I inspected a Superior fireplace with gas and with a direct vent to the exterior rear wall.

The glass was cloudy, fogged up, and there was rust inside of the firebox at several locations. What would cause the fog? I'm suspecting somehow there is condensation buildup in the firebox which is rusting the metal components..just not sure why the condensation would occur or why the glass is fogged up.

Any ideas?

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When you burn natural gas, water vapor is a combustion byproduct. All you are seeing is minerals and such from the water vapor that are deposited on the glass. You can remove the glass front and clean it off pretty easily, FTR.

But wouldn't the condensation be a defect, meaning the vent isn't operating properly. It certainly is causing rust in the firebox which I think is worthy to put in the report, don't you think?

brianmiller,

Kevin is correct with one exception. Depending on the content of the gas, sometimes the glass ends up being etched. This condensed moisture is somewhat acidic and it is likely contributing to the corrosion in the firebox. The rust would concern me, depending on how much there is. I would get an appropriate technician in there to ensure that it is burning and exhausting correctly.

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The condensation occurs upon start up -- then the heat burns off the moisture, leaving the deposits behind. While the vapor is slightly acidic, I have a ten year old FP of that type and I've cleaned it repeatedly with no etching. If the rust isn't simply from construction, i.e., a firebox installed prior to having a functional roof, then the cause should be investigated. Unbelievably, I once found a brand new home with the combo air inlet/exhaust installed upside down. But around here, I see plenty of them that are put in early enough that they get rained on.

I have a similar comment for these fireplaces that I do for forced air furnaces. Basically, that most manufacturers recommended annual service and the seller should provided documentation of a recent service or it should be checked by a qualified installer or contractor.

I think the majority of owners never have these fireplaces looked at.

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All direct vent fireplaces' glass fogs up with water vapor condensation when you first fire them up. It burns off in a few minutes. During combustion, a witches brew of acids, moisture, and silicone from sealants combine to form the white haze or film on the glass. If you clean it right off, the glass may last 20 yrs. Leave it unattended and it can become translucent within one to two seasons. Regular glass cleaners cannot faze it. You need a micro-abrasive. The industry std. is called "White Off" made by Rutland. You can also use Cerama-Bryte which was made for ceramic glass cooktops. Heatilator tested Brasso and Noxon metal polishes and approved them, too. Out techs used Brasso and it works well. You put some on a clean cloth and grind away in circles--wax on/ wax off. Once the crud is loose, you clean it all off with regular glass cleaner. Do NOT use Soft Scrub as it is too abrasive and will ruin the glass. Also, no razor blades. Keep all diamond rings and sharp hard points such as the corner of a raise brick hearth extension clear, too. You don't want 40K Chicklets all over the floor when the glass shatters.

The most important thing is to let the glass cool prior to cleaning, esp. std. tempered glass. If you spray cleaner on hot glass, you can shatter the glass, create stresses that lead to later shattering or take the temper out of the glass by annealing it. You can usually tell if this happens by the rainbow coloration on a section of the glass. If you see glass that has a rainbow, scratches or 10 y/o crud, it's probably time for new glass. Also, some units have defective gaskets its all the more reason to get a qualified tech in there to check the unit out and test the seal during firing.

HTH,
Bob

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