06-96 DEPARTMENT OF ENVIRONMENTAL PROTECTION

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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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Chapter 150: CONTROL OF EMISSIONS FROM OUTDOOR WOOD BOILERS

SUMMARY: This regulation establishes particulate emission 

standards, siting criteria and labeling requirements for outdoor wood 

boilers, including outdoor pellet boilers.

1. Applicability

A. This regulation applies statewide.

B. This regulation applies to any manufacturer, supplier, distributor or person intending to 

sell, lease, distribute, or market, an outdoor wood boiler, including an outdoor pellet 

boiler, in the State of Maine that meets the definition of an outdoor wood boiler and to 

any person who installs, operates or owns an outdoor wood boiler, including an outdoor 

pellet boiler.

C. This regulation applies to outdoor wood boilers, including outdoor pellet boilers, with a 

rated thermal input of less than 3 MMBtu/hr. Boilers with a rated thermal heat input of 3 

MMBtu/hr or greater are subject to Chapter 103 Fuel Burning Equipment Particulate 

Emission Standard of the Department’s Regulations.

2. Definitions

The following terms, as used in this Chapter, have the following meanings:

A. Clean wood. “Clean wood” means wood that has no paint, stain, or other types of 

coatings, and wood that has not been treated with, including but not limited to, copper 

chromium arsenate, creosote, or pentachlorophenol.

B. Commercial outdoor wood boiler. “Commercial outdoor wood boiler” means any 

outdoor wood boiler, except for those outdoor wood boilers used solely for space heating 

or domestic hot water, used to service a commercial establishment.

C. Distribute or sell. “Distribute or sell” means to distribute, sell, advertise for sale, offer 

for sale, lease, ship, deliver for shipment, release for shipment, or receive and (having so 

received) deliver or offer to deliver. This term does not include the distribution or sale by 

a manufacturer of an outdoor wood boiler that is installed outside the State of Maine.

D. Manufacturer. “Manufacturer” means any person who constructs or imports for the 

distribution or sale into the United States an outdoor wood boiler.

E. New outdoor wood boiler. “New outdoor wood boiler” means an outdoor wood boiler 

that is not installed and/or operational at the intended location of use as of the effective 

date of this Chapter.

F. Nuisance. “Nuisance” means emission of air contaminants to the outdoor atmosphere of 

such quantity, characteristic or duration that may be injurious to human, plant or animal 

life or to property, or that unreasonably interferes with the comfortable enjoyment of life 

or property.
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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G. Opacity. “Opacity” means the degree to which emissions other than water reduce the 

transmission of light and obscure the view of an object in the background.

H. Outdoor wood boiler. “Outdoor wood boiler” (also known as outdoor wood-fired 

hydronic heater, water stove or outdoor wood furnace) means a fuel burning device that:

(1) is designed to burn wood, biomass fuel products or other approved solid fuels; (2) the 

manufacturer specifies for outdoor installation or installation in structures not normally 

occupied by humans (e.g., sheds) or is an indoor-rated device housed in a modular or 

containerized structure; and (3) heats building space or water, or both, through the 

distribution, typically through pipes for a fluid or ducts for air, of a fluid or air heated in 

the device.

I. Outdoor pellet boiler. “Outdoor pellet boiler” means an outdoor wood boiler designed 

and warranted by the manufacturer specifically to burn pellet fuel with metered fuel and 

air feed and controlled combustion engineering, which is operated according to the 

manufacturer’s specifications and burns only pellet fuel.

J. Particulate matter or PM. “Particulate matter or PM” means particulate matter PM10

and PM2.5 including the condensable fraction.

K. Sale. “Sale” means the transfer of ownership or control.

3. Requirements for the Sale, Installation and Operation of New Outdoor Wood Boilers

and Outdoor Pellet Boilers

A. Particulate Matter Emission Standards for Outdoor Wood Boilers

(1) Phase I Particulate Emission Standard for Outdoor Wood Boilers and Outdoor Pellet 

Boilers. No person shall distribute or sell, lease, import, supply or install an outdoor 

wood boiler after April 1, 2008 or an outdoor pellet boiler after April 1, 2009 unless 

it has been certified under Section 3(E) to meet a particulate matter emission limit of 

0.60 lbs/MMBtu heat input. Outdoor wood boilers and outdoor pellet boilers 

meeting the Phase I limit must be installed according to the applicable setback and 

stack height requirements as defined in Section 3(B) and 3(C) of this Chapter.

