How the wood vs gas fireplace comparison works
Both fuels are priced in different units, so the first step is to put them on the same footing: the heat your rooms actually receive. A cord of seasoned hardwood holds about 20 MMBtu of gross heat, and a therm of natural gas holds 0.1 MMBtu, so 10 therms make 1 MMBtu. If the fireplace must deliver 25 MMBtu in a season, the wood fireplace has to burn 25 ÷ 0.65 = 38.46 MMBtu of wood, because only 65% of the wood’s heat reaches the room, and the gas fireplace has to burn 25 ÷ 0.80 = 31.25 MMBtu of gas. The wood becomes 38.46 ÷ 20 = 1.9231 cords, and the gas becomes 31.25 × 10 = 312.5 therms. Price those, add the annual maintenance, and you have the annual cost; add the install price and multiply the annual cost by 10 for the decade.
At the defaults — 25 MMBtu of heat, wood $250/cord at 65% efficiency, gas $1.60/therm at 80% efficiency, installed $4,500 wood vs $3,800 gas, maintenance $200/yr wood vs $75/yr gas — the wood fuel costs 1.9231 × $250 = $480.77 and the annual wood cost is $480.77 + $200 = $680.77/yr. The gas fuel costs 312.5 × $1.60 = $500.00 and the annual gas cost is $500.00 + $75 = $575.00/yr. Gas wins the year by $105.77, and over 10 years the totals are $4,500 + 10 × $680.77 = $11,307.69 for wood against $3,800 + 10 × $575.00 = $9,550.00 for gas — gas ahead by $1,757.69.
| Wood fireplace | Gas fireplace |
|---|
| Energy in | 38.4615 MMBtu/yr | 31.25 MMBtu/yr |
| Fuel bought | 1.9231 cords | 312.5 therms |
| Fuel cost | $480.77/yr | $500.00/yr |
| Maintenance | $200.00/yr | $75.00/yr |
| Annual cost | $680.77/yr | $575.00/yr |
| Installed | $4,500.00 | $3,800.00 |
| 10-year total | $11,307.69 | $9,550.00 |
The worked example, line by line
Setup: 25 MMBtu of delivered heat; wood $250/cord at 65%; gas $1.60/therm at 80%; installed $4,500 vs $3,800; maintenance $200/yr vs $75/yr.
Line 1 — the energy each fireplace must burn. Wood: 25 ÷ 0.65 = 38.4615 MMBtu/yr. Gas: 25 ÷ 0.80 = 31.25 MMBtu/yr.
Line 2 — the fuel bought. Wood: 38.46 ÷ 20 = 1.9231 cords. Gas: 31.25 × 10 = 312.5 therms.
Line 3 — the fuel cost. Wood: 1.9231 × $250 = $480.77. Gas: 312.5 × $1.60 = $500.00.
Line 4 — the annual cost. Wood: $480.77 + $200 = $680.77/yr. Gas: $500.00 + $75 = $575.00/yr. Gas wins by $105.77/yr.
Line 5 — the 10-year totals. Wood: $4,500 + 10 × $680.77 = $11,307.69. Gas: $3,800 + 10 × $575.00 = $9,550.00. Gas ahead by $1,757.69.
Line 6 — the break-even wood price. Wood ties gas when its fuel costs $575.00 − $200 = $375.00, which at 1.9231 cords is $375.00 ÷ 1.9231 = $195.00/cord. Buy wood cheaper than that and wood wins the year.
Every branch, checked
Wood at $180/cord: the fuel costs 1.9231 × $180 = $346.15, so the annual wood cost is $546.15 — and wood wins the year by $28.85. But the 10-year totals are still $9,961.54 for wood against $9,550.00 for gas: the $700 install premium and the $125 a year of extra maintenance eat the fuel saving for almost a decade. Cheap wood wins the year, not the decade.
Gas at $2.20/therm: the gas fuel costs 312.5 × $2.20 = $687.50, so the annual gas cost rises to $762.50 and wood wins the year by $81.73. Dear gas is the wood fireplace’s best friend: every cent on the gas price widens the gap, because the gas fireplace burns 312.5 therms a season.
Demand 40 MMBtu: a bigger heating load needs 40 ÷ 0.65 = 61.54 MMBtu of wood, or 3.0769 cords costing $769.23, for an annual wood cost of $969.23; gas needs 50 MMBtu, or 500 therms costing $800.00, for an annual gas cost of $875.00. Gas still wins, by $94.23/yr — a bigger load does not flip the answer, because both fuels scale with the same demand.
Wood efficiency 75%: a better wood insert burns only 25 ÷ 0.75 = 33.33 MMBtu, or 1.6667 cords, costing $416.67 for an annual wood cost of $616.67 — but gas still wins by $41.67/yr. Efficiency helps wood a lot (it saves $64.10 a year against the default), yet the maintenance gap alone is $125 a year, so efficiency alone cannot close it.
Reverse — the wood price that ties gas: wood ties gas on annual cost when its fuel costs $575.00 − $200 = $375.00. At 1.9231 cords that is $375.00 ÷ 1.9231 = $195.00/cord. If you cut your own wood, or buy it at $150 a cord from a neighbour, wood wins easily; at the $250-a-cord delivered price, gas wins.
