Survey reports, for homes heated mainly with natural gas, the gas burned per 1,000 heated square feet per degree day by year of construction (4.688 cubic feet for homes built 1990–2001 up to 8.784 for homes built in 1949 or before). Heat = floor area ÷ 1,000 × that figure × degree days × 1,036 Btu per cubic foot × 78%. The 78% is the federal minimum efficiency for furnaces made before November 2015; the survey's homes ran a mix of furnaces, so this is an assumption, stated so you can judge it.
3. Cords. Cords = heat × the share supplied by wood ÷ (million Btu per cord × 1,000,000 × stove efficiency). The default wood is EIA's 20 million Btu cord; species values come from Kentucky's table where it lists the species (it states the moisture basis) and otherwise from Utah State's. The default stove efficiency, 74%, is the median of the 13 higher-heating-value efficiencies the listed makers publish. Face cords = cords × 3 (16-inch pieces, CMHC).
4. Cold-night heat. Heat ÷ (24 × degree days) gives the house's heat loss per degree; times (65°F − the outdoor temperature) gives the hourly heat on that night. It is an average-based estimate, not a room-by-room heat-loss calculation.
5. Stove fit. A stove is listed for a floor area when its maker's published heating area includes it ("up to" ratings start at zero). Makers define output differently (maximum, top of the EPA test range, or constant output on High); each page names the basis.
6. Cost. Cords × price. Only dated prices published by a state agency are shown; elsewhere you enter your own.

The engine is one file of pure functions, /js/cord.js, used both to build the pages and by the calculator in your browser. Its tests reproduce published figures from the sources: Utah State's "% of green ash" column, Drolet's printed kW conversions, Maine's dollars per million Btu, and New Hampshire's 30-year average from NOAA's annual values.

Exclusions and gaps

• Dogwood: USU lists its heat per cord as the word "High", not a number.
• Poplar: USU lists its heat per cord as the word "Low", not a number.
• Maple, Other (USU): A mixed group of maples other than silver maple; not one species, so it has no page. Its figure (25.5 million Btu) is left out of the comparisons.
• Alaska: The Climate at a Glance statewide degree-day series for Alaska could not be fetched (request error).
• Hawaii: NOAA's statewide climate-division series do not cover Hawaii.
• Englander (englanderstoves.com): The site's robots.txt does not allow the page to be fetched, so no rating could be read from the maker.
• Vermont Castings (vermontcastings.com): The site's robots.txt does not allow the page to be fetched, so no rating could be read from the maker.
• Jøtul F 35, F 445, F 500 V3, F 602 V3: The product pages publish a heating area (up to 1,200, 1,600, 2,300 and 800 sq ft) but label maximum output with an inconsistent unit (for example 70000 marked kW) and give no firebox volume, so no page is built.
• Woodstock Palladian 202: Publishes the same ratings as the Keystone 204, so it is listed on that page.
• Vermont: The Department of Public Service fuel price reports that listed cord wood stopped in 2016; a ten-year-old price is not shown.
• Massachusetts: The DOER heating fuel price page lists oil and propane only.
• Every other state: No dated cord price from a state agriculture or energy office was found.
• ZIP-level degree days: not used; the state average stands in for every address in the state.
• Insulation: modelled only through the year a house was built (the survey's grouping), not by measured insulation levels.

Estimates for planning only. A real house's wood use depends on its insulation, air leaks, layout, the thermostat and the weather; stove installation must follow the maker's manual and local code. Data version 2026-10-20.