These fires work in a very similar way to Conventional flue High efficient gas fires, as they have a glass front allowing a slower movement of air, a convector box allowing convected heat to warm-up through the convector channel and heat the room, along with radiant heat from the heated ceramics. But has one main difference, it doesn’t need a chimney. Balanced Flue Gas Fires have a unique way of venting any fumes by exiting through a wall to the outside. There are several different ways of doing this, as seen on the left via two pipe one at the top venting exhaust and the lower one providing fresh air into the burner to supply oxygen to the flames, or through a twin walled system shown on the right, this uses one pipe inside of another, the internal pipe used to exhaust hot fumes, which in turn warms up the fresh air coming in through he exterior pipe allowing a higher efficiency as the air is pre heated ready to burn. The latter flueing system of the twin wall pipe work also allows much flexibility when it comes to installation, as you can allow several bends and extensions should you be limited with the suitability in your home. This also offers several large glass windowed products along with two sided glass fronted fires which can be used as room dividers along with many other extravagant designs to choose from the best selling being Drugasar, a Dutch make who are adamant they will produce a product of high quality in a high class design (n.b there are several things which must be taken into consideration when designing your flue system always consult a Gas Safe Registered installer before purchase)
Efficiency of Balanced Flue Gas fires is usually limited to upto around 86% as the exhausting system does allow a vacuum like airflow through the item due to the fire having an open flue to the outside. The benefits of the flue flexibility and designs available I don’t think we have to care too much about a loss of 4%. As they are sealed units they will not require a vent in the room.