LEARNING THE LINGO

VENT FREE UNITS CANNOT BE INSTALLED IN SLEEPING QUARTERS.
Vent Free gas logs are called just that, gas logs, not an insert. When you are looking to replace your vent free gas logs, it is important to have the inside dimensions of your fireplace,(See example to the right), when choosing the correct size log set.
With vent free logs, you can only burn the set 2 to 3 hours at a time without opening up window, door, or the damper on your fireplace if you have one. These units rely on indoor air for combustion and emits it back into the room.
These units should not be used a a secondary heat source and should not be run continuously.
A Vent Free INSERT is a complete unit that is inserted into a pre-existing masonry fireplace or pre-fabricated wood burning fireplace.
Regarding Vent Free Freestanding Gas Stoves, the same burn time is applied. You may only burn the stove 2-3 hours at a time without opening a window or door nearby.
Vent Free fireplaces may be installed with designated framing.

Unnatural/unattractive flame appearance
6,000 - 40,000 BTU limit
Burners are pre-assembled and cannot be modified
Logs must stay in the predetermined arrangement to prevent flame impingement
More installation restrictions
Sensitive to those with severe allergies and chronic lung conditions. Minimal exhaust remains in the home after combustion
Produces an odor while burning and intensifies odors already present in the living space (air fresheners, incense, dust, pet dander, etc.)
Increases humidity levels in the home
Can cause lung irritation.

Vented gas log sets are made to be used in an existing wood burning fireplace with a fully operational chimney and serve as a replacement for real wood logs. They feature lifelike detailing and produce tall, golden flames to create the illusion of an authentic wood fire.
Vented gas logs must be used with a functional chimney and require the chimney damper to stay open at all times to prevent the build-up of harmful combustion byproducts, like carbon monoxide.
Since the chimney damper is required to stay open, almost all of the heat produced is lost through the chimney, making Vented logs an incredibly inefficient source of heat.
Burners for Vented gas log sets either come standard or ANSI certified. A standard burner is assembled after you receive it and an ANSI certified burner is assembled at the factory, then tested for safety and efficacy.
Certain cities may require you to have an ANSI certified burner.

Direct Vent can be used as a primary heat source.
Horizontal or vertical termination
No air from inside the dwelling is used for combustion.
You can point a direct vent chimney in almost any direction.
Direct Vent can be operated with a wall switch/thermostat and remote control.
Direct Vent is the product of choice in most cold climates.
Direct Vent Units must always have a sealed glass front. This will produce radiant heat even when the power is lost in the home thus rendering the blower inactive.

A pre-fabricated open faced wood burning fireplace is nice if you just want to relax and hear the crackling of the the fire, but they are not very efficient. If you decide you want more heat in the future, a lot of pre-fabs are not approved for wood burning inserts, so you might want to consider before deciding.
You might want to consider a high efficiency wood burning fireplace. They can produce enough heat to actually heat your entire home.
Wood burning free standing stoves are another alternative to heating your house. They take up less room and most are 75% effiecient.
Efficient stoves do not work like Grandma's. They require a little more attention and preparedness for the efficiency that they will achieve.
Each manufacturer has specific instructions on break in procedures to ensure the stove works as efficiently tested.
https://www.epa.gov/sites/production/files/documents/dirtysecretbrochure2011_0.pdf
https://www.epa.gov/burnwise/choosing-right-wood-burning-stove