Kiln-dried vs seasoned value
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check the figures against your stove's manual, your supplier and your installer.
Short answer
Enter each supplier's price, the weight of a load and the logs' moisture, plus your stove's efficiency. The calculator works out the useful heat in each load and how much you get for each pound, with the working shown. The prices are always yours: we never fill them in.
Worked example
| You enter | Value |
|---|---|
| Kiln-dried: moisture content | 15% |
| Seasoned: moisture content | 20% |
The kiln-dried logs are drier, so they give more heat per kg. Add the load weights and prices to compare value
Show the working
- Moisture: kiln-dried 15%, seasoned 20%: the kiln-dried logs carry less water per kg
How it works
- Energy per kg (kWh/kg) = energy in oven-dry wood × (1 − moisture) − energy to dry off the water × moisture
- Useful heat per kg = energy per kg × stove efficiency; per load = per kg × the load's weight
- Useful kWh for each pound = useful heat per load ÷ the price of the load (your prices)
Compare loads by weight, not volume: a loose load and a stacked load of the same size hold different amounts of wood. Ask each supplier what a load weighs.
Moisture matters more than the label. Measure both with a meter on a freshly split face: logs at or below 20% give more heat per kg and a cleaner fire.
Assumptions and sources
The figures this calculator starts from, and where each comes from. Your stove's spec plate, your supplier and your own meter readings come first: change any figure to match.
This calculator has no built-in defaults: every figure comes from you or your product's data.
| Table | Clause | Nations | Status |
|---|---|---|---|
| Energy in firewood by moisture content Researcher to cite (e.g. Forest Research, the Biomass Energy Centre or Woodsure) | Net calorific value by moisture content: NCV = dry-wood NCV × (1 − w) − latent heat of water × w, with w the moisture content (wet basis). Brief §4 wood.js: standard formula, RtV. | UK-wide | 0/2 values entered Not yet checked against the source |
Rules of thumb and reference figures are checked against their sources before launch; anything not yet checked is marked.
FAQs
Are kiln-dried logs worth the extra?
It depends on the prices and on how dry each load really is. Drier logs give more heat per kg, so compare useful heat for your money, not price per load.
Why compare by weight, not volume?
A loose load and a stacked load of the same size hold different amounts of wood. Ask each supplier what a load weighs.
Are seasoned logs dry enough to burn?
Only if they measure at or below 20% on a freshly split face. Check with a moisture meter. See log moisture content explained.
Can I dry seasoned logs further myself?
Yes. Stack them under cover with the sides open, and measure again before you burn them. See how to season firewood.
Guides
Kiln-dried vs seasoned logs: heat per pound
Kiln-dried or seasoned logs? Compare the heat you get per pound from their moisture and your prices, not the label.