Q: We are ready to increase the insulation in our older home, but we have been told that we need to air seal first. What do they mean and what is involved?

A: Before we add insulation to our attics or floors, we need to air seal our homes. Most homes can loose 20% to 50% of their heat through air movement passing through openings and holes in the envelope of our heated living space.

New homes, and ones built by conscientious builders in the last few years, address most of these issues. However, since most of our housing stock is over five years old, there are many areas that can be addressed and improved. Typically, the older the home the higher the return and the faster it pays for itself.

Common openings that need to be sealed:

  • oversized holes at the plumbing pipes and electrical fixtures.
  • the heat register transition to the floor
  • ducting with gaps open to the crawlspace
  • usually electrical outlets, wall switches, and ceiling fixtures (with attics above) are poorly sealed
  • poorly fitting fireplace dampers, gaps at the wall and brick fireplaces as well as the gas pipe penetration below manufactured fireplaces will let a lot of air into or out of the house.

We typically have negative air pressure in our homes. Unbalanced heating systems, dryers and exhaust fans all pull air out of our heated space. Additional heat loss through ill fitting attic access panels, older versions of recessed lighting fixtures, and poorly sealed exhaust fan penetrations, allow the warm air to escape through finished ceilings. This causes a vacuum that pulls cold air in through our plumbing pipe openings, floor register gaps and wall outlet openings. This results in hot air rising, which pulls colder air in. This is called the Stack Effect.

A cubic foot is roughly the volume of a basketball, so when a dryer can draw 200 cubic feet per minute (cfm), picture 200 basketballs worth of air leaving your house every minute. A good reason to open the laundry window a crack in order to prevent a vacuum drawing cold air from your crawlspace and attic, into the house and clean clothes.

So back to air sealing, prior to adding insulation, it is very wise to have someone seal all the various openings from the crawlspace and attic into your house. Think about the quality of air from these places, it’s not very good! All the more reason to seal them up. The exterior walls need attention too with doors, windows, chimneys, and fans providing air intrusion points.

Many of the gaps and openings are very accessible before we add insulation and are therefore less expensive to locate and block. Often there is very little one can do to better the attic if its already filled to the gills with insulation, limiting access and room to move.

DO IT YOURSELF TRICK for finding air leeks:

Close all of the windows and doors in the house and turn on all of the exhaust fans; kitchen, bathroom, and laundry fans as well as the dryer. Then start walking around the house checking the exterior walls, top floor ceilings, and bottom level flooring. Use some incense near the drywall penetrations, seams of dissimilar materials, windows, doors, and fixtures to see where the smoke indicates airflow. Professionals use blue painters tape and seal them as they go. This helps identify the places for corrections and increases the tightness of the house, making it easier to find the smaller openings. This is a great tool, unless your older home has too much air leakage to create negative air pressure to begin with.


After you have tried this you may find that having a professional crew come in and do a blower door test makes sense. They use a strong fan to depressurize the house and locate the openings. Your money is much better spent if you have the same people doing the testing and also sealing things up as they go. Someone coming in to test and write you a report, followed later by a separate crew to seal things up, leaves much to be desired. They may not be able to locate all of the places or know if they sealed them well as they go.

Another tool that trained crews use is duct blasters. They pressurize our heating ducts to test and locate leaks in seams and fittings. Most homes with furnace ducting in their attics and crawlspaces are heating these uninhabited areas. Although the mice appreciate the expense, the result is a tremendous amount of heat loss from poorly installed and sealed furnace systems. If your furnace is located outside of the heated envelope of the house, chances are very good that there are gaps at the seams as well as uninsulated ducts heating your garages. This is not only a heat loss area but makes your heating system very inefficient due to different pressures inside and outside of the home. If our furnace is trying to force air into the house while loosing air into the attic and crawlspace, it ends up sucking air in from outside of the house to balance the demand of your return air system.


Another advantage of hiring a professional crew is that they should be trained to prevent  indoor air quality problems due to potential back drafting furnaces and water heaters. One of the worst situations is a gas water heater located in the laundry room. Back to the 200 cfm of air needed to dry the clothes– if the room can’t provide enough air it will pull exhaust fumes into the house from the water heater or furnaces. Remember to install those carbon monoxide detectors.


Although air sealing and insulation don’t initially seem to improve the appearance of our homes, we get a far larger return on our investment than we would buying those new windows that every magazine, newspaper and TV add tell us we need. As a result, our money can go a lot further. Start out with air sealing, move on to upgrading your insulation and then consider buying those new windows. You will be more comfortable and save far more money on your heating bills.

Now is a great time to act with the tax credits available. We can save energy, make our homes more comfortable, save money and lower our carbon foot print all at the same time. Most of these improvements pay for themselves in 3 to 5 years.

Things to remember:

  • always air seal prior to adding insulation
  • blower door testing is the best method to locate leak
  • we can save money, make our homes more comfortable and decrease our carbon foot print at the same time
  • a blower door test, with workers sealing things up as the go, is the most effective and less expensive than a separate test and report
  • care needs to be taken to prevent creating indoor air quality problems
  • tax credits are available to offset the costs