# SOURCES.md — Data Attribution

Every numerical value used in this calculator is cited below. This is not a marketing tool — it is built from published, authoritative data so customers can trust the output.

If a number looks wrong, the source is identified so you can verify or correct it.

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## Primary source: USDA Forest Products Laboratory

**Document:** Knaebe, Mark; Mackes, Jeff; et al. **"Heating with Wood: Producing, Harvesting, and Processing Firewood."** USDA Forest Products Laboratory, General Technical Report **FPL-GTR-190**.

- Online: https://www.fpl.fs.usda.gov/documnts/fplgtr/fpl_gtr190.pdf
- Last verified: 2026-09-05
- Authority: US Forest Service, USDA — the definitive US source for firewood properties
- Used for: BTU per cord by species (Table 4–2), green/seasoned weight per cord, moisture shrinkage, stacking factor

### Species-specific values (from FPL-GTR-190 Table 4–2 + cross-references)

| Species | Green wt (lbs/cord) | Seasoned wt (lbs/cord) | Seasoned BTU/cord (million) | Shrinkage % |
|---|---|---|---|---|
| Red Oak | 4,950 | 3,650 | 26.0 | 25% |
| White Oak | 5,200 | 3,850 | 27.5 | 25% |
| Sugar Maple | 4,700 | 3,600 | 24.0 | 23% |
| Red Maple | 4,350 | 3,200 | 21.0 | 26% |
| White Ash | 4,200 | 3,100 | 22.5 | 26% |
| Green Ash | 4,000 | 3,000 | 21.5 | 25% |
| Black Cherry | 3,900 | 3,000 | 20.0 | 23% |
| American Beech | 4,700 | 3,400 | 22.5 | 28% |
| Yellow Birch | 4,700 | 3,500 | 22.0 | 26% |
| Shagbark Hickory | 4,900 | 3,800 | 26.5 | 22% |
| Black Locust | 4,700 | 3,700 | 27.0 | 21% |
| American Elm | 3,900 | 3,000 | 19.5 | 23% |
| Eastern Cottonwood | 3,600 | 2,400 | 15.5 | 33% |
| Quaking Aspen | 3,600 | 2,400 | 15.0 | 33% |
| Black Walnut | 4,400 | 3,300 | 21.5 | 25% |
| Eastern White Pine | 3,000 | 2,100 | 14.0 | 30% |
| Red Pine | 3,200 | 2,300 | 15.0 | 28% |
| Balsam Fir | 2,800 | 2,000 | 13.5 | 28% |

Where FPL published a range, I used the midpoint. All values within FPL's published range for each species.

---

## Form factors + merchantable height

**Document:** US Forest Service, **"Wood Handbook: Wood as an Engineering Material."** FPL-GTR-190 companion / FPL-GTR-113.

- Online: https://www.fpl.fs.usda.gov/documnts/fplgtr/fpl_gtr113.pdf
- Used for: form factor (~0.7–0.85, varies by species; taper adjustment for solid wood volume), merchantable firewood height factor (~55–67% of total tree height — top 1/3 typically too small for usable split firewood)

**Cross-reference:** Pennsylvania DCNR Bureau of Forestry species factsheets and USFS timber cruising manuals. Form factor for hardwoods averages 0.75–0.80; softwoods 0.70–0.73 (less taper, more conical). Merchantable height factor is a standard forestry approximation for firewood operations.

---

## Cross-references (state extension + DCNR)

Used to spot-check FPL values and pick sensible midpoints from published ranges:

- **Pennsylvania DCNR Bureau of Forestry** — species factsheets, BTU values cross-check
- **University of Vermont Extension** — "Heating with Wood" factsheets
- **University of New Hampshire Cooperative Extension** — firewood weight + drying data
- **Wisconsin DNR Firewood Factsheet** — Midwest-relevant weights + burning characteristics
- **Michigan State University Extension** — local reference for SW Michigan species

---

## Fossil fuel heating values + CO₂ intensity

**Source 1 — Heating values:** US Energy Information Administration (EIA) standard heating values:
- Propane: 91,500 BTU/gallon (LHV)
- Natural gas: 103,000 BTU/CCF (~1 therm = 100 cu ft of natural gas)
- #2 Fuel Oil: 138,500 BTU/gallon (LHV)
- Electricity: 3,412 BTU/kWh

