For a more detailed approach, get a professional energy audit. You can find a list of auditors in Minnesota on the Minnesota Building Performance Association website. Don't be afraid to shop around for an audit; you want to make sure you're getting what you pay for.

Professional audits should consist of a blower door test, to determine air-tightness of your home, and a thermographic scan is useful to see thermal defects and points of air leakage.  A blower door test will quantify how much air is leaking from you home, and a thermographic or infrared scan allows you to identify which areas are responsible for the leaks. This will show you cold spots around openings, thermal bridging, and areas lacking insulation. Find professional auditors and learn more about audits and home performance. In addition, check with your local utility company for what assistance they may have for professional energy audits.

How does a blower door test work?
During a blower door test, a fan is used to depressurized your home to -50 pascals with respect to the outdoors.  A computer attached to the fan calculates the airflow in cubic feet per minute (CFM) to determine the leakiness of your home. The resulting value can be translated into an area of measurement called the approximate leakage area. While lower leakage means a more energy efficient and comfortable home, ventilation is important to keep the inside of a home dry and free of pollutants and to avoid dangerous carbon monoxide back-drafting from gas appliances.  The minimum CFM values needed in a home depend on the number of people in your home and type of combustion appliances, and if the leakage drops below that number add mechanical ventilation.  See this chart [go to page 98: Table 5.2 in the Minnesota Weatherization Field Guide] to find that number for your home.

The audit should also include an assessment of your combustion appliances and visual inspection of the roof, attic, walls, basement, and foundation for moisture, structural, or any other issues that may be present.  Ask the auditor for help writing a work scope for improving the efficiency and comfort of your home.