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Let's start with the definition...
A direct vent system is a sealed system which brings in fresh air from the exterior, mixes the air with gas and exhausts the combustion products to the exterior.
What does that really mean?
What this means is that unlike older models which used air from inside a building (we'll call it "room air") and mixed it with gas and vented that to the exterior, a direct vent system is sealed away from the room air and uses exterior air to mix with gas and create flames.
This system is therefore more efficient because it is not removing any of the already heated room air from the building (which would need to be replaced, usually from leaks in the building).
Here's a drawing I made of a direct vent fireplace (don't be cruel, the flames look almost real!),
Although this drawing is of a rear vent fireplace, the same concept applies to a top vent fireplace, a fireplace insert and a direct vent stove.
The simple steps of a gas fireplace or stove as related to the venting
1. The pilot is lit, creating a small flow of intake/exhaust
2. The main burner switch is turned on
3. Gas flows from the orifice(s) below the burner, pulling fresh air (the venturi effect) along with it through the burner
4. The gas/air mixture escapes from the burner and passes the pilot flame, which causes it to ignite
5. The exhaust created by burning the gas/air mixture is hot and moves through the inner exhaust pipe to the exterior of the building where it rises. The vacuum created by the heated air/exhaust moving out pulls fresh air in from the outside through the outer pipe, to the bottom of the fireplace
6. This process is now a continuous loop
So how does this fireplace heat my house???
Most direct vent fireplaces are about 80% efficient in steady state (when they've warmed up and stay on for a while), so that means if you have a 30,000 BTU fireplace you can expect about 24,000 BTU's of heat into your house.
The air in the room (which is coolest by the floor) passes underneath the metal box which houses the burner, rises up the back and comes back into the room from the top as heated air. If you have blower installed, that increases the speed at which this happens but doesn't necessarily increase the efficiency. What a blower does is to help distribute the heat more evenly throughout the room rather than having a large hot spot (no, not free wifi) around the fireplace.
The fireplace also produces radiant heat which passes through the glass face of the fireplace.
Now you know how a direct vent fireplace works! What next???
1. Tell all your friends (it makes excellent dinner conversation)
2. Figure out how many rooms you're going to put one in
3. Check out the selection of fireplaces, stoves and inserts at northcountryfire.com
4. Sit back and enjoy the simplicity and ease of your new gas fireplace
Thanks for reading, I hope you found this article useful. Cheers!