While a hot fire can help heat up and loosen tar within your chimney, making it a recommended step before using a creosote log, it will not burn off significant existing buildup on its own. Attempting to remove built-up creosote with a hot fire is dangerous and can cause a chimney fire. For safe and effective removal of caked-on creosote, the best approach is to hire a professional chimney sweep.

Generally, an oil furnace is considered safer than a gas furnace for several reasons. While both types of furnaces can produce carbon monoxide, a leak in an oil furnace is easier to detect due to the smell. Oil furnaces also don't connect to a gas pipeline, which reduces the chance of a fuel leak. Most importantly, heating oil is not combustible, whereas natural gas is highly flammable. This means there is a much lower risk of combustion or explosion with an oil furnace. However, an oil furnace can still pose a fire hazard if it tips over.

There aren’t many problems with fire doors except that they slow down or cut off ventilation at the higher rating levels. For this reason, work with a professional to ensure you have adequate ventilation throughout your house or workspace. The sealing around a fire door is meant to allow for a specific amount of ventilation and will need regular inspections to ensure adequate airflow.

The short answer is yes, but the longer answer is more complex. Unless the fireplace is ventless by design, you’ll need some type of exhaust pipe system to safely send fumes and other harmful byproducts out of the house. Even then, ventless fireplaces are not always permitted because they do keep the byproducts inside of your house. Ventless fireplaces are safest when installed in spaces that are themselves well-ventilated, like large rooms with lots of windows.