No, it is not safe to leave a propane heater on overnight. Even if you’re using the heater in a well-ventilated space, the heaters can emit carbon monoxide that can lead to fires. Be sure to fully turn off and secure the propane heater before clearing the area. 

Yes, you should seal and cap an unused chimney to protect it from damage. Sealing the structure helps prevent moisture damage, which can lead to issues like cracks, spalling, efflorescence, and damaged mortar joints. Capping the chimney is also crucial to prevent blockages, damage from invasive critters, and downdrafts, while still allowing for proper air ventilation to manage moisture. For the best results, consult a chimney professional to select the right type of chimney or flue cap for your home. It's also wise to continue with annual chimney inspections to maintain the structure's integrity.

If a light switch is off, it’s very unlikely to cause a fire. For a fire to start, the switch has to be on, activating an electrical current, and the wiring must be faulty. However, the malfunctioning light switch could cause an intermittent current to move across the electrical wire. This issue could become a fire hazard with another device connected to the wire. You should replace the bad light switch as soon as you notice it or call an electrician.

Your pilot light needs to be on whenever you’re using your furnace to heat your home. However, you might decide to turn it off during the summer months, when you don’t need heating. Doing this can save you a little bit of money on utility costs—just make sure you’re fine with relighting your pilot light (or hiring a professional to do it) when fall comes around and you’re ready to get cozy.