Testing for leaksBefore considering insulation improvements, first find and plug air leaks—holes, cracks, and gaps that let cold air in and warm air out in the winter—and do the reverse in the summer. If you feel drafts in the winter, that’s an obvious sign of leaks. If you consistently feel chilled between furnace cycles, that’s another sign.

One little leak might not seem like much, but the cumulative effect of several leaks can amount to the equivalent of leaving open a small window. If you have a lot of leaks, they will dramatically decrease the value of any insulation you add.

You can track down major air leaks on your own by taking the following steps: (1) Turn off your furnace on a cool, very windy day; (2) Shut all windows and doors; (3) Turn on all exhaust fans that blow air outside, such as bathroom fans or stove vents; (4) Light an incense stick and move around your house; where smoke is blown, there’s a draft. Focus on inspecting areas where different materials meet—brick and wood siding, foundation and walls, and between the chimney and siding. Other common problem areas—

  • Door and window frames
  • Mail slots
  • Points of entry for electrical and gas lines, cable/satellite TV wiring, and phone lines
  • Outdoor water faucets
  • Where vents pass through walls
  • Cracks or gaps in siding, stucco, masonry, all foundation materials
  • Around window air-conditioning units

Use caulk to seal any cracks or gaps measuring less than 1/4 inch wide. For larger cracks, use polyurethane foam sealant. To minimize leakage around doors and windows, install weatherstripping. Open-cell foams are inexpensive and relatively inefficient but easy to apply and suitable for low-traffic areas. Vinyl is more expensive and lasts longer. Metals last for years and provide a decorative element for older homes. Choose according to location, function, and appearance.

Finally, check for holes or gaps in exposed ductwork and seal them with duct tape. Leaky ducts can waste 20 percent or more of your home heating energy bill.

A good energy auditor can identify even more leaks using equipment that will find leaks you can’t find yourself. Before shelling out $300 to $500 or more for a full audit, find out if your utility company offers basic energy audits for free or for a heavily discounted ($99 or so) fee.

Also, before paying for a full audit, confirm that the contractor will use a calibrated blower door to measure the overall air leakage of your home, and make sure it will perform a thermographic inspection using an infrared camera, and if you’re paying for the audit, hire one certified by the nonprofit Residential Energy Services Network (Resnet). Certified auditors must complete Resnet’s training program and carry a minimum of $500,000 in liability insurance.