One cause of carbon monoxide poisoning from unvented heaters– incomplete combustion caused by lack of air–has been virtually eliminated in newer heaters by use of Oxygen Depletion Sensors (ODS). When properly maintained and adjusted, gas heaters produce low amounts of carbon monoxide. CO poisons more people than all other poisons combined. What about carbon monoxide risks? CO, a colorless, odorless, tasteless, non-irritating poison, is highly toxic and can cause death or permanent brain and organ damage. Carbon monoxide (CO), a toxic gas formed if combustion is incomplete.Carbon dioxide (CO 2), a non-toxic gas formed during complete combustion of carbon based fuels.What pollutants are released into a room when an unvented heater is used? The main combustion products formed when gas burns are: Providing 1 ACH to a 10 x 20 foot room in Iowa would require over 1,000 Btu/hour, which is over 25% of the output of a 3800 Btu/hr heater. The National Fuel Gas Code, commonly used in determining outside air requirements, is based on 1.0 air change per hour (ACH). Heating cold outside ventilation air reduces the thermal efficiency of the heater. The additional ventilation needed to reduce pollutants to tolerable concentrations depends on the tightness of the building and the health of the occupants. Once combustion pollutants are in the house outside air must be provided to dilute and remove the contaminants. Unvented heaters release pollutants into the house. To prevent wet windows and walls, the vapor must be prevented from condensing, reducing the maximum efficiency of the heater to 90.4 percent. With an unvented heater, the water vapor condenses on room surfaces, which increases the potential for wood rot, peeling paint, plaster failure, and mold growth. To recover this heat, the water must be condensed. Approximately 9.6 percent of the heating energy available in gas comes from burning the hydrogen which produces water vapor. How efficient are direct vent heating appliances? While the flame burns with over 99 percent efficiency not all the heat is available. Sizes range from under 5,000 Btu/hour to over 38,000 Btu/hour. Available styles include cabinet mounted units, wall mounted units, fireplaces, and fireplace inserts with a variety of flame patterns including blue flame, infrared, yellow flame, and glowing logs. Optional blower kits and ductwork allow them to heat two or more rooms. What types of vent-free heating appliances are available? Small portable units for use in a single room are manufactured for emergency heating–others are made to serve as a permanent heat source. Many heaters are designed to create a comfort zone in a single room, reducing heating costs. In most locations in the country gas is a relatively inexpensive fuel. Most are quiet, easy to use, and efficient. Many heaters do not require electricity allowing them to be used for emergency heat. What are some of the advantages of vent-free heating products? Because no vent pipe or chimney is required vent free heaters are easy and inexpensive to install.
In some areas state and local codes regulate unvented heaters. While convenience is the major advantage of vent-free gas heating products, the degradation of indoor air quality is a concern. Typical fuels are natural gas and LPG (propane). Combustion products are discharged into the heated space rather than exhausted to the outdoors through a chimney. An unvented heating appliance, also called a vent-free appliance, has no chimney vent and is located in the space being heated.
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