As it gets colder across the northern hemisphere, many people use space heaters to stay warm. However, firefighters warn that you need to be very careful with how you use them—especially when it comes to how you plug them in. The Umatilla County Fire District in Oregon says you should never plug a space heater into a power strip. Power strips aren’t built to handle the high electrical load space heaters require, and they can overheat or even catch fire.

This is a real danger. In one case in Ohio, a space heater plugged into a power strip caused a couch to ignite, and the flames quickly spread, destroying the entire home. Space heaters can reach temperatures as high as 600 degrees Fahrenheit, making them a serious fire hazard if not used properly. Because of these risks, safety experts stress the importance of using them with caution and care.

To reduce the risk of fire, firefighters recommend several important safety steps. Always plug your space heater directly into a wall outlet—never into a power strip or extension cord. Keep at least three feet of space around the heater, clear of furniture, curtains, bedding, or anything flammable. Only use space heaters when you’re in the room, and never leave them on while sleeping or away from home. Always place them on a flat, stable surface, never on furniture or rugs.