What the defaults assume
The model counts fuel and maintenance only: it does not count the value of your time splitting and stacking wood, the electricity a gas fireplace’s fan uses, or the cost of the wood itself if you cut it (which is free in money but not in weekends). It assumes a cord of seasoned hardwood holds 20 MMBtu of gross heat — green or softwood holds less, and a cord is a stacked measure, so the actual wood varies — and it assumes gas prices and wood prices stay flat for 10 years. It assumes both fireplaces last the full horizon and ignores resale value: a wood insert may add more to a house’s value in a rural market than a gas one. The efficiencies are for modern inserts and direct-vent units; an open-hearth wood fireplace is about 10% efficient, which would make wood lose by thousands, not hundreds. Rounding convention: money is rounded to cents and all figures are computed from unrounded values, rounded only for display.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Wood energy in | demand ÷ wood efficiency | 38.4615 MMBtu/yr of wood heat to burn. |
| Cords of wood | wood energy ÷ 20 MMBtu/cord | 1.9231 cords a season. |
| Wood fuel cost | cords × $/cord | $480.77/yr. |
| Wood annual cost | fuel + maintenance | $680.77/yr. |
| Gas energy in | demand ÷ gas efficiency | 31.25 MMBtu/yr of gas heat to burn. |
| Therms of gas | gas energy × 10 | 312.5 therms a season. |
| Gas fuel cost | therms × $/therm | $500.00/yr. |
| Gas annual cost | fuel + maintenance | $575.00/yr. |
| 10-year wood total | install + 10 × annual | $11,307.69. |
| 10-year gas total | install + 10 × annual | $9,550.00; gas ahead $1,757.69. |
| Wood $180/cord | same model, wood $180 | Fuel $346.15, annual $546.15, wood wins $28.85/yr, 10-year wood $9,961.54 vs gas $9,550.00. |
| Gas $2.20/therm | same model, gas $2.20 | Fuel $687.50, annual $762.50, wood wins $81.73/yr. |
| Demand 40 MMBtu | same model, 40 MMBtu | Wood fuel $769.23, annual $969.23; gas fuel $800.00, annual $875.00; gas wins $94.23/yr. |
| Wood efficiency 75% | same model, wood 75% | 1.6667 cords, fuel $416.67, annual $616.67, gas wins $41.67/yr. |
| Reverse: break-even wood price | (gas annual − wood maint) ÷ cords | $195.00/cord. |
Who uses this
- The homeowner replacing a dead insert: the stove shop quotes $4,500 for wood and $3,800 for gas — they learn gas is $105.77/yr cheaper to run and $1,757.69 cheaper over 10 years, so they take the gas unit and keep their weekends.
- The family with cheap local wood: a neighbour sells seasoned hardwood at $180 a cord, so their wood fuel is only $346.15 and wood wins the year by $28.85 — so they buy the wood insert and stack the savings.
- The couple on expensive gas: at $2.20 a therm their gas bill would be $762.50/yr, so wood wins by $81.73/yr — and the wood fireplace becomes the main heater, not the decoration.
- The renovator choosing a high-efficiency insert: a 75% wood insert burns only 1.6667 cords for $416.67 of fuel — they learn it still loses to gas by $41.67/yr on money, so they buy it for the heat and the look, not the savings.
Accuracy & limitations
The math is exact for the numbers you enter: the energy in is the demand divided by the efficiency, the cords are the wood energy divided by 20 MMBtu, the therms are the gas energy times 10, and the costs are those quantities times the fuel prices plus maintenance. What the model cannot do is know your wood: a cord is a stacked measure, so the actual solid wood varies, and green wood, softwood, or a cord short-stacked by a careless supplier all hold less than 20 MMBtu. It leaves out your time — splitting, stacking, hauling and sweeping are real work, and a gas fireplace asks for none of it — and it assumes prices stay flat for 10 years. It also assumes the efficiencies you enter: an open-hearth wood fireplace is about 10% efficient, which would make wood lose by thousands a year, so check whether your fireplace is an insert or an open hearth before you trust the result. For gas versus electric water heating, see gas vs electric water heater; for the water heater comparison itself, see tankless vs tank water heater.
Cite this calculatorBright Side Kit. “Wood vs Gas Fireplace: Annual Heating Cost Calculator.” brightoolbox.com, 2026. Method: wood energy in = demand ÷ wood efficiency; cords = wood energy ÷ 20 MMBtu/cord; wood fuel = cords × $/cord; gas energy in = demand ÷ gas efficiency; therms = gas energy × 10; gas fuel = therms × $/therm; annual cost = fuel + maintenance; 10-year total = install + 10 × annual cost; break-even wood price = (gas annual − wood maintenance) ÷ cords. Defaults: 25 MMBtu, wood $250/cord at 65%, gas $1.60/therm at 80%, installed $4,500 wood vs $3,800 gas, maintenance $200/yr wood vs $75/yr gas → wood energy 38.4615 MMBtu/yr, 1.9231 cords, fuel $480.77, annual $680.77/yr; gas energy 31.25 MMBtu/yr, 312.5 therms, fuel $500.00, annual $575.00/yr; gas wins $105.77/yr; 10-year wood $11,307.69 vs gas $9,550.00, gas ahead $1,757.69; wood $180/cord → fuel $346.15, annual $546.15, wood wins $28.85/yr, 10-year wood $9,961.54 vs gas $9,550.00; gas $2.20/therm → fuel $687.50, annual $762.50, wood wins $81.73/yr; demand 40 MMBtu → wood fuel $769.23, annual $969.23; gas fuel $800.00, annual $875.00, gas wins $94.23/yr; wood efficiency 75% → 1.6667 cords, fuel $416.67, annual $616.67, gas wins $41.67/yr; break-even wood price $195.00/cord.Bright Side Kit. "Wood vs Gas Fireplace: Annual Heating Cost Calculator." https://brightoolbox.com/wood-vs-gas-fireplace/ Accessed October 24, 2026.
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