Check the wire gauge, not the package claims.

Look for 12 AWG (American Wire Gauge) or lower — and ignore marketing labels like “heavy duty” or “contractor grade.”

Space heaters pull 12 to 15 amps continuously. Most household extension cords are 16 AWG or thinner, which is fine for a lamp but can overheat under sustained load. That heat builds up inside the cord insulation and can melt it or start a fire.

What you actually want is a cord rated for the full current of the device and marked for continuous use. The simplest rule: 12 AWG for 15 amps, 14 AWG for 12 amps. If the cord doesn’t show the AWG number clearly on the jacket, don’t buy it. And never use a cord that feels warm to the touch after an hour.

A $15 cord is cheaper than a house fire.