Before you buy a fireplace insert, you should understand the different venting
mehtods used for each type of fireplace. The word venting refers to the means a
fireplace insert uses to vent its exhaust safely from the room.
In the case of a vent free gas fireplace, exhaust is vented directly into the room. In a
vent free system, the consumption of gas is limited to a maximum of 40,000 BTU per
hour to help prevent the room from being “starved” of oxygen.
In a direct vent system, a double vent pipe is used (pipe within a pipe). The outer pipe
draws fresh air from outside to feed the combustion process while the inner pipe vents
out the exhaust from the combustion. This type of fireplace should be located on an
outside wall. This allows for a shorter and thus more efficient through the wall vent
A fully vented system, including a B-Vent system, uses either a masonry chimney or a
B-Vent.* Now that we touched on the three primary methods of venting, we can take
a closer look at the pros and cons of each.
Vent Free Gas Fireplace – As mentioned, a vent free system vents its exhaust directly
into the room. In other words, it does not use a chimney at all. As you can imagine,
this can cause a carbon monoxide concern as this system continuously uses oxygen
from the room it’s being used in.
For this reason, vent free systems are equipped with an oxygen detection safety pilot
which detects when the oxygen level falls below 18%. If this occurs, the gas will
automatically be shut off.
Pro: You can install them almost anywhere in your home. They are very efficient,
meaning you get almost 100% of the heat benefit from the fuel you are burning (the
heat is not escaping outdoors).
Con: You need to buy specific types of burners/log sets specially made for Vent Free
systems. You cannot burn wood in them nor regular vented log sets nor other
specialty vented products. If you have respiratory-related health conditions, you may
want to think twice before installing this type of system.
Direct Vent Fireplace – A direct vent system pulls fresh air in and sends its exhaust
out through a combined flu system. The flu pipe vents either out of the top or out of
the back of the fireplace, for versatility. The flu pipe generally exits through a side wall
in your room.
Pro: No chimney is required, so less expensive to install than a Fully Vented fireplace.
They are highly efficient and may be used as a gas wall furnace. If you like a fireplace
with a sealed fire box (because of children, cats, etc.) this style may work well for you.
Con: You can’t burn wood in it. They require specific types of burners and logs so you
cannot use specialty vented products in them. You are not supposed to burn them
without the glass cover attached, as this disrupts the air flow in the balanced vent
Fully Vented Fireplace – A fully vented system is what most of us think of when we
think of a traditional fireplace. Usually we think of a brick and mortar chimney, but a
fully vented fireplace can also incorporate a B-vent* flu (a double wall metallic pipe
that rises up from the fireplace and out through the roof) where air for combustion
comes from inside the room.
Pro: You can burn wood in it. You can purchase a model that helps to make it more
heat efficient by having a fire box “float” inside a second box so air can circulate
around the fire box and back into the room.
You can burn many kinds of vented fire logs and specialty vented fireplace products in
this style of fireplace.
Con: For a new fireplace installation, you may spend more money having a chimney
built than you would with the other styles. This style is less heat efficient than the
other two styles.
*A B-vent unit draws air from inside the home, through ports in the firebox itself as
opposed to a direct vent unit which draws air through a pipe from outside the home into a
Direct vent models are usually more efficient and safer for today's airtight homes, since
they do not use inside air or cause a conflict with range hoods and bathroom fans
circulating the same air.
B-vent units are generally less expensive to install, but are more sensitive to air flow
inside the home.
The Pros & Cons of Vent Free, Direct Vent and
Fully Vented Fireplace Inserts