Hager Fox furnace technician Jeremy Agler is in the business of keeping you warm.

"I look to make sure your furnace is operating properly, make sure it's safe," Agler says. "Try to cut down on utility bills if we can."

We're heading into the busy season for furnace upkeepl as the temps drop, you want to make sure your heater is working properly. But where there's opportunity, there's often people knocking-- literally-- on your door.

That's exactly what DELEG is warning against. The state department says at first it may seem convenient when someone calls you or comes to your door to clean your furnace. But where it makes up in convenience, it may lack in legitimacy.

DELEG reports people have been scammed out of as much as $30,000 by cons who say they're cleaning your furnace, then hit you up for other repairs they say are necessary.

The state is offering a few tips to make sure you don't get fooled.

Do ask to see the contractor's license, do make sure the license is valid and do get three independent estimates before doing business.

"Those are reasonable requests," says Agler, who's been in the business 11 years. "There's nothing wrong with having a little knowledge on what you're buying."

Here are some don't's:

Don't fall for telephone solicitations, don't be pressured into a signing a contract and don't hire someone who comes to your door.

"I wouldn't do any business with someone who calls and says 'I can get you a heck of a deal,' because it probably won't be? It probably won't be," Agler says.