EL PASO, Texas -- As chilly days and nights hit the Borderland many are tuning on their heaters to keep warm.

"The man came and turned off the air conditioner's and lit the pilot so I think I'm going to be OK," said Betsy Seiler, who lives in Ruidoso.

Getting the heater on is one thing, but that's not all. Experts warn there are a few things you should do before you hit the switch. One of the first tasks is to check the filters to see if they need to be cleaned or changed, said Lee Zimmerman, a technician at Smith-Johnston Casa Plumbing. He said it’s also a good idea to peek at your burners to make sure they have good flames.

"I like to see how the flames look. You don't want to see any yellow in the flames,” Zimmerman told KFOX. “You don't want to see them rolling out. That's a sign of a problem."

And while some people are making a few checks, they sometimes forget another important step.

"I was actually doing the heater at my mom's house this morning,” said Greg Ayala, who lives in West El Paso. “She has two furnaces but I didn’t check the carbon monoxide. I don't have a tester."

Zimmerman said not testing for carbon monoxide is not the step to skip. Fumes could endanger someone’s life.

“Carbon monoxide is a colorless, odorless, tasteless gas. So you’re not going to know if there’s carbon monoxide being produced by your furnace," he said.

The average cost of a carbon monoxide tester is around $30. National numbers show that around 500 people die of carbon monoxide poisoning each year.