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A Message from Your Air District: Clean Wood Burning


A Message from Your Air District: Clean Wood Burning

Winter is almost here. The rains have started, the nights are crisp and cold, and people everywhere are firing up their woodstoves and fireplaces to heat their homes. Many people love this season because of the cozy scarves and sweaters, pumpkin spice lattes, crackling fires, and comfort food; but in the world of air quality we aren’t so romantic; we’re focusing on wood smoke. 

What’s the problem with wood smoke?

It can be a pleasant aroma to remind you of the coming of winter, and it signifies the presence of a toasty, cozy, comfortable fire. But for asthma sufferers and those with odor sensitivities, wood smoke is bothersome and irritating, sometimes debilitating. And the science is out—the particles in wood smoke are good for nobody. That’s why the EPA has spent the last 30 years tightening restrictions on wood burning appliances, and why environmental agencies like the Northern Sonoma County Air Pollution Control District are incentivizing retirement of old, dirty wood-burning appliances. 

In urban and suburban areas, such as the greater Bay Area including Santa Rosa, there are efforts underway to limit wood burning, such as the “Spare the Air” and “Don’t Light Tonight” notices you might hear or see advertised on certain days during the winter season. Programs such as this have been shown to benefit wintertime air quality, because they reduce one of the largest wintertime sources of harmful atmospheric pollutants, making the air better for everyone. In the city, where natural gas can be easily plumbed to any household to use as a heat source, reducing wood burning is feasible. Meanwhile, in the north and western (i.e. more rural) parts of Sonoma County, which is under jurisdiction of a separate (rural) air district, gas service is not as common, and much of the population depends on wood burning appliances to heat their homes. In these areas, restricting wood burning is not very practical. Moreover, in heavily wooded areas, wood (and therefore heat) can be free or next-to-free, providing an economic incentive to use wood over gas. Air quality policy makers in rural areas recognize the demand, and sometimes the necessity, for wood burning. Also, because the background air quality is generally cleaner in rural areas, including the northern and western parts of Sonoma County, rural air districts don’t have a need to make such strict wood burning rules—yet.* (More to come on this later.)

If you happen to be a resident who depends on a wood burning appliance to heat your home, or if you simply love building your fires and don’t want to give them up, keep in mind there are ways to optimize your wood burning to get better heat, reduce wood smoke, and be a better neighbor to those that share the air around you. The first and most effective way to improve your wood burning smoke output is to use an EPA-certified wood burning appliance.

What’s the big deal about EPA-certified appliances?

 Mainly, they are tested and certified to emit less than 4.5 grams of fine particulates per hour of burning. This is in contrast to older, non-certified wood stoves, which emit over 30 grams per hour, or built in fireplaces, which can emit up to 90 grams per hour. There are a couple of different technologies that make EPA-Certified stoves work so well, but they all operate on the principal that in order to burn wood clean, you need “complete combustion.” The more complete the combustion, the less sooty smoke you have rising out of the chimney. The problem with old woodstoves or fireplaces is that they are too simple inside; with just a firebox and a flue, the wood and exhaust don’t get hot enough to completely combust all the wood particles; these particles rise out of the chimney as smoke.

One of the simplest components of an EPA-certified stove is firebox insulation. In order to ensure that the fire gets hot enough for complete combustion, the firebox is insulated all the way around. Additionally, the incoming air takes a circuitous path into the firebox, and along that path it gets heated up by the existing fire--and the hotter the air that fuels a fire, the hotter the fire’s temperature will be.

There are two main types of EPA-certified wood burning appliances: catalytic and non-catalytic.

A catalytic stove contains a honeycomb-like catalytic combustor within its flue that, through a chemical reaction, causes wood smoke to burn up at a lower temperature, meaning the entire stove doesn’t need to be as hot as it would otherwise need to be in order to attain complete combustion. Wood stoves like this are very effective, and have emissions that sometimes rival pellet stoves in their cleanliness and efficiency. However, the catalytic combustor needs to be cleaned at regular intervals, and occasionally replaced, for this technology to work properly. Non-catalytic stoves do not use such a device; they depend on higher temperatures, and recirculation of the exhaust within the firebox, to achieve complete combustion. These types of stoves have baffles within them that causes the exiting exhaust to take a long, circuitous route, being heated and re-burned along the way, before it goes up the chimney. Non-catalytic woodstoves need maintenance as well, to ensure the airflow is working properly and the insulation and baffling are intact and functional.