(2) Phase II Particulate Emission Standard for Outdoor Wood Boilers and Outdoor Pellet 

Boilers. No person shall distribute or sell, lease, import, supply or install an outdoor 

wood boiler or outdoor pellet boiler after April 1, 2010 unless it has been certified 

under Section 3(E) to meet a particulate matter emission limit of 0.32 lbs/MMBtu 

heat output. Outdoor wood boilers and outdoor pellet boilers meeting the Phase II 

limit must be installed according to the applicable setback and stack height 

requirements as defined in Section 3(B) and 3(C) of this Chapter.

(3) Voluntary Technology-forcing Particulate Emission Standard for Outdoor Wood 

Boilers. An outdoor wood boiler meeting a particulate matter emission limit of 0.06 

lbs/MMBtu heat output is not subject to a setback requirement under this Chapter as 

long as it meets the stack height requirements described in Section 3(C)(3) of this 

Chapter.
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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B. Setback Requirements for New Outdoor Wood Boilers and Outdoor Pellet Boilers

(1) Outdoor wood boilers and outdoor pellet boilers with particulate emission limits 

greater than 0.60 lbs/MMBtu heat input or with no certification. No person shall 

install or allow the installation of any outdoor wood boiler or outdoor pellet boiler

that has been certified to meet a particulate emission limit greater than 0.60 

lbs/MMBtu heat input or has no certification, determined in accordance with Section 

3(E) of this Chapter, unless the outdoor wood boiler or outdoor pellet boiler is 

installed at least 250 feet from the nearest property line or at least 270 feet from the 

nearest dwelling that is not on the same property as the outdoor wood boiler or 

outdoor pellet boiler.

(2) Outdoor wood boilers and outdoor pellet boilers certified to meet particulate emission 

limits of 0.60 lbs/MMBtu heat input. No person shall install or allow the installation 

of any outdoor wood boiler or outdoor pellet boiler that has been certified to meet a 

particulate matter emission limit of 0.60 lbs/MMBtu heat input, determined in 

accordance with Section 3(E) of this Chapter, unless the outdoor wood boiler or 

outdoor pellet boiler is installed at least 100 feet from the nearest property line or at 

least 120 feet from the nearest dwelling that is not on the same property as the 

outdoor wood boiler or outdoor pellet boiler.

(3) Outdoor wood boilers and outdoor pellet boilers certified to meet particulate emission 

limits of 0.32 lbs/MMBtu heat output. No person shall install or allow the 

installation of any outdoor wood boiler or outdoor pellet boiler that has been certified 

to meet a particulate matter emission limit of 0.32 lbs/MMBtu heat output, 

determined in accordance with Section 3(E) of this Chapter, unless the outdoor wood 

boiler or outdoor pellet boiler is installed at least 50 feet from the nearest property 

line or at least 70 feet from the nearest dwelling that is not on the same property as 

the outdoor wood boiler or outdoor pellet boiler.

(4) Outdoor pellet boilers certified to meet particulate emission limits of 0.06

lbs/MMBtu heat output. No person shall install or allow the installation of any 

outdoor pellet boiler that has been certified to meet a particulate matter emission limit 

of 0.06 lbs/MMBtu heat output, determined in accordance with Section 3(E) of this 

Chapter, unless the outdoor pellet boiler is installed at least 20 feet from the nearest 

property line or at least 40 feet from the nearest dwelling that is not on the same 

property as the or outdoor pellet boiler.

(5) Outdoor wood boilers that have been modified to burn pellets. Outdoor wood boilers 

that have been modified to burn pellets must meet the applicable setback specified in 

Section 3(B) of this Chapter for the original particulate emission limit certification of 

the outdoor wood boiler, determined in accordance with Section 3(E) of this Chapter.

