Environmental Engineering Reference
In-Depth Information
Table 3.1
Factors Contributing to Flue Gas Spillage and CO Poisoning in Residences
• Corroded, cracked heat exchangers
• Dislodged or damaged fluepipes
• Improperly installed fluepipes
• Changes in appliance venting (mechanical draft furnace combined with a natural
draft hot water heater)
• Inadequate combustion air/tight building envelope
• Exhaust ventilation competes with furnace/fireplace for air
• Downdraft in chimney
• Blocked chimney
ability of flue-gas spillage by backdrafting is less than in systems which use
natural draft.
A. Flue-gas spillage
Serious flue-gas spillage occurs in North American homes, with occasional
deaths and, more commonly, sublethal CO poisoning. Flue-gas spillage has
been reported with gas furnaces, gas water heaters, and wood-burning appli-
ances. It occurs in residences with aging or poorly installed or maintained
combustion/flue systems. Major causes and contributing factors of flue-gas
Flue-gas spillage occurs when upward airflow is too slow to exhaust all
combustion products. Under circumstances such as chimney blockage, flue-
gas flow is stalled, resulting in significant contamination of indoor spaces
and a major CO exposure risk. In backdrafting, outdoor air flows down the
chimney or flue and spills through the draft hood. Backdrafting can occur
when a house is depressurized by competing exhaust systems (e.g., fireplace
and furnace), when the chimney is cold, and under some meteorological
conditions. Backdrafting can be a significant problem in energy-efficient
houses where infiltration air is not adequate to supply the needs of mechan-
ical exhaust systems, fireplaces, and furnace/hot water heating systems. This
potential problem is being addressed in building codes which require that
sufficient combustion and makeup air be provided by contractors.
B.
Wood-burning appliances
Wood-burning appliances, such as fireplaces and stoves, have a long history
in North America. The popularity of wood-burning appliances re-emerged
in the 1980s in response to increased energy costs associated with the rising
price of petroleum (which occurred as a result of military conflicts in the
Middle East). An estimated 5 million wood-burning stoves were being used
in the U.S. to provide supplementary space heating. Wood-burning furnaces
were also being used to provide whole-house heating as well.
Wood-burning appliance use in the 1980s was based on the premise that
energy costs could be reduced by setting back thermostats and spot heating