All types of EPA-certified woodstoves are great at providing wood heat while emitting a fraction of the pollution—if they are used properly. Unfortunately, whether or not they have an EPA-certified woodstove, there are certain things some people do that can sabotage the technology and cause more smoke to rise out of the chimney. This isn’t just more smoke, it’s more lost fuel not being turned into heat. The more smoke you emit, the less efficient of a heat source you’re getting from your wood fuel. It is important to remember certain concepts when using your wood burning appliances: 

Burn dry, seasoned wood. That tree you just felled and split a couple months ago? It’s not ready yet. Softwood takes at least 6 months and hardwood at least one year to properly cure. If your wood is not dry enough, the moisture within will cause the fire to burn at a lower temperature, compromising your stove’s ability to arrive at the conditions necessary for complete combustion. This also goes for wood that may have been seasoned, but has been left out in the rain. Wood needs to be kept dry after it has seasoned by being stored off the ground in a structure that keeps it covered. Burning wet or unseasoned wood is the number one mistake residents make that has a profound effect on their neighborhood air quality. You might as well be misting your fire with a spray bottle. 

Never burn garbage. It’s prohibited by law and if you get caught, you can be fined. Please, don’t burn anything other than wood in your appliance. Burning garbage, such as paper (other than black & white newspaper used for kindling), plastic, Styrofoam, treated wood, and other substances, releases harmful toxic gases into your air. Please don’t do this to yourself and your neighbors.

Allow proper air flow into, and out of, your stove. Some folks might believe that limiting the air flow to a woodstove might help their fire last longer, saving them money on wood fuel. On the contrary, without enough air, wood smolders and smokes, belching large amounts of unburned wood fuel (and dollars) out of your chimney. Give the fire enough air to breathe and heat up sufficiently, and you’re not only helping with complete combustion; you’re maximizing the amount of heat you get out of your wood fuel. Similarly, don’t narrow the flue in an effort to make your stove hotter. This just interrupts the path of the exhaust, which interferes with the process of complete combustion and can damage the components of your firebox. Airflow into and out of your stove should be in accordance with your owner’s manual to ensure the cleanest and most efficient burn. 

Clean and maintain your appliance and chimney. Make sure you remove the ash within the firebox regularly—too much ash can interfere with the airflow. Also, clean your chimney on a regular basis. Again, too much buildup within the chimney restricts airflow (and can be a fire hazard). Check your owner’s manual for other maintenance that needs to happen on your particular model of appliance.

Use only manufacturer components in your appliance. Every once in a while you may need to purchase parts to maintain or repair your wood heating appliance. Be sure those parts are in accordance with the original manufacturer specs. The problem with aftermarket parts, especially those that have to do with airflow, is that they might not be structured the same, interfering with preheating of the inlet air, or exhaust gas recirculation. This could prevent complete combustion, and compromises the integrity of your stove. Stick with manufacturer parts and you’ll be sure your stove continues to function as it was built to do.

*So, are you wondering if there are any stricter wood burning regulations pending in the rural northern and western Sonoma County? No, there aren’t. But that isn’t a guarantee that there won’t be in the future. The rural areas of the Northern Sonoma County Air Pollution Control District, especially the river valleys, are full of pockets where the air sits stagnant, particularly on cold days. In these areas and in general, it only takes one person burning badly to turn the air quality nasty in an entire neighborhood. We all need to work together to be good neighbors and good stewards of our environment to ensure that wood burning can remain sustainable as our population grows. Think about your family and your neighbors when you’re lighting your toasty, cozy fire, and be sure to burn smart and burn clean. 

By Jessica DePrimo, Air Quality Specialist III and Grant Program Manager, NSCAPCD

More information can be found on the following websites, sourced in the writing of this article:

For information on Northern Sonoma County Air Pollution Control District Woodstove Change-Out incentives, visit