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    To mitigate CO dangers, manufacturers instruct customers to keep a window open while ventless fireplaces are in operation –- advice that is easy to ignore, as an open window allows the entry of cold air, defeating the efforts of the fireplace to warm the living space. Many manufacturers also install an oxygen-detection sensor (ODS) in their ventless fireplaces that will automatically shut down the appliance if oxygen levels in the home become dangerously low. Critics point out that this sensor is typically located at the lower part of the unit near the floor, where it detects cool, fresh, oxygen-filled air and misses hot combustion gasses as they rise and pool toward the ceiling. And if the sensor fails, any CO-producing abnormality experienced by the fireplace will continue unnoticed and potentially harm building occupants.

   Massachusetts, California, and a number of other states in the U.S., as well as Canada and other countries, have outlawed ventless gas fireplaces due to the aforementioned safety concerns. Many individual municipalities, too, have outlawed these appliances in states where they are otherwise legal. The U.S. Department of Housing and Urban Development bans ventless fireplaces in their housing, and advisements against the use of these appliances have been issued by various watchdog groups, such as the American Lung Association, the Centers for Disease Control, the Environmental Protection Agency, and even the Mayo Clinic. In particular, these organizations warn against exposure of individuals who are particularly vulnerable to CO, namely, the elderly, pregnant women, small children, those with pre-existing cardiovascular difficulties, and small pets. To be fair, though, there have been no documented cases of fatalities caused by ODS-equipped ventless fireplaces, according to the U.S. Consumer Product Safety Commission.

   In summary, ventless fireplaces, while attractive and portable, suffer from a design flaw that may allow dangerous gases to enter the living space.

   By the way, not all fireplaces without chimneys are unvented. There is a type of manufactured fireplace, specifically for use with a gas log, that uses a blower to exhaust the combustions gases out a wall vent. More about manufactured fireplaces in a future blog.


While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
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