I'll address the inevitable concerns— do not ever burn treated lumber due to very toxic chemicals in them!! This is specifically referring to untreated softwoods (pine, ake for spruce, fir, whitewood!) that are sold at mosts box stores. They are kiln dried and burn extremely well!
Yes, basic 2x4 scraps are safe to burn unless they are treated.
While burning untreated, unpainted wood may not raise environmental red flags, it isn't good for your wood stove. Each of the processes that harvested lumber undergoes to become lumber, from transporting to milling and drying, introduces corrosive chemicals to the wood fibers.
Treated wood should not be burned in stoves, fireplaces or outdoors because toxic chemicals are produced as part of the smoke and ash and can be harmful if inhaled. It is legal to dispose of treated wood in the landfill, although it's always best to find a way to re-use it.
The wood that is unsafe is sap filled pine. The sap explodes and showers you with hot sparks. But you can still use pine or spruce or cedar, all sparky woods, if you reduce it to coals before cooking. Better hotter woods are birch, oak, ash, the hardwoods. But I would still recommend making a cooking fire first.
Redwood and spruce also fall under this category. Poplar and chestnut are smokey, alder and spruce are too quick to burn, elder and fir fires are puny, and hemlock shoots off sparks. Eucalyptus is the worst firewood for your fireplace.
As mentioned, you should avoid green or unseasoned wood due to its high moisture content. The moisture makes it difficult to ignite, resulting in more smoke and less efficient burning. Trying to burn green wood often results in a frustrating and cold night as you fight the flames to keep working.
All lumber, from the common 2x4 to specialty marine plywood, is either pressure treated or not. Pressure treated wood does last longer without rotting and resists insect damage, but it's not right for every purpose either. Not sure whether you need pressure treated wood or should avoid it for a particular use?
The disposal of treated lumber by burning has serious health and environmental risks. In fact, it's illegal to burn in all 50 states. Treated wood is also called CCA lumber. CCA is an abbreviation of Copper, Chromium and Arsenic.
Do not burn CCA-treated timber in fireplaces, barbecues, wood stoves or any wood fire. In the event of a bushfire, the ash from burnt CCA-treated timber can contain up to 10 per cent (by weight) arsenic, chromium and copper. Swallowing only a few grams of this ash can be harmful.
What Is the Ignition Temperature of Wood? Wood placed in an oven at 700°F. catches fire almost immediately. At oven temperatures of 450°-500°F., the wood gradually chars and usually ignites after several hours.
Untreated wood is the most susceptible to rot, fungi, and general weathering. It's extremely important that you use a wood preservative first. You can either use a wax enriched preservative for an all-round coating or alternatively use a wax-free preserver if you want to then use a stain or a paint on top.
Another potential surprise is cardboard and cardboard boxes: both are things you should never burn on a fire pit. Again, the ink used on cardboard boxes will release dangerous toxins when burning. However, cardboard may also cause a surge in your fire as it burns so quickly.
Never burn construction scraps of treated or painted wood in your fireplace, especially treated wood from decks or landscaping ties – this includes 2x4s, plywood, and particle board. The chemicals used can release dangerous amounts of arsenic and other very toxic compounds into your home.
So what's our formal opinion on 2 x 4 scrap lumber bits for firewood? Its fine for home use, backyard use, and local campgrounds when permitted. But because it brings up a lot of questions when moved farther or across borders, it'd be best to restrict using 2x4s to your nearby campgrounds, and call ahead.
While pine is a great and inexpensive choice for fire pits, it is best suited for kindling instead of traditional firewood logs. Pine burns extremely fast, making for a much shorter fire, even with a large stock.
Stay clear of treated wood or anything that's been painted when choosing fuel for your fire pit. These materials often contain nasty chemicals like creosote that release toxic fumes when you burn them.
More than 90 percent of all outdoor wooden structures in the United States are made with arsenic-treated lumber. Using wipe tests from 263 decks, playsets, picnic tables and sandboxes in 45 states, researchers found that arsenic levels on wood surfaces remain high for 20 years -- the entire useful life of the wood.
While some pallets constructed from untreated wood can be safely burned, many pallets are treated with pesticides, fumigants, or chemicals that prevent rotting or insect infestations. Painted pallets, those visibly contaminated, or pallets marked with the letters MB should never be burned.
Simply put: In most cases, treated wood is ideal for outdoor use; whereas untreated wood is best for indoors. This is due to the manufacturing process undergone by treated wood, which better protects it against the weather and common pests.
If you buy ordinary pressure-treated lumber from a home center, however, you'll have to wait anywhere from two to three days for the wood to dry sufficiently before you can apply a water-based semitransparent protective stain.
Some Things to Not Burn in Your Firepit
You don't want to burn treated wood, deck lumber, painted or stained wood planks, shipping palettes, or driftwood. These types of wood have usually been treated with chemicals that can be potentially dangerous and toxic to inhale.
Never leave a fire pit burning overnight.
It's unsafe and often illegal due to the risk of fire spread and legal penalties. Properly extinguish your fire pit using water, sand, or a fire snuffing lid to ensure no embers remain.
Uncured Firewood Can Lead to Creosote
If you're burning unseasoned firewood in a fireplace, a wood stove, a wood furnace, or any other wood heating appliance that utilizes a chimney, you'll quickly wind up with creosote buildup in the appliance's flue.