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New Hampshire Department of Environmental Services


Smoke from wood stoves and outdoor wood-fired hydronic heaters contains air pollutants such as fine particulates, nitrogen oxides, sulfur oxides, carbon monoxide, volatile organic compounds, dioxins and furans. The fine particulates of wood smoke ten microns or less in diameter (a human hair is approximately 70 microns in diameter), can be inhaled deep into the lungs, collect in tiny air sacs where oxygen enters the blood (called alveoli), and cause breathing difficulties and sometimes permanent lung damage.

Wood smoke is a particular concern in the winter, when cold stagnant air and temperature inversions limit air movement. Communities located in valleys are more strongly affected. As wood burning increases on cold, clear, calm nights, smoke is unable to rise and disperse. Pollutants are trapped and concentrated near the ground, and the small size of the particles allows them to seep into houses through closed doors and windows.

Burning Efficiently

You can reduce the amount of smoke from wood stoves and outdoor wood-fired hydronic heaters (outdoor wood boiler) by choosing low-emission certified units, operating them properly, and using good quality firewood. This improves combustion efficiency, reduces emissions, helps protect public health and the environment, and saves fuel costs.

Follow these tips:

  • Burn the right wood. Use only dry seasoned cordwood.
  • Use the right stove. It's best to use an EPA certified wood stove or a Phase II Outdoor Wood Boiler, they burn less wood.
  • Burn the right way. Be sure to clean your stove and pipes each year. Maintain a bright, hot fire in the wood stove and do not let it smolder.

Indoor Wood Stoves

New Hampshire does not currently regulate indoor wood stoves, but does encourage the use of EPA certified wood stoves. For more information on indoor wood stoves please visit EPA's Burn Wise website at

Outdoor Wood Boilers

Effective August 10, 2008, New Hampshire established RSA 125-R Outdoor Wood-Fired Hydronic Heaters. This statute establishes certain requirements on the sale, installation, and use of these devices.

There are three categories of outdoor wood boilers: Phase I, Phase II and Non-phase I or II units. Phase II units are the cleaner burning units with an emission limit of 0.32 pounds of particulate matter or less per million BTUs of heat output.

Effective April 1, 2010, New Hampshire prohibits the sale of any outdoor wood boiler other than a Phase II unit.

Effective August 10, 2008, outdoor wood boiler installations must meet the following criteria:

  • Phase I units:
    • Must be installed at least 100 feet from nearest property line.
    • Must have a stack height at least 2 feet higher than the peak of the roof of a residence or business not serviced by the unit located within 300 feet of the unit.
  • Phase II units:
    • Must be installed at least 50 feet from nearest property line.
  • Non Phase I or Phase II units:
    • Must be installed at least 200 feet from nearest abutting residence.
    • Must have a stack height 2 feet higher than peak of the roof of residence or business not served by the unit located within 300 feet of the unit.

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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