C. Stack Height Requirements for New Outdoor Wood Boilers and Outdoor Pellet 

Boilers

(1) Outdoor wood boilers and outdoor pellet boilers certified to meet particulate 

emissions limits of greater than 0.60 lbs/MMBtu heat input or with no certification.
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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(a) No person shall install or allow the installation of any outdoor wood boiler or 

outdoor pellet boiler that has been certified to meet a particulate emission limit of 

greater than 0.60 lbs/MMBtu heat input or has no certification, determined in 

accordance with Section 3(E) of this Chapter, unless the outdoor wood boiler or 

outdoor pellet boiler:

(1) has an attached stack with a minimum stack height of 10 feet above ground 

level; or

(2) has an attached stack extending two feet higher than the peak of the roof of 

the structure being served by the outdoor wood boiler or outdoor pellet 

boiler, if an abutting residence is located less than 500 feet from the outdoor 

wood boiler or outdoor pellet boiler.

(b) No person shall operate any outdoor wood boiler or outdoor pellet boiler,

installed after the effective date of this Chapter, that has been certified to meet a 

particulate emission limit of greater than 0.60 lbs/MMBtu heat input or with no 

certification, determined in accordance with Section 3(E) of this Chapter, if an 

abutting residence is located less than 500 feet from the outdoor wood boiler or 

outdoor pellet boiler, unless the outdoor wood boiler or outdoor pellet boiler has 

an attached stack extending two feet higher than the peak of the roof of the 

structure being served by the outdoor wood boiler or outdoor pellet boiler.

(2) Outdoor wood boilers and outdoor pellet boilers certified to meet particulate emission 

limits of 0.60 lbs/MMBtu heat input.

(a) No person shall install or allow the installation of any outdoor wood boiler or 

outdoor pellet boiler that has been certified to meet a particulate matter emission 

limit of 0.60 lbs/MMBtu heat input, determined in accordance with Section 3(E) 

of this Chapter, unless the outdoor wood boiler or outdoor pellet boiler:

(1) has an attached stack with a minimum stack height of 10 feet above ground 

level; or

(2) has an attached stack extending two feet higher than the peak of the roof of 

the structure being served by the outdoor wood boiler or outdoor pellet 

boiler, if an abutting residence is located less than 300 feet from the outdoor 

wood boiler or outdoor pellet boiler.

(b) No person shall operate any outdoor wood boiler or outdoor pellet boiler, 

installed after the effective date of this Chapter, that has been certified to meet a 

particulate emission limit of 0.60 lbs/MMBtu heat input, determined in 

accordance with Section 3(E) of this Chapter, if an abutting residence is located 

less than 300 feet from the outdoor wood boiler or outdoor pellet boiler, unless 

the outdoor wood boiler or outdoor pellet boiler has an attached stack extending 

two feet higher than the peak of the roof of the structure being served by the 

outdoor wood boiler or outdoor pellet boiler.

(3) Outdoor wood boilers and outdoor pellet boilers certified to meet particulate emission 

limits of 0.32 lbs/MMBtu heat output.
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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(a) No person shall install or allow the installation of any outdoor wood boiler or 

outdoor pellet boiler that has been certified to meet a particulate matter emission 

limit of 0.32 lbs/MMBtu heat output, determined in accordance with Section 3(E) 

of this Chapter, unless the outdoor wood boiler or outdoor pellet boiler:

(1) has an attached stack with a minimum stack height of 10 feet above ground 

level; or

(2) has an attached stack extending two feet higher than the peak of the roof of 

the structure being served by the outdoor wood boiler or outdoor pellet 

boiler, if an abutting residence is located less than 300 feet from the outdoor 

wood boiler or outdoor pellet boiler.

(b) No person shall operate any outdoor wood boiler or outdoor pellet boiler, 

installed after the effective date of this Chapter, that has been certified to meet a 

particulate emission limit of 0.32 lbs/MMBtu heat output, determined in 

accordance with Section 3(E) of this Chapter, if an abutting residence is located 

less than 300 feet from the outdoor wood boiler or outdoor pellet boiler, unless 

the outdoor wood boiler or outdoor pellet boiler has an attached stack extending 

two feet higher than the peak of the roof of the structure being served by the 

outdoor wood boiler or outdoor pellet boiler.

(4) Outdoor pellet boilers certified to meet particulate emission limits of 0.06

lbs/MMBtu heat output.

(a) No person shall install or allow the installation of any outdoor pellet boiler that 

has been certified to meet a particulate matter emission limit of 0.06 lbs/MMBtu 

heat output, determined in accordance with Section 3(E) of this Chapter, unless 

the outdoor pellet boiler:

(1) has an attached stack with a minimum stack height of 10 feet above ground 

level; or

(2) has an attached stack extending two feet higher than the peak of the roof of 

the structure being served by the outdoor pellet boiler, if an abutting 

residence is located less than 100 feet from the outdoor pellet boiler.

