To Vent or Not to Vent – That is the Question

Kington direct vent insert by Hearthstone

By Marge Padgitt


Many homeowners end up asking chimney sweeps to take out their vent-free gas logs due to problems they find associated with the appliance. People have experienced a horrible odor when the logs are in use, water running down the windows and walls, stains and soot on walls, baseboards, and ceilings, mold and mildew issues, unexplained headaches, and being ill while in the house while using the logs. 

When burning gas several by-products of combustion are produced: Carbon Monoxide, Carbon Dioxide, Nitrogen Dioxide, Formaldehyde, and significant quantities of water.

Manufacturer instructions say to use non-venting gas logs four or less hours per day and to operate the logs with a window open.  Since these are listed as heating appliances and most customers purchase the logs as a heating source, this seems impractical in the middle of winter.  The American Gas Association Research Division (AGARD) recommendations for proper usage of a vent-free appliance include that the appliance is not to be used as a sole source of heat or in confined spaces or bedrooms. What happens when there is a power outage?  Homeowners are tempted to use the logs continuously, which can be a fire hazard. 

During the combustion process moisture is created. When a 40,000 BTU vent-free appliance is used to heat it can produce over six gallons of water a day.  If the homeowner notices condensation on windows and walls the vent-free appliance may be the cause.  We call these appliances “Room Vented” for this reason.  The condensation will be absorbed by the drywall, wood flooring & furniture, and may cause structural damage to the home. The excessive moisture may cause mold and mildew which creates problems for people with allergies, asthma, and other respiratory problems, or create new health problems. 

The situation is worsened in tightly constructed homes without adequate make-up air to provide air for the appliances, and for people to breathe. This issue is one that the HVAC and chimney industries contend with on a daily basis.  It is estimated that at least 80% of homes need a make-up air source such as a whole-house ventilator. If a problem exists before an appliance is installed, it is only going to get worse. 

Carbon Monoxide is a very real issue.  CO is always produced during combustion, and with room-vented heaters CO is vented into the room at so called “acceptable' levels. Even at low levels not registered with CO detectors, CO can be dangerous to children, pregnant women and their unborn babies, small children, the elderly, animals, birds, and people with upper respiratory conditions.  See Dr. David Penny's website at www.coheadquarters.com for more information about Carbon Monoxide.

Direct Vent Gas Appliances:Most professional chimney sweeps suggest installing a direct-vent type gas log insert or fireplace.  These types of appliances are vented through the wall or up an existing chimney. They are sealed systems which use outside air for combustion, thereby increasing the efficiency of the appliance and eliminating the need for opening windows while the appliance is in use. No by-products of combustion are vented into the room, so toxic gasses and water are vented directly to the outdoors.  Direct-vent, therefore, is a much better choice. 

Vent-Free VS Direct-Vent

Vent-Free VS Direct-Vent	Vent-Free	Direct-Vent
Must operate with window open	Yes	No
Has its own combustion air supply	No	Yes
Is a High-efficiency appliance	Yes	Yes
Gasses vented into the room	Yes	No
Moisture/water vented into the room	Yes	No
Can produce bad smells	Yes	No
Should have an annual service check-up and cleaning	Yes	Yes
Can be used in a masonry chimney	Yes	Yes
Can be used in a manufactured fireplace	No	Yes

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Marge Padgitt is a 30-year industry veteran, CSIA Certified Chimney Sweep and NFI Certified Woodburning Specialist and trainer. She is the president of HearthMasters Education, HearthMasters, Inc. and Padgitt Forensic Investigations in Kansas City, Missouri. Contact her at margepadgitt@comcast.net or chimkc.com or hearthmasters.net.