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Open damper, closed damper?


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I understand that when gas logs are placed in a fireplace the damper should be equipped so that it cannot be closed. But I'm told that ventless gas log systems should have the dampler closed. Is this true, and if so, is there a way to tell the difference between a vented and ventless gas log system by looking?

Thanks for your help.

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Tim,

If it's a true ventless unit, there will not be a damper. If someone is saying that a damper firebox can be used at ventless it's wrong. Ventless appliances use specific burners that would not be used in vented applications. All manufactured fireplaces should be used only as they were designed and tested for - no modifications.

Does this help?

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Originally posted by Eric B

Tim,

If it's a true ventless unit, there will not be a damper. If someone is saying that a damper firebox can be used at ventless it's wrong. Ventless appliances use specific burners that would not be used in vented applications. All manufactured fireplaces should be used only as they were designed and tested for - no modifications.

Does this help?

Eric, yes that helps. The Code Check 5th Edition says under "Fireplace with gas appliance": "Decorative log set requires damper blocked open" And "Unvented log heaters not in factory fireplace unless L&L." I was just a little unclear about what that actually required.

Tim

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Originally posted by msteger

But how does one burn a fossil fuel without producing any byproduct exhaust? A 'Ventless fireplace' sounds like an oxymoron.

We have to remember that carbon monoxide is an emission from incomplete combustion of the fossil fuel. True combustion should only produce carbon , hydrogen and oxygen (C and O combine to produce CO2 - carbon dioxide, H and O combine to create h2o- water).

Pure combustion of natural gas and propane produces a blue flame, incomplete combustion produces yellow or orange flames.

The hydrogen atoms are easiest to satisfy and will be greedy and be satisfied first by attaching themselves to an oxygen atom (2 hydrogens/1 oxygen) this will fill all of the atomic rings and satisfy all of the hydrogen atoms released, creating water.

The carbon atoms left over because they were not all burned up will start grabbing the left over oxygen molecules trying to create co2, but being a friendly bunch, they do not want to be stingy and therefore share the oxygen atoms so that they can all get slightly satisfied, instead of simply gorging themselves until they are stuffed. Since the carbon was not completely, there will be an excess of carbon atoms and not all will be satisfied. The resulting molecules will be carbon with one oxygen (CO) and in severe cases, pure carbon (soot).

CO2, and H2O from complete combustion are relatively harmless in low or normal concentrations.

CO, on the other hand, is dangerous in low doses because our bodies will absorb it before oxygen even when oxygen is present.

A vent less fireplace uses a catalyst plate (like the calytic converter in your car's exhaust) which increases the temperature of the flue cases to a point that the carbon atoms are more thoroughly burned up. This allows what little carbon that remains to fill itself with oxygen and become carbon dioxide.

Regardless, I always highly recommend a CO detector in the home. Catalyst plates can and do get coated and need replacement over time.

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