What is the primary concern regarding ventless gas fireplaces?

The primary concern regarding ventless gas fireplaces is carbon monoxide exposure. These fireplaces operate without a chimney or flue, which means that combustion gases, including carbon monoxide, can accumulate inside the room where the fireplace is located. Inadequate ventilation can lead to increased levels of carbon monoxide, which poses serious health risks, including headaches, dizziness, and in severe cases, even death.

While other factors such as cost efficiency, environmental impact, and design flexibility are important considerations when choosing a fireplace, they do not pose the same immediate and life-threatening risks associated with carbon monoxide exposure. Therefore, the focus on safety and health makes carbon monoxide a critical concern for the use of ventless gas fireplaces.