To understand whether a fireplace is harmful to the environment or not, you should focus on the fuel type. The open fires are one of the least eco-friendly combinations; it requires poor quality solid fuel to run, which releases a lot of smoke.
If you’re burning wood, then it’s not necessarily harmful to the environment. But, you should only burn well-seasoned wood in a sealed glass fronted appliance (e.g., stove). This is a carbon-neutral way to heat your home. However, when these measures are not taken up, your fireplaces can pose a threat to the environment.
The efficiency rating of an open fire is just 30%, with the maximum amount of heat rising up the chimney. You should avoid burning dirty coal or wet wood, as it produces high levels of smoke, which leads to environmental damage, health problems, and air pollution.