Health and Emissions

The amount of particulate matter released by your wood burning appliance is an important consideration when purchasing a new or used stove. In 1990, the EPA came out with regulations governing wood stove emissions that all wood stove manufacturers had to comply with. The initial emissions limit was 4.5 grams of smoke per hour or g/h. These regulations have since been replaced in May of 2020 when the standard was lowered to 2.0 g/h.

Manufacturers of wood stoves have greatly improved on the efficiency of their wood stoves over time with some stoves today reaching a 1-1.5 g/h limit. When looking for a new stove, consider finding a model with the EPA white label as a lower g/h translates into a cleaner, more efficient stove.

Wood combustion produces fine particulate matter. Also known as PM 2.5, it is a material smaller than 2.5 micrometers in size. It can penetrate the deep lungs in a human body and can cause coughing, sneezing, runny nose, heavy breathing, and irritation in the eyes, nose, throat, and lungs. Long term exposure can cause asthma, bronchitis, reduced lung function, and increased cancer risk. Long term exposure to children can have adverse effects on physical development.

When wood is burned, it also creates uncombusted particles, with the most dangerous being polycyclic aromatic hydrocarbons (PAH). This is a dangerous mix of particles known to cause high rates of birth defects, lower birth weights, difficulty reproducing and weakened immune systems.
Carbon Monoxide or CO is also created during combustion. It is a toxic gas that can cause exhaustion, chest pains and nausea in low concentrations. In high concentrations however, carbon monoxide can be deadly.

Wood Stoves:
Wood stoves are space heaters and work best in homes that contain open floor plans, allowing for heat to circulate easily. Catalytic stoves or stoves that contain a ceramic honeycomb to lower the temperature at which stove gases will burn, provide the user with a steeper learning curve than your typical non-catalytic stove which is what most stoves on the market are. The importance of a catalytic stove is in the efficiency as the smoke passes through the catalytic honeycomb, the harmful particulates are burnt away allowing for increased efficiency and less emissions. Non-catalytic stoves do not contain a honeycomb and utilize firebox insulation and baffles to recirculate combustion air to achieve more complete combustion. This method can increase efficiency and produce a cleaner burn.

Current list of EPA Approved Wood Stoves: https://cfpub.epa.gov/oarweb/woodstove/index.cfm?fuseaction=app.about

Outdoor Wood Boiler and Pellet/Wood Boilers:
There are two kinds of wood fired boilers, standard hydronic and two-stage gasification cord wood or pellet boilers. These systems can differ drastically with emissions, efficiency, and cost. Most boilers range in heat output from 50,000 to 200,000 BTUs/hr. Boilers that burn cord wood range from $9000-$16,000. Boilers that burn pellets can range from $14,000-$23,500. Any type of boiler like this can be used to heat water of glycol (antifreeze) or used with duct work as a forced air system.

Outdoor Wood Boilers suffer from design problems that make them well known for producing high emissions and lower efficiency. These systems contain a large firebox which tends to produce larger fires that smolder, they heat a water jacket which in most systems remains improperly insulated, and they have low exhaust stacks which allow the exhaust to hover close to the ground and not away from the system. These systems can release four to 12 times more emissions than wood stoves and 10 to 20 times more emissions than EPA-certified wood stoves. A few more things to note about OWB’s is that they can produce excess smoke from on-off cycling, oxygen deprived burning conditions, and low smokestacks as previously mentioned. Large fireboxes and the location of these systems being outside, they are more prone to abuse with operators of OWB’s burning wet wood, leaves, garbage and other extremely harmful materials. While the EPA has initiated a voluntary regulatory program to encourage manufacturers to produce cleaner, more efficient units there are still many unqualified, unhealthy boilers on the market. So be cautious when purchasing and installing one of these systems.

In early 2011, the New York State Department of Environmental Conservation (DEC) instituted regulations governing OWBs. These limit the types of OWBs that can be sold in the state and were designed to offer guidelines for the optimal use of these units (to minimize emissions, mainly). Provisions for phasing out existing units did not make it into the final legislation.

The two-stage gasification systems are much more efficient and cleaner-burning than single stage systems (previously mentioned OWB’s). With two-stage combustion, the combustible material (cord wood or wood pellets, typically) is heated in one chamber in the relative absence of oxygen, and the gases are released into another chamber where fresh air is injected, which puts the combustion into overdrive and burns the gases almost completely, at much higher temperatures than can be reached in a wood stove, pellet stove, or traditional outdoor wood boiler. 

Last updated January 23, 2024