7 Types of Wood You Should Never Burn: Poisonous / Toxic Firewood

Homesteaders have many reasons for doing what they do. Commonly, they express a desire to reduce their carbon footprint and life self-sufficiently. Sourcing your own free firewood from downed trees, dead trees, and local sources can both reduce your carbon footprint and allow you to live self-sufficiently.

Related: Read my guide about Everything you need to know about the different Husqvarna chainsaw models

However, there are some sources of wood that you should be wary of. Certain kinds of wood should never be burned inside. Some kinds might suffice for an outdoor bonfire, but they shouldn’t be put in a stove or fireplace. Here are some of them.

1. Treated Wood as Firewood

Wood that has been processed and prepared to be sold can be treated by the producers. You’ll often find this described as pressure-treated wood. It’s the wood that is sold for outdoor use. The wood is treated with a copper-based chemical that is applied under heavy pressure. The copper fills the pores of the wood and repels moisture and mildew. However, it’s toxic when it is burned.

Excess lumber is a great source of free firewood; you can find it at construction sites or whenever someone is doing home renovations. However, you need to make sure it’s not treated. You can determine if it’s treated by checking the color. Since it’s treated with a copper chemical, it often turns a shade of green. Newer treated wood is treated with borate, but many manufacturers add a green tint to the wood so that it can be identified as treated. Not all treated wood is colored as such, though. The final method for determining is to smell the wood. Treated wood often smells oily, instead of the fresh scent of raw lumber.

Lastly, if you have any doubt, don’t burn the lumber. You can use it to build a fence or patch a hole in your roof, but don’t burn it.

2. Painted Wood as Firewood

Painted wood, like treated wood, should never be burned because the chemicals on the wood can be toxic. There are some paints that actually aren’t as dangerous as others when burned. However, they are often still made of hydrocarbons which is basically like burning gasoline indoors. Also, burning paint produces a noxious smell that you don’t want in your house.

If you are given painted wood, you have a couple of options. If the paint is water-based and fairly old, you can likely blast it away with a sandblaster or a pressure washer. If you can remove every trace of paint, you can burn the wood as long as it’s not treated lumber. However, this will likely use more resources than you would save. Therefore, the best option is to use the painted lumber for building materials and find something more suitable to burn.

3. Firewood From Far Away

Every year, pests and diseases affect trees all over the world. Some of them, such as citrus greening, are incredibly damaging to crops and incredibly expensive. In the United States, entire states are actually quarantined because citrus greening has been found in those areas. Also, many states or areas are quarantined because of borer pests and other diseases. All of these diseases spread most efficiently when they are carried from place to place by humans. That’s why you shouldn’t buy a cord of wood from an unknown source even if it’s a good deal.

For example, if you live in an area with ash borers that feed on ash trees and you take firewood into a new area, you could be introducing the ash borer to that new area. If you’ve moved farther than the ash borer can readily travel, you’ve likely spread it to an entirely new habitat. For that reason, you should not source firewood from far away from your home unless you know specifically what kind of firewood it is. You need to know where it comes from as well. For example, if it’s oak firewood from an area that is known for citrus greening, it’s likely fine. The most important aspect is knowing where the wood comes from if it comes from far away.

Do you know how to measure firewood? Read my article: How much is a cord of wood?

4. Moldy Firewood

When wood is left outside and not stacked properly, it can develop mold and mildew. That can happen to fallen branches lying on a muddy ground or a stack of firewood not properly covered. If that happens, you need to remove the mold before you use the wood. Mold can be dangerous to anyone who has allergies, a compromised immune system, or respiratory sensitivities. Also, mold travels very easily. Mold spores can be microscopic; they travel on the wind and on your clothes whenever you move the wood.

 

To kill the mold, you need to dry it completely. A wood moisture meter is a great investment for this; that will help you identify wood that is too moist and prevent mold in the first place. If you need to dry the wood and kill the mold, spread it out on a tarp. Make sure no two pieces of wood are touching. Spread them out in the sun and leave them there until they’re completely dry. Then, you need to knock off all of the mold. Wash your hands and leave your clothes outside after you’ve handled mold; that will help prevent it spreading inside. Moldy or rotten wood can also spread its rot when you burn it. Not all diseases and spores are instantly killed by the fire. If your fire wood is mouldy is it likely to be ‘wet’ and will not burn well anyway.

A good way to keep your firewood dry and mould free is to store it in off the ground on a covered waterproof log rack.

It is also a good practice to check the moisture content of your firewood. Wet firewood does not burn as efficiently as dry firewood as the fire’s heat is cooled whilst drying wet wood. Properly seasoned firewood should have a moisture content of less than 20%. You can measure the moisture content of firewood with a specially designed firewood moisture meter.

 

5. Plywood, Chipboard (Particleboard) or Medium Density Fiberboard (MDF) as Firewood

Unless specifically stated to be hardwood, these are typically made from pine. The sheets (plies), chips or fibers are glued together. Softwood is already not an ideal fuel source; it smokes and burns quickly. It also leaves creosote on your chimney or stove.

Then, when you consider the glue, the plywood, chipboard and MDF are far from ideal firewood sources. Many types of glue are nontoxic but become toxic when they’re burned. Some are nontoxic when they burn but smell bad and leave soot all over your stove and your home.

6. Driftwood as Firewood

If you live near the water, you might find driftwood on the shore. It takes a very long time to dry driftwood enough to burn. Even then, you shouldn’t burn it. Driftwood is filled with saltwater and other minerals.  Salt-saturated driftwood can release toxic chemicals when burned, according to the EPA and this can be harmful to your health. This is obviously a very dangerous situation.

 

If you find driftwood, you’re much better off using it to build furniture. It’s rare enough that you probably don’t want to burn it anyway.

Related: Read my article about how to Get FREE lumber for woodworking and DIY

7. Yew, Oleander and ‘Poison’ Plants as Firewood

There are some species of tree that you simply shouldn’t burn because they are irritants or even poisonous. You shouldn’t burn anything with the word “poison” in the name. Trees such as poison walnut are not named that for some esoteric reason; it’s called poison because it is poisonous. Touching the tree, interacting with the leaves, and inhaling the smoke can cause allergic reactions. Yew is typically safe to touch and handle; it’s the wood commonly used for wooden longbows. However, the smoke from burning yew can be an irritant. It will affect everyone differently. If you’re immunocompromised or particularly vulnerable to yew, it can cause serious irritation.

Every part of oleander is an irritant. Burning it can result in pulmonary poisoning. Don’t burn these trees inside or outside. Make sure you can identify them and avoid them.

There are some great sources of firewood for low or no cost. You just need to put in the legwork to find them. You shouldn’t use any of the above listed woods for firewood; it just isn’t worth the risk.

Don’t forget that even with good wood, it is best burnt when it is dry (has a low moisture content). Burning wet wood consumes a lot of the heat evaporating the moisture in the wet wood. You can determine the moisture content of your fire wood using a firewood moisture meter. If your wood has a moisture content over about 20% it is best left to dry until the next winter.