Outdoor Hydronic Heater Regulation
Background
Outdoor hydronic heaters (also known as “OHHs” or “outdoor wood-fired boilers”) are
located outside the buildings they heat in small, insulated sheds with short
smokestacks (usually six to ten feet tall). They burn wood to heat water that is piped
underground to provide heat and hot water to occupied buildings, and sometimes also
heat greenhouses, swimming pools and similar structures.
Outdoor hydronic heaters can produce heavy smoke and release it close to the
ground, where it can linger and expose people in the area to health risks and nuisance
conditions. Wood smoke contains particles of varying sizes and a variety of toxic
substances (including carbon monoxide, formaldehyde, benzene, naphthalene, and
poly-aromatic hydrocarbons).
Particles that are 10 micrometers in diameter or smaller can pass through the throat
and nose and enter the lungs. Fine particles, which are 2.5 micrometers in diameter or
smaller (which are found in smoke), can penetrate deeply into the lungs and
accumulate in the respiratory system. Particles have been linked to a number of health
effects, including decreased lung function, increased respiratory irritation, aggravated
asthma, chronic bronchitis, irregular heartbeats, heart attacks and premature death in
people with heart and/or lung conditions. In addition, wood smoke contributes to the
formation of haze that obscures visibility over large areas or regions.
Outdoor hydronic heaters are designed to burn dry, seasoned wood. However, some
people have burned green wood (which increases smoke generation) and household
trash or construction debris (which releases a harmful array of chemicals and is also
prohibited by state law). Even when these units are operated according to
manufacturers' instructions, they may create nuisance conditions that are prohibited by
state air quality regulations.
MassDEP regulations governing OHHs take effect on December 26, 2008 to ensure
that these units burn only clean wood, minimize their impact on air quality in the
Commonwealth, and do not create air pollution problems for their neighbors. The
regulations establish a stringent limit on total particle emissions from new units, and
requirements for their location and operation. The regulation also limits operation of
existing units to the winter heating season if they are close to other buildings and have
short smoke stacks.
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