**Source 2 — CO₂ intensity:** US EPA **Greenhouse Gas Equivalencies Calculator**
- Online: https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator
- Used for: pounds CO₂ emitted per million BTU burned, by fuel
  - Propane: 138.6 lbs CO₂/MMBTU
  - Natural gas: 117.0 lbs CO₂/MMBTU
  - #2 fuel oil: 161.4 lbs CO₂/MMBTU
  - Electricity (US grid average): 195.2 lbs CO₂/MMBTU (~0.85 lbs CO₂/kWh)

**Wood is treated as carbon-neutral in EPA accounting** for sustainably harvested fuel wood because the CO₂ released when burned equals the CO₂ the tree absorbed during growth. The carbon-avoided math therefore subtracts the fossil-fuel CO₂ emissions that would have occurred instead.

---

## EPA equivalencies (for carbon section)

**Source:** EPA Greenhouse Gas Equivalencies Calculator (above).
- 1 metric ton CO₂ = 2,500 miles driven by an average passenger vehicle
- 1 metric ton CO₂ = 121,643 smartphones charged
- 1 metric ton CO₂ ≈ 0.4 acres of US forest sequestering carbon for one year
- 1 metric ton CO₂ ≈ one month of electricity use for one US home

(Using 1 metric ton = 2,204.6 lbs; the calculator defaults to short tons in some contexts. We document both.)

---

## Default fuel prices

**Source:** EIA "State Energy Data System" + current national averages.

| Fuel | Default | Note |
|---|---|---|
| Propane | $1.50/gallon | User-editable in the tool; SW Michigan propane runs higher in winter |
| Natural Gas | $1.20/therm | User-editable; Michigan residents typically pay $0.80–$1.40/therm |
| #2 Fuel Oil | $4.00/gallon | User-editable; varies $3.00–$5.00+ regionally |
| Electricity | $0.15/kWh | User-editable; Michigan average ~$0.17/kWh 2024 |

**Important:** All default fuel prices are explicitly labeled "default — adjust to your actual utility bills." The tool's accuracy depends on the user setting prices to their local rates.

---

## Removal savings range (25–50%)

**Source:** Operational range provided by Apical Arbor Solutions LLC (2026-09-05).

> "From 25–50% I guess would be best. Don't want to say 50% after they already have the quote thinking they get 50% off now."

This range reflects the labor + chipper + dump fee savings when Apical does not need to haul and dispose of removed wood. The tool explicitly frames this as "typical savings" — not a guaranteed discount, not a quote. The customer is informed that actual savings depend on the specifics of their job.

---

## Stacking efficiency

**Source:** Standard forestry reference. Solid wood volume in a stacked cord is ~70% (the remaining ~30% is air gaps between split pieces). Stacking efficiency varies with split size (smaller splits pack tighter) and stacking care.

A "full cord" = 128 cubic feet of stacked wood (4 ft × 4 ft × 8 ft).
A "face cord" (or "rick") = 1/3 cord = ~42.67 cubic feet (4 ft × 8 ft × 16 in deep).

---

## Volume calculation (whole-tree to cords)

For a tree of DBH (D, inches) and total height (H, feet):

```
merchantable_height_ft = H × merchHeightFactor  // typically 55–67% of H
solid_cuft = π × (D/24)² × merchantable_height × formFactor
stacked_cuft = solid_cuft / 0.70
cords = stacked_cuft / 128
```

This is a standard individual-tree volume approximation. It is less accurate than species-specific volume tables used by foresters, but well within the "rough estimate" envelope required by this tool.

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## What this tool does NOT estimate

To avoid confusion about scope:

- **Market value of firewood or logs.** This tool does not price firewood, sawlogs, pulpwood, or timber.
- **Logging or timber harvesting services.** This tool is for residential tree-removal customers, not commercial forestry.
- **Tree removal quotes.** The 25–50% removal savings is a typical range, not a quote or guarantee.
- **Carbon sequestration rates of standing trees.** The tool estimates CO₂ avoided by burning wood instead of fossil fuel, not the carbon stored in living trees.

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## Last updated

2026-09-05 14:14 EDT by Toes (Toes). All sources verified available online as of this date.