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Space heaters account for only two percent of all house fires, but they cause 45 percent of all fatal heating fires – killing dozens of people in the U.S. each year.

Because of that, FOX31 Denver tested some popular space heaters with help from some local firefighters, to see how dangerous they could be.

We tested a Sunbeam model, a Comfort Zone brand heater, and an Optimus heater – all relatively close in price and available at many big box retailers.

Using a thermal imager, we turned on each heater, and then read the surface temperature of each one.

The first model we tested, the Sunbeam, reached temperatures between 375 and 450 degrees within a minute of turning it on.

The second heater, a Comfort Zone model, shot up to between 200 and 300 degrees in just 45 seconds.

The Optimus heater was relatively cooler, but still dangerous, taking about one minute and 50 seconds to reach its maximum temperature – hovering close to 200 degrees.

“Anything over 75 degrees will burn you,” said Lt. Kinny Tasker, a firefighter with South Metro Fire Rescue. “You could get third degree burns from that.”

Aside from scalding temperatures, these heaters can be deadly if placed too close to household items.

“People go to sleep with them running, or they go to sleep with them too close to bedding,” said Becky O’Guin, a spokesperson for South Metro Fire.

O’Guin says part of the reason space heaters can be so deadly is because they often don’t ignite flames – but smolder, silently filling our homes with toxic chemicals.

“People die from smoke inhalation before they die from the fire itself,” said O’Guin.

To test how quickly these heaters create smoke, and how long it takes before each heater’s automatic safety shot off switch works, we placed each next to a pillow.

The first heater, the Sunbeam, began smoldering in just two minutes. It took four minutes for the heater to burn through the pillow and fill the room with smoke.

It took more than six minutes for the heater to finally shut off – though the pillow continued smoldering.

The Comfort Zone heater, the second model we tested, began smoldering even quicker – within a minute, toxic fumes began filling the room.

It continued running for more than five minutes – before shutting off, as the pillow continued smoldering.

Finally, the third heater we tested, the Optimus model, took just over a minute to smolder. It then took almost 10 minutes to finally shut off during our experiment.

Becky O’Guin says that while these kinds of fires claim innocent lives every year – they can easily be prevented – with common sense.

“Never leave the room with a space heater running and always make sure you turn it off before you leave the room or go to bed at night,” O’Guin suggests.

“Also, keep space heaters at least three feet away from anything that can combust or catch fire.”

Lastly, O’Guin says keeping working smoke alarms inside your home is the best line of defense in case of a fire.