Outdoor Wood Boilers

Wood Boiler Basics

An outdoor wood boiler is any furnace, stove or boiler designed to burn wood, where the unit is not located within a building intended for habitation by humans or domestic animals. They are also known as water stoves and wood-fired hydronic heaters, and typically look like small utility buildings with a smoke stack. Outdoor wood boilers provide heating and/or hot water to a single residence.

Fire Wood Quality

The quality of the fire wood can have a large effect on the amount of smoke that is produced and on the efficiency of the boiler.

  • Only burn dry, untreated wood. Do not burn wet wood, treated wood or trash. Burning solid waste materials such as treated wood, plastic, rubber and asphalt is prohibited statewide. Burning treated wood and plastics releases toxic chemicals such as heavy metals and dioxins that can cause a range of health issues including skin, reproductive and developmental problems and increase the risk of cancer.

  • Do not use lighter fluid, gasoline or other chemicals to start the fire. Their fumes contribute to the formation of ground-level ozone, an air pollutant that is particularly harmful for people with respiratory and heart diseases. Instead, use clean, dry kindling to start the fire.

  • Follow manufacturer’s written instructions for wood loading. This will help the furnace burn efficiently, reducing both wood usage and air emissions. Remember, even dry, untreated wood releases some pollutants when it burns.

Firewood Size

Size of the firewood can also play an important factor in smoke emissions and efficiency. A full load of small wood will present a large amount of surface area to the fire. This effect is similar to burning kiln-dried wood. The fire will burn fast, spend too short a time in the boiler to transfer heat well and create a lot of smoke. Mix small diameter pieces of firewood with larger pieces of firewood.

Do NOT Burn garbage & other inappropriate materials

Particleboard, treated, stained, painted or wet wood and trash should never be burned in OWBs. The burning of most solid waste materials, including treated wood, plastics, rubber and asphalt, is prohibited in Wisconsin. The combustion of treated wood, agricultural plastics and other garbage releases heavy metals and toxic chemicals such as polycyclic aromatic hydrocarbons and dioxins. Exposure to dioxins is linked to skin problems, reproductive or developmental problems and increased risk of cancer.