Gas fireplaces are very common in homes and becoming even more popular as people want the romance of a fire without the consequential wasting of energy typical of conventional fireplaces. These units can actually heat a home and in some small condos they might be the only heat source. There are lots of things to discuss regarding these units but this blog is only going to address the foggy look that the glass panel sometimes has and will have over time. Every time the unit is fired the small amount of moisture inside the unit and in the gas itself will condense on the cold glass. As the unit warms up this cloudiness disappears. However, this condensation is slightly acidic and actually "etches" the glass which results in the cloudiness that we see.
All attempts to clean the surface with household cleansers will be ineffective and can actually permanently disfigure the glass. This cloudiness must be "polished" off, and gas fireplace supply stores carry polishes specifically for this purpose. Instructions on how to remove the glass panel are permanently attached to the unit (required to be). The instructions can usually be found in the compartment under the unit. Great care must be exercised in removal of the panel and especially re-installing the panel. Panels that are not properly seated can lead to carbon monoxide entering the home and/or venting of hot gases that can melt control mechanisms etc.
Charles Buell
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WA State, Home Inspector Advisory Licensing Board