While not technically a hardwood, fir burns like one.
In-game description

Fir firewood is a material in The Long Dark.

It is a type of fuel source for a fire, and is also used to repair heavy hammers.

Fir firewood has an estimated fire duration of 1 hour and 30 minutes, so, with 90 min/kg it has a worse burning time per weight than cedar firewood, which gives 120 min/kg. 

Fire firewood can be harvested from fir tree limbs using a hatchet or hacksaw. A small fir limb will give 3 pieces of fir, and a large fir limb will give 4. Fir firewood can also be found inside some buildings as loot.

Fire Starting
Starters Cardboard matchesFirestrikerMagnifying lensWood matches
Tinder Birch barkCat tail headTinder plugCashNewsprintNewsprint rollStack of papers
Fuel BookCedar firewoodCoalFir firewoodFirelogReclaimed woodStick
Accelerant AccelerantLantern fuel
Hides Black bearDeerMooseRabbitWolf
Other Crow featherCured leatherGut
Medicinal Old man's beard lichenRose hipReishi mushroom
Sapling Birch saplingMaple sapling
Wood Reclaimed woodStick
Miscellaneous Arrow shaftArrowheadClothScrap metal