(b) No person shall operate any outdoor pellet boiler, installed after the effective date 

of this Chapter, that has been certified to meet a particulate emission limit of 0.06

lbs/MMBtu heat output, determined in accordance with Section 3(E) of this 

Chapter, if an abutting residence is located less than 100 feet from the outdoor 

pellet boiler, unless the outdoor pellet boiler has an attached stack extending two 

feet higher than the peak of the roof of the structure being served by the outdoor 

pellet boiler.

(5) Outdoor wood boilers that have been modified to burn pellets. Outdoor wood boilers 

that have been modified to burn pellets must meet the applicable stack height 

specified in Section 3(C) of this Chapter for the original particulate emission limit 

certification of the outdoor wood boiler, determined in accordance with Section 3(E) 

of this Chapter.
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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(6) In the case that there is no structure (e.g. swimming pool or hot tub) being served by 

an outdoor wood boiler or outdoor pellet boiler subject to Section 3(C), the owner or 

operator of the outdoor wood boiler or outdoor pellet boiler shall extend the stack 

two feet higher than the peak of the roof of the nearest building to the outdoor wood 

boiler or outdoor pellet boiler.

D. Commercial Outdoor Wood Boiler, Commercial Outdoor Pellet Boiler, Outdoor 

Wood Boiler or Outdoor Pellet Boiler with a rated thermal output greater than 

350,000 Btu/hr Analysis Requirement

(1) Any person intending to install or operate a commercial outdoor wood boiler, 

commercial outdoor pellet boiler, an outdoor wood boiler, or outdoor pellet boiler

with a rated thermal output greater than 350,000 Btu/hr shall obtain an evaluation, 

report and installation recommendations performed by a qualified professional, 

including a licensed professional engineer or a master solid fuel burner technician,

that includes the following information:

(a) What type of application will the outdoor wood boiler or outdoor pellet boiler be 

used for;

(b) A determination of the heat load requirements of the facility as compared to the 

available heat supply of the outdoor wood boiler or outdoor pellet boiler to 

ensure the unit is properly sized;

(c) The stack location relative to the property lines and building locations within 400 

feet of the outdoor wood boiler or outdoor pellet boiler;

(d) The stack height; and

(e) Recommendations for the proper outdoor wood boiler or outdoor pellet boiler 

installation, including but not limited to, hook-up, auxiliary fuel, properly sized 

outdoor wood boiler or outdoor pellet boiler, stack height and stack location.

(2) No person shall install or operate a commercial outdoor wood boiler, commercial 

outdoor pellet boiler, outdoor wood boiler or outdoor pellet boiler with a rated 

thermal output greater than 350,000 Btu/hr unless it is installed according to the 

recommendations of the evaluation report in Section 3(D)(1). In any case, no person 

shall install or operate a commercial outdoor wood boiler, commercial outdoor pellet

boiler, an outdoor wood boiler or outdoor pellet boiler with a rated thermal output 

greater than 350,000 Btu/hr unless it meets the minimum setback and stack height 

requirements stated in Section 3(B) and 3(C) of this Chapter.

E. Certification of Outdoor Wood Boilers and Outdoor Pellet Boilers. No person shall 

supply, distribute, sell, lease, offer for sale, or allow the installation of an outdoor wood 

boiler or an outdoor pellet boiler in the State of Maine unless the outdoor wood boiler or 

outdoor pellet boiler has received certification pursuant to the EPA Outdoor Wood-Fired 

Hydronic Heater Program. The certification shall demonstrate that the outdoor wood 

boiler or outdoor pellet boiler meets the applicable particulate emission standard in 

Section 3(A) of this Chapter. The manufacturer of any such outdoor wood boiler or 

outdoor pellet boiler shall conduct testing via the EPA Outdoor Wood-Fired Hydronic 

Heater Phase I Program until EPA replaces the EPA Outdoor Wood-Fired Hydronic 
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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Heater Phase I Program with the Environmental Technology Verification Program. The 

Department may approve an alternative certification program.

