Easy Answer: The techie things.
A professional energy audit will probably run a few hundred bucks, though some utility companies offer discounts and others will audit your home for free (it's worth checking). I met up with energy auditor Dan Thomsen, who owns a company called The Building Doctors, to find out what a professional energy audit includes that our DIY audit doesn't.
One of the things an energy auditor will do is a blower door test. The auditor will install a temporary door with a high-power fan in your door frame.
The test can help determine how airtight your home really is by pressurizing and depressurizing your home. For more on how blower door tests work--check out this explanation from the DOE.
An auditor will also use an infrared camera to help spot temperature differences in your home's "skin" so he can see where your house is well insulated and where it isn't.
The images can help an auditor figure out if you need additional insulation and if the insulation you have has been properly installed. More here.
If you do decide to go with a pro be sure to check their credentials. Consumer Reports has advice about what to look for in an auditor, and what to avoid.
PHOTO: Adriene Hill
"Also remember that not everyone who hangs a green shingle has the training to identify inefficiencies. There are eco-consultants, who might charge $99 for a 60-minute walk-through of your home, pointing out leaky faucets and inefficient lightbulbs. Then there are general contractors who see energy efficiency as the one bright spot in an otherwise shrinking industry. Last but not least are single-product salespeople. "Homeowners have been hearing forever that replacing their windows can save 40 percent," says Chandler von Schrader, head of the Environmental Protection Agency's Home Performance with Energy Star program. "These claims aren't justified and they create a false expectation.""