Firewood vs Natural Gas Cost Calculator

Some readers should not switch to wood. If your gas rate is $0.90 per therm and you're paying $400+ for delivered mixed hardwood in a coastal market, the calculator will tell you gas wins. That's the right answer, don't override it.

Gas also wins when your only option is an open fireplace (10–25% efficiency), when your cord supply is green or softwood, or when the chimney cleaning cost erases the fuel savings. The honest use of this calculator is to find out which case you're in, not to confirm wood is always cheaper.

New England homeowners face this directly: EIA data shows residential natural gas can be $1.80–$2.20 per therm in Massachusetts, which is where wood becomes interesting, but cord prices there also run $350–$500. Run your state's actual numbers. The state selector above pulls live EIA rates.

If you're in the stage of deciding whether to buy a wood stove, the Inflation Reduction Act changes the math. EPA-certified wood stoves at 75%+ efficiency qualify for 30% of purchase and installation cost, up to $2,000, via IRS Form 5695. This applies to tax years 2023–2032.

On a $5,000 fully installed certified stove, that's $1,500 back. On a $6,700 installed project, you hit the $2,000 cap. The credit doesn't require itemizing, it's a direct credit off your tax bill.

Competitor pages mention this credit. None show the dollar math on a real project. The stove ROI calculation: (installed cost minus credit) / annual fuel savings = payback years.

At $300 per year in fuel savings and a $3,500 install after a $1,050 credit, payback is 8.2 years on a stove that lasts 25 years.

Comparing a cord price to a therm price directly is like comparing a gallon of paint to a square foot of wall, the units don't match. The only fair comparison is cost per million BTU of heat actually delivered into your home.

Here's the arithmetic the calculator runs. Oak at $250 per cord holds about 26 MMBTU of raw heat, per the USDA Forest Products Laboratory Wood Handbook. Through a 75% efficient stove, that delivers roughly 19.5 MMBTU. Cost: $250 / 19.5 = $12.82 per MMBTU delivered.

Natural gas at $1.25 per therm holds 0.1 MMBTU per therm. Through a 90% AFUE furnace, each therm delivers 0.09 MMBTU. Cost: $1.25 / 0.09 = $13.89 per MMBTU delivered. Wood wins, but by less than most people expect.

Change the natGasTherm or cordPrice inputs above and watch which side of the comparison moves. That's the formula in motion.

The woodStoveEff input is the one most readers skip past. It shouldn't be. An open fireplace runs 10–25% efficiency.

A certified wood stove runs 65–80%. Same cord, very different heat.

For $250 per cord of oak: open fireplace at 15% efficiency delivers heat at $64 per MMBTU. Wood loses to gas at almost any gas rate. An EPA-certified stove at 75% delivers at $12.82 per MMBTU.

Wood wins at national average gas rates.

Here's a quick decision tree. Open fireplace: wood loses to gas at almost every cord price, the math doesn't work. Non-certified older stove (55–65%): wood is competitive only below $200 per cord in most markets.

EPA-certified stove (65–80%): wood beats national average gas rates below roughly $350 per cord for oak.

Change the woodStoveEff input above to match your actual equipment before trusting the output. If you don't know your stove's rating, check the nameplate on the back, EPA-certified stoves have been required to display it since 2020.

Two neighbors both paid $250 per cord. One bought white oak. One bought white pine. They did not get the same deal.

White oak holds about 26 MMBTU per cord. White pine holds about 14 MMBTU per cord, according to the USDA Forest Products Laboratory Wood Handbook. Through a 75% stove: oak delivers 19.5 MMBTU, pine delivers 10.5 MMBTU.

Same $250 cord price: oak heats at $12.82 per MMBTU delivered. Pine heats at $23.81 per MMBTU delivered. Pine is nearly twice as expensive per unit of heat, even at the same sticker price. Oak at $300 per cord ($15.38 per MMBTU) still beats pine at $250.

Use the species dropdown above to see how this changes your cost-per-MMBTU. Oak, hickory, and ash are the dense hardwoods worth the premium. Pine, spruce, and other softwoods are useful for kindling, not for primary heating math.

The natGasAFUE input on the calculator defaults to 90%. That's a modern mid-efficiency furnace. If yours was installed before 1992, it's likely running 60–70% AFUE.

A 65% AFUE furnace at $1.25 per therm actually costs you $1.25 / (0.1 × 0.65) = $19.23 per MMBTU delivered. That's not a cheap gas bill, that's a heating system losing 35 cents of every dollar you spend on fuel.

Change the natGasAFUE input to 65 above. The gas side of your comparison just got 30% more expensive, and wood probably wins by a wider margin than you thought.

This is the mechanism competitors miss. They compare raw $/therm to raw wood BTU, which favors gas on paper. The honest comparison adjusts both fuels for actual delivery efficiency.

The most useful output this calculator gives you isn't the annual cost comparison. It's the breakeven cord price, the maximum you can pay per cord and still have wood beat your gas rate.

At the calculator defaults (4 cords, oak, 75% stove, $1.25 per therm, 90% AFUE furnace), here's the full worked example:

Wood saves $83 per season at these defaults. Not a windfall. Change gas to $1.45 per therm and savings climb to $343.

Change cordPrice to $350 and savings disappear. The breakeven cord price at $1.25 per therm and 90% AFUE for oak is around $340 per cord, above that, gas wins.

Insist on the full delivered price before comparing. A $230 per cord "pickup price" becomes $320 with a $90 delivery fee. That changes which fuel wins.