Types of gas wall heaters

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Types of gas wall heaters
Independent health and safety studies advise against vent-free gas wall heaters. (Heizung image by nizo from Fotolia.com)

Gas wall heaters provide localised heat and a cost-effective alternative to central heating, especially when only small areas of your home need to be heated. Gas heat functions during an electric power outage and is fuel efficient. The by-products of gas combustion, however, are toxic and can compromise indoor air quality. Becoming aware of the benefits and drawbacks of vented versus vent-free gas wall heaters is an important part of making a safe and informed decision about how to heat your indoor space.

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Ventless Gas Wall Heaters

Ventless gas wall heaters do not take in exterior air to function, nor do they vent to the outside. Because of this, ventless heaters do not require the construction of a chimney or flue, can be less expensive than vented heaters and are energy-efficient. According to the Vent-Free Gas Products Alliance, a trade group representing the vent-free gas products industry, ventless heaters operate at 99 per cent efficiency. This efficiency, however, does not come without cost. The American Lung Association and Consumer Reports studies advise against the installation of ventless heaters, as their emission of toxic combustion by-products, such as nitrogen dioxide, carbon monoxide and other fine particulates, compromise indoor air quality to the extent that health can be negatively effected. Moreover, the burning of natural gas creates water. One ounce of water is produced per hour for each 1,000 BTUs burnt. Mold accumulation and soot stains have been reported by vent-free heater users.

Vented Gas Wall Heaters

Vented gas wall heaters pull air for combustion from the inside, but vent the toxic by-products of combustion to the outside via a chimney or flue. They must be placed in an area where a vent system already exists or a new ventilation system must be constructed. Because of their connection to a venting source, these heaters allow heat to escape, making them less efficient than ventless ones. Allowing heat to escape, however, also permits toxic combustion gases and water vapour to be expelled to the outside, rather than the inside, your space.


Ventless heaters built after 1980 have an oxygen-depletion sensor that will go off if oxygen in the room falls below 19 per cent. An oxygen-depletion sensor, however, will not detect levels of carbon monoxide and other toxins. Consumer Reports suggests that a vented gas heater always be your first choice. If you live with an existing ventless gas heater, however, a number of precautions should be observed to protect your health and safety. Ensure the ventless gas heater is not your primary source of heat; all major building codes classify ventless gas heaters as a supplemental, not a primary, heat source. Only use your ventless gas heater for a few hours at a time. Open at least one window near the appliance. Ensure your firebox and log set, via a certification label on the log set or the owner's manual, are compatible; not all sets are. Ensure your heater meets industry-established sizing guidelines available at the Vent-Free Gas Products Alliance website; too large a ventless heater in too small a space will exacerbate indoor air-quality issues. Lastly, always install a separate carbon monoxide detector in the area your ventless gas wall heater operates.

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