Many of us have laptops for work or school. Perhaps they are so widespread because of their convenience; laptops have all the power of a desktop computer, but the portability of a paperback.

However, owning a laptop may have unexpected risks. Leaving one unattended on a bed or sofa could cause a house fire.

One Virginia family learned this lesson the hard way, when part of their two story condo was burned to the frame, causing about $40,000 worth of damage. The cause appears to be a laptop that was left running in an upstairs bedroom on a bed. "It was running for sixteen to eighteen hours," says Frank Teevan, a fire marshal in Virginia.

The offending computer was a Hewlett Packard HP Pavilion that was running on a recalled battery. The Consumer Safety Commission says that between 2005 and 2010, multiple manufacturers recalled a million laptop batteries. "Unfortunately in this case, the owner didn't know that she had a recalled battery. She put it on her bed on top of a comforter on her mattress the night before she fell asleep. She left that morning to go to work and left the laptop running, plugged in on her bed," said Frank Teevan, a fire marshal in Virginia.

However, the recalled battery wasn't the only issue. Laptops left on soft bedding or furniture are always a potential hazard. Computer technicians warn that the air intakes that keep a laptop cool are located on the bottom or side. Leaving a one on a soft surface can block these vents, allowing it to overheat. Laptops are meant to be used on a hard surface so air can move through the vents and cool the machine. Otherwise, you might end up with a laptop like the family in Virginia's. "It got so hot it ignited the blankets and the comforter on the bed and just went from there," Teevan said.

Warning Signs

You can protect your home from fires by keeping an eye out for these signs that your laptop is overheating.

If your fan is constantly running or making loud whirring noises, you may have a problem. The fan is what draws in air to keep the laptop cool, and if it's malfunctioning it's not doing its job.

If your vents are clogged, try using compressed air to blow out the dust, or take it to a computer repair shop to have them cleaned. Another sign of overheating is slow speed. If your computer has trouble with simple tasks, such as opening a browser window, or mysterious error messages pop up, it could be due to excessive heat. If the laptop suddenly freezes or shuts down on its own, it could be a sign of hardware failures, also caused by overheating.

However, its always a good idea to keep your laptop on a hard surface, where it has the best opportunity to cool properly. "I wouldn't leave any electronic device on any type of combustible material for any length of time," says Teevan.