PHOTO: Daniel Johnson
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October 8, 2019

The weather is getting cooler, and as fall continues toward winter, many people will heat their homes via fires in fireplaces or wood stoves. To prepare for this, hobby farmers across the nation are stocking up on firewood. One challenge that comes with a wood-burning stove or fireplace is managing and minimizing creosote buildup in the flue. Creosote is a tar-like substance formed by the combustion of wood. It rises with smoke and can condense inside chimney flues. It hardens and creates a buildup that can be a significant fire hazard.

You can reduce the likelihood of experiencing a creosote chimney fire. These five tips will help minimize and manage creosote buildup:

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1. Ensure Your Wood Is Dry and Seasoned

The most effective way to minimize creosote buildup is to burn dry, seasoned wood. Don’t be tempted to burn freshly-cut “green” wood—the moisture content is too high, leading to a smoky fire with much less heat. In addition to wasting a substantial amount of the wood’s potential heat-generating energy, this combination leads to fast creosote buildup.

How do you know if your wood is dry enough to burn? In general, split firewood that has sat in a well-ventilated area for six months should be adequately dry. Want a more specific measurement? If the wood’s moisture content is less than 20 percent (handheld meters can give you a reading), it’s dry enough to burn.

2. Provide Proper Ventilation

Fires need continuous and ample oxygen to burn effectively. If your fireplace or wood stove doesn’t draw enough oxygen, the wood you burn might not completely combust, increasing the amount of creosote in the smoke. Make sure your wood stove or fireplace meets all specifications and building codes for proper ventilation, and make sure any controls for adjusting air intake are properly set.

3. Keep the Fire Burning Hot

Creosote buildup forms when smoke condensates on the cold walls of the flue. Slow-burning, cool fires won’t generate a high enough temperature in the flue to prevent condensation. A flue temperature above 250 degrees F is considered the range for avoiding condensation. A fire fueled by dry wood and plenty of oxygen helps maintain this temperature (but be careful not go too hot either).

4. Burn Hardwoods, Not Conifers

For several reasons, people are generally advised to burn deciduous hardwoods such as white or red oak, hickory, sugar maple and white ash. These dense woods contain the most potential energy for heating. In contrast, coniferous softwoods (pines, spruces, cedars) are less dense and contain other substances such as resin and pitch that contribute to faster creosote buildup. Some folks suggest using conifers for kindling. These burn fast and hot, helping to quickly heat up the flue. But for the most part, a well-fueled, hot hardwood fire burns cleaner and safer than a coniferous fire.

5. Have Your Chimney Cleaned by a Pro

Ultimately, you cannot eliminate all creosote buildup. You can slow it down and lessen its severity, but for true peace of mind, have your chimney inspected and cleaned regularly by a professional. Doing so annually (or even a couple times a year if you burn wood frequently) can help prevent creosote buildup from reaching the point where the flue liner needs to be replaced.

Enjoy the warmth of your wood fires this winter!

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