OLR Research Report

May 19, 2008





By: Paul Frisman, Principal Analyst

You asked (1) for a summary of Connecticut's laws on outdoor wood burning boilers (OWBs), (2) how neighboring states are regulating OWBs, and (3) whether Connecticut law addresses newer, less polluting OWBs.


Connecticut regulates OWB siting, the height of OWB smokestacks, and the opacity (density) of the smoke they produce. Maine and Vermont limit OWB emissions and their location, and Massachusetts has proposed setting emission limits.

The U.S. Environmental Protection Agency (EPA) does not regulate OWB emissions, but has agreed with a number of OWB manufacturers on a voluntary program to produce cleaner OWBs. These models, which carry an orange tag, are 70% less polluting than other models. Connecticut law does not address these newer models.

A nonprofit association of northeastern air quality agencies, the Northeast States for Coordinated Air Use Management, or NESCAUM, proposed model OWB regulations in 2007. Several states are basing proposed regulations on the NESCAUM model, whose proposed emission

limits are stricter than those in the EPA agreement. Information on NESCAUM's model regulations and its study of OWBs can be found online at:


An OWB, also known as an outdoor wood-burning furnace or hydronic heater, is essentially a wood-fired boiler in a small, insulated shed with a smoke stack. It heats water that is carried through underground pipes to heat a home or building, a swimming pool, Jacuzzi, hot tub, or domestic hot water. The popularity of OWBs has increased as the cost of oil and gas has risen.

A number of studies have found that OWB emissions pose a health threat. According to “Smoke Gets in Your Lungs,” an October 2005 report from the New York attorney general's office, OWBs “may be among the dirtiest and least economical modes of heating, especially when improperly used.”

Wood smoke contains a complex mixture of gases and soot particles. The gases include carbon monoxide, nitrogen and sulfur oxides, volatile organic compounds, and others associated with deleterious health effects. The soot particles (also called particulate matter or PM) are small enough to enter a person's lungs, and can lead to serious respiratory problems.

Even when used properly, the report stated, OWBs emit about four times as much fine particulate matter as conventional wood stoves, 12 times as much as EPA-certified wood stoves, 1000 times more than oil furnaces, and 1,800 times more than gas furnaces. The health effects of OWBs emissions are made worse, studies state, because, (1) unlike wood stoves, they are often operated year-round; (2) their design “encourages burning of inappropriate materials,” such as refuse, tires, wood waste, and railroad ties; and (3) their relatively short smokestack height allows smoke to travel to neighboring buildings.

Approaches to Regulating OWBs

EPA does not regulate OWBs, and states have taken several approaches in regulating them. A number of states, including Connecticut, have implemented setback and stack height requirements for OWBs. Connecticut law (CGS 22a-174k) also requires that OWB operators burn only wood that has not been chemically treated.

Connecticut law applies only to OWBs installed after July 8, 2005. OWBs installed or operated before that date are not subject to these restrictions.

States also can regulate the use of OWBs and other smoke-generating sources through smoke opacity (density) regulations, although the transient nature of smoke emissions may make these hard to enforce. Zero percent opacity means no smoke is visible; 100% opacity would be smoke too thick to see through. Connecticut's opacity limit is an average of 20% during six consecutive minutes, or a 40% average for one minute (Conn. Agency Regs. 22a-174-18 (b) (1)).

Some states, such as Maine and Vermont, restrict OWB emissions. Massachusetts and Ohio are considering doing so.

Connecticut Law

CGS 22a-174k, enacted in 2005, bans the installation or operation of OWBs that do not meet certain requirements. A violation of the law is an infraction.

With a few exceptions, the law prohibits anyone from building, installing, establishing, modifying, operating, or using an OWB until EPA regulations governing them take effect.

The law allows OWBs if they were either built, modified or in use before July 8, 2005; or they

1. are installed at least 200 feet from the nearest neighboring home;

2. have a chimney shorter than 55 feet tall but at least as tall as the roof peaks of neighboring homes within 500 feet of the OWB;

3. burn only wood that has not been chemically treated; and

4. are installed and operated according to the manufacturer's written instructions, provided the instructions comply with the law.

