The DOE estimates that 20-40% of the money an average American family spends on heating and cooling their home each year is wasted through uncontrolled air leakage, insufficient insulation and failing duct work. It's no surprise then that air sealing is almost always a top priority. Air sealing is done with a two component closed-cell spray foam, (it is important that a close-cell foam is used to ensure proper sealing).
Gaps and cracks around attic penetrations (plumbing, electrical, chimneys etc.) are sealed with this foam. Top plates (where the interior walls connect to the attic and basement rim joists (where the foundation connects to the floor of the house) are also major areas or air leakage and often need to be sealed. Weather-stripping around doors and windows are sealing wall outlets are also effective in reducing air leakage.
In addition to air sealing, proper levels of insulation are needed. It might surprise you to know that most homes in the United States are under-insulated based on current DOE standards. How many inches of insulation do you have in your attic? What is the effective R value (thermal resistance) of that insulation? A certified building energy analyst can help you determine if more insulation is needed.
According to ENERGY STAR, about 20 percent of the air that moves through your duct system is lost due to leaks and poorly sealed connections. While some ducts may not be accessible since they are behind walls or in floors, all exposed ducts in a non-conditioned space may be improved by using a duct sealant. Mastic is the type of sealant preferred instead of the foil tape that is often seen on duct connections.
You may be wondering if a house can be too tight. We certainly need fresh air in our homes. Using a blower door to test the leakiness of the house while performing air sealing can ensure that proper ventilation is present in the home. A better solution, however, may be the introduction of mechanical ventilation.
Mechanical ventilation, as opposed to random air leaks in the house, ensures the right amount of air exchange year-round under all conditions. Mechanical ventilation can also be used to control the quality of air passing through the home for better health. The basic rule of thumb in building science is 'seal tight; ventilate right.'
In addition to improvements to the building shell, attention should also be given to improving the efficiency of your heating and cooling system. How old is your furnace, boiler and air conditioning system? What was its rated efficiency when it was installed? What do you think its efficiency is now?
For furnaces, consider a sealed combustion, variable blower system with an Annual Fuel Utilization Efficiency (AFUE) of at least 95 percent for greater safety and higher efficiency. If you live in a hot climate and have an older air conditioning system, chances are good that replacing your system with a new, energy efficient model will pay for itself in energy savings. The most efficient units on the market have Seasonal Energy Efficient Ratings (SEER) of 18 or more. You may also want to consider a heat pump or a geothermal heat pump depending on the climate and utility/fuel rates where you live.