F. Sell-through exemption for Outdoor Wood Boilers. No person shall sell or offer for 

sale any outdoor wood boiler with a particulate emission rate greater than 0.60 

lbs/MMBtu heat input as certified in accordance with Section 3(E) of this Chapter unless 

the outdoor wood boiler was purchased, paid for in full and received in the State of 

Maine before April 1, 2008 and the outdoor wood boiler meets all of the applicable 

requirements of this Chapter. Compliance with this Section must be demonstrated by 

keeping records of the purchase date and receipt date of their inventory as of the effective 

date of this Chapter. These records shall be kept for at least 5 years and shall be made 

available to the Department upon request. This exemption is effective until April 1, 

2009.

G. Labeling Requirements. New outdoor wood boilers and outdoor pellet boilers shall be 

labeled in accordance with the labeling requirements of the U.S. Environmental 

Protection Agency Outdoor Wood-Fired Hydronic Heater Program. Requirements of this 

program are located at www.epa.gov/woodheaters/index.htm.

H. Rain Cap Prohibition. No person shall operate a new outdoor wood boiler or outdoor 

pellet boiler using a rain cap unless this device is required by the manufacturer

specifications.

4. General Provisions and Requirements For All Outdoor Wood Boilers and Outdoor 

Pellet Boilers

A. Prohibited fuels. No person shall burn any of the following items in an outdoor wood

boiler:

(1) any wood that does not meet the definition of clean wood;

(2) garbage;

(3) tires;

(4) lawn clippings or yard waste;

(5) materials containing plastic;

(6) materials containing rubber;

(7) waste petroleum products;

(8) paints and paint thinners;

(9) chemicals;

(10) glossy or colored papers;

(11) construction and demolition debris;

(12) plywood;

(13) particleboard; 

(14) salt water driftwood and other previously salt-water saturated materials;

(15) manure;

(16) animal carcasses;

(17) asphalt products;

(18) materials containing asbestos;

(19) materials containing lead, mercury, or other heavy or toxic metals; and

(20) coal, unless the outdoor wood boiler is specifically designed to burn coal.
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B. Fuel Requirements

(1) No person that operates an outdoor wood boiler shall use a fuel other than the 

following:

(a) Clean wood;

(b) Wood pellets made from clean wood;

(c) Home heating oil in compliance with the applicable sulfur content limit, propane 

or natural gas may be used as starter or supplemental fuels for dual-fired outdoor 

wood boilers; and

(d) Other fuels as approved by the Department.

(2) No person that operates an outdoor pellet boiler shall use a fuel other than the 

following:

(a) Wood pellets made from clean wood;

(b) Corn; and

(c) Other fuels as approved by the Department.

C. Visible Emission Standard. No person shall cause or allow the emission of a smoke 

plume from any outdoor wood boiler or outdoor pellet boiler to exceed an average of 30 

percent opacity on a six minute block average basis, except for no more than two six 

minute block averages in a 3-hour period. Opacity under this subsection shall be 

determined pursuant to EPA Method 9 Visual Determination of the Opacity of Emissions 

from Stationary Sources (40CFR60, Appendix A).

D. Enforcement and Preemption. This rule is subject to enforcement pursuant to 38 

MRSA §347-A. Nothing in Chapter 150 may be construed as pre-empting any otherwise 

applicable, statute, regulation, local ordinance or otherwise applicable private common 

law cause of action.

E. Notice to Buyers

(1) No outdoor wood boiler or outdoor pellet boiler subject to the requirements of this 

Chapter shall be offered, sold, offered for retail sale, or leased within the State of 

Maine unless prior to any sales or lease agreement, the seller or dealer provides the 

prospective buyer or lessee with a copy of this Chapter and a written notice that:

(a) It is unlawful to burn garbage, treated or painted wood, plastic and plastic 

products, rubber products, yard waste, lawn clippings, glossy or colored papers, 

construction and demolition debris, materials containing asbestos, materials 

containing lead, mercury, or other heavy or toxic metals, plywood, particleboard, 

salt water driftwood and other previously salt water saturated materials, manure, 

animal carcasses, asphalt products, coal, unless the outdoor wood boiler is 
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Chapter 150: Control of Emissions from Outdoor Wood Boilers

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specifically designed to burn coal, waste petroleum products, paints, chemicals or 

any substance that normally emits dense smoke or obnoxious odors;