Under the law, an OWB is an accessory structure or appliance designed to (1) be located outside living spaces ordinarily used for human habitation and (2) transfer or provide heat, through liquid or other means, through the burning of wood or solid waste. Under the law, these furnaces heat (a) spaces other than where they are located; (b) any other structure or appliance on the premises; (c) domestic water; or (d) water used in a swimming pool, hot tub, or Jacuzzi. The law does not apply to fire pits, wood-fired barbecues, or “chimineas” (decorative fireplaces).

Anyone who operates an OWB in violation of the law commits an infraction, punishable by a fine of up to $90. Each day the furnace operates is considered a separate violation. The Department of Environmental Protection (DEP) commissioner or a town or city affected by a furnace's operation or potential operation can enforce the law.

In 2008, a bill that would have allowed an OWB buyer to cancel his or her purchase agreement in certain circumstances (HB 5804) was favorably reported by the Environment Committee, but died in the Judiciary Committee.


NESCAUM issued model regulations on January 29, 2007. They can be found at NESCAUM's website (http: //www. nescaum. org/topics/outdoor-hydronic-heaters). Among other things, the regulations propose emissions limits for residential OWBs of 0. 44 pounds per million British Thermal Units (lb. /mmBTU) starting April 1, 2008, and 0. 32 lbs. /mmBTU starting April 1, 2010. (A British thermal unit is a unit of energy. One BTU is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit.)

The model regulations also propose setback limits that vary according to the OWB's emissions rate, prohibits people from operating them between April 15 and September 30 unless they meet the emission limits, and limits the types of fuel that can be burned.


State Emissions Requirements

Vermont. As of March 31, 2008, all OWBs sold or distributed in Vermont must meet PM limits of 0. 44 lb. /mmBTU. Also by that date, the Agency of Natural Resources secretary must file a proposed rule to establish a PM limit of 0. 32 lb. /mmBTU (10 VSA 558). Vermont requires all OWBs to be located more than 200 feet from any home other than the one it serves. The OWB must have a stack that extends higher than the roof peak of the structure it serves if any other home is located within 500 feet of it.

Maine. As of April 1, 2008, no one can sell or distribute an OWB unless it meets a PM limit of 0. 60 lb. /mmBTU. Starting April 1, 2010, no one can sell or distribute an OWB unless it meets a PM limit of 0. 32 lb. /mmBTU (Code of Maine Rules, 06-96, Ch. 150). Unlike the siting requirements in Connecticut and Vermont, Maine's setback requirements depend on OWB emissions. OWBs with PM emissions that exceed 0. 60 lb. /mmBTU must be at least 250 feet from the nearest property line. OWB's that meet emission limits of 0. 60 lb. /MmBTU must be installed at least 100 feet from the nearest property line. OWBs with emission limits of 0. 32 lb. /mmBTU must be installed at least 50 feet from the nearest property line. Regardless of its PM emission rates, no OWB may be installed closer than 500 feet from the property line of a state licensed school, daycare, or health facility. Stack height requirements also vary by emission limits.

Massachusetts. Massachusetts is proposing emissions standards identical to those in NESCAUM's model rule: 0.44 lb/mmBTU for residential OWBs sold after October 1, 2008 (phase I) and 0.32 lb/mmBTU for residential OWBs sold after March 31, 2010 (phase II). In addition, Phase II limits total particulate matter emitted to 15 grams per hour.

The Massachusetts DEP will hold hearings on the proposed regulations in June 2008. Information on the proposed Massachusetts standards is available online at:


In 2007, the EPA agreed with a number of OWB manufacturers on a voluntary program to produce cleaner OWBs. The cleaner models must emit no more than 0.60 lb/mmBTU. Nineteen manufacturers are taking part in the voluntary EPA program. EPA maintains a list of OWBs that meet its standards at http://epa.govowhh/models.htm.