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
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 pipe.
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
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 system.
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 sealed firebox.
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