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Vent-free Gas Appliances - Our Opinion

Q: I notice you don't feature any vent-free gas stoves, gas logs or fireplaces on your website. Are you prejudiced against them because you're a Chimney Sweep and they don't need chimneys, or what?

Sweepy  Before the term "vent-free" was coined, these appliances were known by the more accurate but less friendly-sounding names, "unvented" or "room vented". Vent-free gas stoves, gas logs and fireplaces don't have chimneys because their exhaust vents into the breathing space of the home instead of outside.

Vent-free gas stoves, gas logs and fireplaces are a very controversial subject. On the plus side, they are easier and less expensive to install, because they don't require installation of exhaust venting to the outside. On the minus side, many scientists and medical professionals are concerned about health problems that derive from breathing gas exhaust.

At this writing, unvented gas stoves, gas logs and fireplaces have been outlawed altogether in Canada, Australia, and New Zealand. In the US, it is illegal to install vent-frees anywhere in the States of California and Montana. Minnesota has a state-wide ban prohibiting installation of vent-frees in any home built after 1980. County-wide bans exist in several states, including Arizona, Colorado, Washington, Kansas, Wyoming, Ohio, Michigan, North Dakota, South Dakota, Nevada, New Mexico, Alaska, Minnesota, Texas and New Hampshire. Austin, Texas and New York City have outlawed vent-frees on a city-wide basis. Most areas that don’t ban vent-frees altogether prohibit their use as the sole source of heat in any dwelling.

Washington State has taken a hard look at indoor air quality in recent years, and passed legislation designed to make the breathing environment in our homes healthier. One of the issues this legislation addresses relates to fuel-burning heaters. Studies have revealed that people who have wood, gas and oil-burning appliances in their homes live in an oxygen deprived environment all Winter. This has been linked to a number of health problems, including an irreversible lowering of white blood cell count. Today, all new heating appliance and fireplace installations are required by Washington State law to draw their combustion air from outside the home. Washington State has yet to adopt a statewide policy regarding vent-free appliances, which not only take their combustion air directly from the room, but vent gas exhaust into the breathing space: however, popular opinion seems to be that vent-free appliances will be banned here.

We have followed the vent-free debate closely for some time now. We finally decided not to sell vent-free gas appliances, for several reasons:

(1) Aside from the unpleasant exhaust odor and the possibility of coating your entire house with black carbon deposits when they need cleaning or go out of adjustment, vent-free appliances are considered by many medical professionals to be a health hazard. Indoor Air Quality scientists have warned that these heaters produce enough pollutants to make building occupants sick. There have been documented cases involving symptoms associated with low level CO poisoning in homes where vent-free gas appliances are used.

(2) Along with carbon monoxide and carbon dioxide, gas exhaust contains nitrogen dioxide, which combines with water to form nitric acid: Proponents of vent free gas appliances recommend an allowable indoor nitrogen dioxide concentration of 0.5ppm, despite the fact that international, federal, and state agencies have reported that a concentration of only half that amount (0.25ppm) can quickly result in unacceptable indoor air quality.

(3) All parties to the debate agree that sizing vent-free heaters correctly for the amount of ventilation in the home and for the local climate is an important element in safe operation. The problem with sizing guidelines is that they are difficult to follow, since installers don't have the necessary air infiltration and ventilation information available for a given house. In addition, air quality officials have no way to ensure that a window is open during operations, or to monitor the maximum time these heaters are in use every day.

(4) Vent-free gas appliances can also create an uncomfortably humid indoor environment. A 40,000 BTU vent-free fireplace will exhaust a gallon of water vapor into the house every 2-1/2 hours: disgruntled hearth product dealers who have sold vent-free appliances report customer complaints of dampness, slimy walls, mildew, mold, and peeling wallpaper.

(5) Vent-free appliance manufacturers typically include a statement in the owner's manual requiring that a nearby window must be opened whenever the appliance is lit. Their claims of 90+ percent heating efficiency don't take into account the fact that the homeowner is required to provide an open passageway to the outdoor cold whenever the fire is going.

(6) In order to limit occupants' exposure to the poisons contained in gas exhaust, manufacturers of vent-free appliances must tune them to burn with the lowest possible emissions, which makes the flames appear small and bluish. This is a far cry from the comforting, natural wood fire look that can be achieved in vented gas appliances.


Read about how much CO2 a vent-free fireplace exhausts into the breathing space

Read about a recent study of the effects of long-term exposure to CO gases

Read about respiratory irritation from vent-free exhaust in the breathing space

Read a posting about vent-free gas appliances from an indoor air quality scientist

Read what Consumer Reports Magazine has to say about vent-free products

Read letters in defense of vent-free products

Read about a 2016 ASHRAE standard that could eliminate the entire vent-free product category in the US

Have a vent-free experience you'd like to report?  Here's a link to the Consumer Product Safety Commission website.


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