The greenest way to make a holiday fire.

Illuminating answers to environmental questions.
Dec. 22 2009 9:31 AM

Hearth Burn

The greenest way to make a holiday fire.

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So far we've talked about what goes into a log; now let's consider what comes out of it. You might think that burning natural firewood would produce the cleanest emissions. In fact, the opposite is true. When organic material doesn't burn all the way through, it releases tiny bits of particulate matter—linked to lung and heart disease, not to mention burning eyes and runny noses—and other hazardous substances, such as carbon monoxide, benzene, formaldehyde, and polycyclic aromatic hydrocarbons. Concerns about emissions from fireplaces are great enough that some communities call for "burn bans" on days when the air quality is particularly low.

Artificial logs emit all the same pollutants as natural firewood, but they do so at significantly lower rates. A 2005 report from the EPA and Environment Canada (PDF) analyzed emissions from several varieties of fake logs, including those made from sawdust and coffee grounds, and compared them with reported figures for firewood. On average, a fire built with fake logs emitted 9 grams of particulate matter per hour, while wood-fueled fires emitted 36 grams. The fakes also released less carbon monoxide: 42 grams per hour, compared with firewood's 214 grams. The fakes also produced much less carbon monoxide, benzene, formaldehyde, and polycyclic aromatic hydrocarbons.

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There were some differences observed among the fakes, though. The coffee logs, for example, produced slightly less particulate matter than the others and had the second-lowest carbon monoxide, formaldehyde, and polycyclic aromatic hydrocarbon emissions. However, the differences between the best- and worst-performing fakes were much smaller than the differences between the most-polluting fakes and firewood.

Franken-logs tend to outperform their natural cousins because they pack in much more energy per unit of weight, on account of their wax content and relative lack of moisture. That means you don't have to burn nearly as much fake wood to get an equivalent amount of heat and light. The fake logs also burn more completely, producing fewer pollutants.

If you already have wood piling up in your backyard, however, the Lantern thinks you should use what you've got rather than buy a fake log that's less polluting. Just make sure that tree came down early in the year. Wood that's properly dried, or "seasoned," burns more cleanly and efficiently. (Getting your fire as hot as possible, as quickly as possible, will also reduce emissions.) The EPA's Burn Wise campaign recommends splitting wood into logs  3 to 5 inches in diameter and then storing them outdoors, covered and off the ground, for at least six months before burning. If you have a lot of wood and use your fireplace often, you might consider investing in a moisture meter. Otherwise, knock two logs against one another—if they're dry enough, they'll make a hollow sound, as opposed to a dull thud.

Is there an environmental quandary that's been keeping you up at night? Send it to ask.the.lantern@gmail.com, and check this space every Tuesday.

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Nina Shen Rastogi is a writer and editor, and is also the vice president for content at Figment.