5 Things to Know About Extension Cords for Block Heaters

Use a cold-weather rated cord Normal extension cords turn brittle and crack at -30°C. Look for a cord rated SJTW or SJOW, which stays flexible and resists cracking in extreme cold.

Choose 12-gauge for runs up to 50 feet A block heater pulls 1000–1500 watts. 12-gauge copper wire handles that load safely. 14-gauge might work for a short 15-foot run in a garage, but 12-gauge is the safer bet outdoors in extreme cold.

Undersized cords risk fire A cheap, undersized cord can melt its insulation under a block heater’s load. The extra cost for 12-gauge buys voltage headroom and reduces fire risk.

Ensure sealed connections Snow and slush get into loose cord ends. Look for cords with molded plugs or protective boots to keep connections dry and tight.

The investment is worth it A proper cord costs about ten dollars more than a basic one. Your truck starting in the morning is worth that difference.