Gas fireplaces need to properly vent unwanted by-products of combustion to the outdoors.

 

When propane or natural gas mixes in the right ratio with oxygen, and it is combined with an ignition source, a chemical reaction takes place. This reaction produces the heat we enjoy, but it also creates some unwanted by-products such as carbon monoxide and water vapour. These must be vented outside.

 

Except for log sets, fireplaces may be gravity vented, direct vented or power vented.

A gravity-vented appliance is connected to a vent that takes the products of combustion out of the house.

 

The vent is powered by 'waste' heat.

 

Some heated room air is lost with a gravity vent.

 

If there is a strong flow of cold outside air down the vent on start-up, the appliance may 'back-vent' continuously, sending the combustion products into the house. This can be avoided by opening a window or outside door, at the same level as the fireplace or lower, for a short time when the fireplace is started.

A direct-vented fireplace can be more efficient because it doesn't use room air for combustion or allow any room air out through the vent. All the air it needs goes straight in and straight out of the vent.

 

The venting may be straight through the outside wall, or it may extend for a limited distance horizontally or vertically through the house. The vent terminal must be level with or higher than the top of the fireplace.

A power-vented fireplace has a fan that removes the combustion by-products through a vent to the outside.

 

The vent terminal may be above, level with or below the fireplace. A power-vented fireplace can be used where other venting options aren't practical. However, it can not be used during a power failure.