Vent-Free Heating – the Pro’s and the Con’s

I often get asked about the use of vent-free heating systems and their use as opposed to direct-vented systems. This may answer some questions.

New York State has recently approved vent-free gas heating appliances for use. However, it was only under intense lobbying from the vent-free stove and fireplace manufacturers that the measure passed, and I am concerned about the use of vent-fee or vent-into-the-room fireplaces and stoves for several reasons.

Vent-free gas appliances should be properly sized for the size and energy tightness of the space that they are to be used in. Bedrooms, basements, small confined areas, and tightly insulated homes are potential high-risk areas to be avoided.

Very specific installation and usage guidelines are required as part of the vent-free appliance sales process, yet some retailers have been seen to be far to lax in providing consumers with accurate usage information and warnings.

Persons with allergies, asthma, or a history of heart or lung problems should be especially careful, along with the elderly, infants, or pregnant adults to exposure to fumes from vent-free units. And, although a loosely insulated cottage could be outfitted with a vent-free unit with little concern, you still should be aware that these appliances are not designed to be a primary heat source or used continually. Four hours per day is a typical recommended maximum usage.

Gas gives off by-products when it burns, including carbon monoxide, nitrogen dioxide, carbon dioxide, and moisture vapor. Although vent-free units are touted as 99 percent efficient, these by-products, if allowed to build up in an enclosed space can cause harmful side-effects.

Vent-free devices have built-in safety devises that are designed to shut the appliance down in case of a malfunction or if combustion oxygen falls to dangerously low levels. Still, caution is advised.

If there are existing pollutants within the house such as formaldehydes that out-gas from man-made synthetic materials and dyes, additional chemicals may be discharged into the air as these burn and chemically sensitive persons may be irritated from the combustion process.

Dust and pet hair that get sucked into the unit and burn can cause sooting. And, if the appliance is not periodically cleaned and tuned, its efficiency may decrease over time, further adding to the pollution.

Of major concern is the addition of moisture vapor to indoor air while the vent-free unit is operating (up to a half-gallon per hour in some cases). Excess moisture within a closed structure can created problems such as mold mildew, and condensation staining as well as the more serious decay of wood members is unchecked.

It is often recommended that a window be left open during the use of a vent-free gas appliance to ensure a free flow of combustion air and to allow moisture vapor to escape the house. However, it should be obvious that opening a window will lower the efficiency of the unit and may create uncomfortable drafts.

It would be my recommendation to install a direct-vent or B-vented gas heater or stove. Installation should not be significantly more difficult that a vent-free model and you would have the peace of mind knowing that potentially harmful pollutants are being exhausted into the exterior. You will also be able to use the unit for longer periods of time, which will add to the comfort level and the enjoyment of your home.

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