(b) Installation of an outdoor wood boiler or outdoor pellet boiler may be subject to 

other applicable State and local stack height and setback requirements;

(c) The applicable distance and stack height requirements provided in Section 3(B)

and 3(C) of this Chapter may not be adequate in some areas due to terrain that 

could render the operation of an outdoor wood boiler or outdoor pellet boiler to 

be a nuisance or public health hazard; and

(d) States the specific results of the average and maximum emission rates of 

particulate matter for the outdoor wood boiler or outdoor pellet in grams per hour 

per the testing determined in accordance with Section 3(E) of this Chapter and 

the average delivered heating efficiency as found in the test reports that were 

used for certification of the units or a statement that the outdoor wood boiler or 

outdoor pellet boiler has not been tested or certified.

(2) The written notice specified above shall be signed by the buyer or lessee at the time 

of purchase or lease to indicate receipt of notice. Said notice shall contain the names; 

addresses; telephone number of both the seller or dealer and the buyer or lessee; the 

location where the outdoor wood boiler or outdoor pellet boiler will be installed; and 

the make and model of the outdoor wood boiler or outdoor pellet boiler. The dealer 

shall keep these records for 5 years and provide them to the Department upon 

request.

F. Owner’s Manual. Each outdoor wood boiler or outdoor pellet boiler offered for sale or 

lease must be accompanied by an owner’s manual that shall contain all the information 

listed below:

(1) Thermal output capacity;

(2) Proper installation information;

(3) Operation and maintenance information to minimize emissions;

(4) Wood loading procedures, recommendations on wood selection, and warnings on 

improper fuels;

(5) Fire starting procedures;

(6) Proper use of air flow devices, if applicable;

(7) Ash removal procedures;

(8) For catalytic models, information pertaining to maintaining catalyst performance, 

maintenance procedures, procedures for determining catalyst failure or deterioration, 

procedures replacement, and information on warranty rights.

(9) Language stating: Improper use or failure to maintain the outdoor wood boiler or 

outdoor pellet boiler may cause nuisance conditions. Persons operating this outdoor 
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wood boiler or outdoor pellet boiler are responsible for operation of the outdoor 

wood boiler or outdoor pellet boiler so as not to cause a nuisance condition. Even 

proper use and maintenance of the outdoor wood boiler or outdoor pellet boiler, and 

meeting the distance and stack height recommendations and requirements in State 

and local regulations may not always be adequate to prevent nuisance conditions in 

some areas due to terrain or other factors.

5. Nuisance Conditions

A. Standard. No person shall operate an outdoor wood boiler or an outdoor pellet boiler, 

that produces visible emissions, measured as any opacity totaling twelve minutes in any

hour, that cross onto any land or buildings immediately adjacent to a dwelling or 

commercial building not owned by the owner of the outdoor wood boiler. Opacity under 

this subsection shall be determined pursuant to EPA Method 22 Visual Determination of 

Fugitive Emissions from Material Sources and Smoke Emissions from Flares (40CFR60, 

Appendix A).

B. Prohibition. No person shall operate an outdoor wood boiler or an outdoor pellet boiler,

in such a manner as to create a nuisance.

6. Third Party Sales

As of the effective date of this Chapter, an outdoor wood boiler or outdoor pellet boiler that 

has been owned by an individual and was in use in Maine prior to the effective date of this 

Chapter may be distributed or sold to another individual for his or her own personal use. The 

outdoor wood boiler or outdoor pellet boiler shall be subject to the applicable setback and 

stack height requirements specified in Section 3(B) and 3(C). If the particulate emission limit 

is not known, the outdoor wood boiler or outdoor pellet boiler must meet the setback and 

stack height requirements of Section 3(B)(1)and 3(C)(1).

7. Effective date

Unless otherwise noted, compliance with all applicable provisions of this Chapter is the 

effective date of the regulation.

8. Severability

Each Section of this Chapter shall be deemed severable, and in the event that any Section of 

this Chapter is held invalid, the remainder shall continue in full force and effect.

