Vehicle block heaters are working overtime this week as cold temperatures have returned to the southeast.

If you're wondering how long you should plug your vehicle in before using it, Bill Fonstad, owner of the CARSTAR autobody shop in Estevan, has the answer.

"Of course depending on how cold it is, but I would say for me it's a minimum of two hours," Fonstad said. "But I mean if you're in a hurry and you've only got an hour, plug it in. It's better than nothing."

Fonstad said having your vehicle plugged in for multiple hours or even days won't do any harm to it, but it comes at a cost.

"It doesn't hurt your car to leave it plugged in, but you're using electricity that you don't need," he said. "If you plug it in two hours before you're going to start it, or four hours, or if you have it set on a timer that's even better."

Fonstad said he usually starts his vehicle before unplugging it, though this doesn't really matter one way or another, just as long as you don't forget to unplug before driving away.

He also explained how a block heater operates underneath the hood.

"A block heater warms up the block of your car, which is the main part of your engine," he said. "And what that does is it warms up your anti-freeze that's in the block which warms up your engine, and it also warms up your oil a little bit."

He added that it's imperative to plug in when it gets colder than about minus 18 degrees Celsius.

"There's nothing worse for an engine than a cold start," he said. "So you're doing yourself a favour and your car a favour."