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Gas Fired Ventless Fireplace

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When VF logs are installed into a fireplace, the log mfr. typically requires the Fp meet the building code or NFPA 211 in the absence of a local bldg code. That would take care of the hearth extension. In addition, VF have a markedly increased clearance requirement over the header since that's where most of the heat is. A mantel that meets clearance for wood burning typically requires a 4" canopy or hood to push the heat well away from the facing.

On a listed VF enclosure with VF logs, you'll need to refer to both the log mfrs. instructions as well as the enclosure listing. These logs project a lot of radiant heat onto the floor. The listing allows for a max. temp. rise of 117F above ambient, which then determines the level of floor and mantel protection or clearances. The position of any gas logset can have a major impact on the radiant heat to the hearth extension. Too far forwards can overheat the HX as well as the header.


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Thanx....too easy....I was thinking it was something like "vitrified foam", or some highly technical material composition.

Chimney Bob calls these things "Room Vented Lung Filtered" appliances. I turned the thing on and about a 1/2 hour later everyone had a headache. I gave them an object lesson in why they should get rid of them.

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I write them up every time. There's an oxygen sensor that shuts it down if the O2 gets depleted but there's no integrated CO detector so it can still kill you. You'll neither see it nor smell it. Store-bought CO detectors don't work well enough to protect you.

The negative consequences are so great and the defenses so few.

Room vented, lung filtered...I'm gonna use that.


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An Oxygen Depletion Sensor or ODS safety pilot is nothing more than a finely tuned pilot designed to dropout at 18.5% ambient O2. Basically, the low O2 slows the flame speed sufficient to advance the pilot flame past the thermocouple to the point it drops out. ODS pilots are not field serviceable except cleaning them. You cannot replace just the thermocouple or adjust the bracket. You cannot ream out the orifice since it is an industrial ruby shot with a laser such that it resembles a spider web or snowflake. Should a plumber insert a drill bit to "clean it out", the ruby will shatter ruining the pilot.

I call these "lung vented" appliances. While the CPSC does not have a documented death from CO generated by an ODS equipped appliance, the can and do emit significant pollutants including para and acetylaldehyes, nitrogen oxides and odors. Stats are not kept on how many people get sick from these things. FYI, the ANSI std. allows a max. of 200 ppm air free from ventfree appliances.

Most of these units are grossly oversized for the space and construction. They must be kept meticulously clean and logs in the exact correct position per mfr.

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