AUTHORITY: 38 M.R.S.A., §585-A, §610-B

EFFECTIVE DATE: November 9, 2007

 Amended: July 4, 2008

April 7, 2009

April 11, 2010

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BASIS STATEMENT

In 1988 EPA established particulate emission standards for residential wood stoves sold in the 

United States after 1992. However, outdoor wood boilers (OWB), also known as outdoor woodfired hydronic heaters (OWHH) were not included in the EPA residential wood stove regulations 

and have not been regulated by EPA or the Department. OWB, which burn wood to heat water 

that is piped underground to a nearby structure (usually a home) for space heating, are available 

in a wide variety of sizes and efficiencies. OWB, on an average per hour basis, emit about four 

times as much fine particulate matter as conventional wood stoves, about 12 times as much fine 

particulate matter as an EPA-certified wood stove, and 1000 times more than an oil furnace.

In addition to fine particulates, wood combustion emissions contain sulfur oxides, nitrogen 

oxides, carbon monoxide and potentially cancer-causing compounds including formaldehyde, 

polycyclic aromatic hydrocarbons, benzene and dioxins. Fine particulates can aggravate lung 

diseases such as asthma, emphysema and bronchitis. Children, the elderly and those with 

respiratory problems are most at risk from exposure to wood smoke.

In June 2007, the Maine Legislature enacted LD 1824, An Act To Regulate Outdoor Wood 

Boilers. This legislation established emission standards for new outdoor wood boilers starting in 

2008 and also directed the Department to adopt rules related to outdoor wood boilers. “The rules 

must include provisions relating to siting, operation and labeling requirements, stack heights, 

dealer and manufacturer reporting, public notification of emission standards and operation and 

siting requirements, code enforcement officer training, nuisance conditions and existing inventory 

issues.” 

Chapter 150 establishes requirements for the sale and installation of new outdoor wood boilers, 

including particulate emission standards and requirements for setback and stack height, 

certification, sell-through of existing inventory, and labeling. The rule also contains general 

provisions which apply to all OWB. These provisions include prohibited and allowed fuels, 

visible emissions standards, notice to buyers, and owner manual requirements. In addition, 

pursuant to the new legislation, for the purpose of this rule, the Department included a definition 

of “nuisance” and a method by which a nuisance condition can be identified. Pursuant to 38 

MRSA Section 610-B, Chapter 150 was adopted as emergency major substantive rules pursuant 

to Title 5, section 8073 and must be submitted to the Legislature for review by January 15, 2008.

BASIS STATEMENT FOR AMENDMENT OF MAY 15, 2008

In April 2008, the Maine Legislature enacted Resolve Chapter 190, Regarding Legislative 

Review of Portions of Chapter 150: Control of Emissions from Outdoor Wood Boilers, a Major 

Substantive Rule of the Department of Environmental Protection, Bureau of Air Quality Control. 

This legislation requires amendments to Chapter 150 in several areas: 1) clarifying that in order to 

be eligible for the sell-through exemption contained in the rule the outdoor wood boiler must 

have been purchased, paid for in full and in the State of Maine prior to April 1, 2008; 2)

authorizing the optional use of setbacks from neighboring dwellings for the installation of new 

outdoor wood boilers; and 3) requiring that setbacks from state licensed school, daycare or 

healthcare facilities conform to the general setback requirements.
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BASIS STATEMENT FOR AMENDMENT OF MARCH 19, 2009

In April 2008, the Maine Legislature enacted Resolve 2007, Chapter 190, Regarding Legislative 

Review of Portions of Chapter 150: Control of Emissions from Outdoor Wood Boilers, a Major 

Substantive Rule of the Department of Environmental Protection, Bureau of Air Quality Control. 

This legislation requires the Board of Environmental Protection to adopt rules by April 1, 2009 to 

control the sale, installation, use and siting at residences and businesses of outdoor wood boilers 

that combust biomass pellets as a fuel source. 

BASIS STATEMENT FOR AMENDMENT OF MARCH 18, 2010

In May 2009, the Maine Legislature enacted Public Law, Chapter 209 LD 1171, An Act to Amend 

the Laws Governing Outdoor Wood Boilers, which became effective September 12, 2009. This 

legislation directs the Department to amend the definition of commercial outdoor wood boiler, 

establish a voluntary technology-forcing particulate emission limit, amend the definition of 

outdoor wood boiler and change the qualifications for those who prepare an evaluation, report 

and installation recommendations for commercial outdoor wood boilers and larger outdoor wood 

boilers.

In addition to the basis statement above, the Department has filed with the Secretary of State a 

response to comments received during the comment period.