Actually, NE IA Dave, running an unvented heater has EVERYTHING to do with condensation on tools, and moisture in the building.From your own Iowa State University: "How efficient are direct vent heating appliances? While the flame burns with over 99 percent efficiency not all the heat is available. Approximately 9.6 percent of the heating energy available in gas comes from burning the hydrogen which produces water vapor. To recover this heat, the water must be condensed. ******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 prevent wet windows and walls, the vapor must be prevented from condensing, reducing the maximum efficiency of the heater to 90.4 percent. Unvented heaters release pollutants into the house. Once combustion pollutants are in the house outside air must be provided to dilute and remove the contaminants. The additional ventilation needed to reduce pollutants to tolerable concentrations depends on the tightness of the building and the health of the occupants. Heating cold outside ventilation air reduces the thermal efficiency of the heater. The National Fuel Gas Code, commonly used in determining outside air requirements, is based on 1.0 air change per hour (ACH). 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." With an UNVENTED heater, air exchange in the room is recommended, which obviously cools the room, and reduces efficiency. SO, why not just run a VENTED heater in the first place!
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