Blower Door Test Common Air Leaks

Date Published: July 7, 2017

Understanding where to locate and seal blower door test common air leaks is important to ensure that a new construction home will meet the stringent requirements of the IECC and IRC code for maximum air leakage rates. Scott Home Inspection has performed hundreds of blower door tests on new residential homes, remodel-addition projects, and as a component of our energy audit services. We have a solid understanding of where the common leaks occur.

Before you start, it is important to understand what a blower door test is, and when you need a blower door test done on your project. Our blower door testing page will explain the process, and the IECC code requirements. The use of Infra-red scans can help determine the location and severity of leakage occurring.

Blower Door Test Common Air Leaks:

The top areas discovered in a home during blower door testing include:

Rim Joists:

In a conditioned basement or crawlspace, the rim joist area above the foundation wall can be one of the top leak areas. The typical foam gasket seal between the sill plate and the top of the foundation wall typically doesn’t provide enough of a seal to keep cold air from getting into the home.  As heat rises in a home and escapes through upper openings, cold air is pulled into the home from lower leakage areas.  The rim joist all around the perimeter is one of the most common lower level leakage paths we find.

Can Lights:

As the popularity of recessed can lighting continues in homes, these areas represent holes in the ‘thermal barrier’ of a home.  When properly installed, a gasket is used to seal the can light trim kit reducing leakage around the edges of the can.  Efforts to seal can lights to the drywall edge help reduce leakage considerably.

Attic Hatch:

When a hatch or scuttle to access the attic is located within the conditioned space of a home, then the edges of the hatch need to be sealed with weatherstripping and either a weighted, insulated hatch cover installed, or cam locks installed to keep the hatch in place and prevent leakage around the edges of the cover. The weather stripping we see most often is an adhesive style tape. This is one of the most common air leaks we see.

Window Sealing:

When windows are installed, foam sealant needs to be applied around the inside edges of windows to prevent leakage around the trim.  This is a common installation practice today, but on many older homes and energy audits we perform, leakage around windows can be a significant place where cold air can enter a home.  Removal of trim and sealing of window edges can help to avoid unwanted drafts.


New gas fireplaces often have side-wall vented flue piping and poor sealing around any outside wall penetrations can result in cold air entering around the fireplace and getting into the home, or providing a place for heat to escape. In older homes, poor sealing of the damper on older wood-burning fireplaces can be a significant source of heat loss in a home.

Door Weatherstripping:

Since the entry door on a home is opened and closed thousands of times, it stands to reason that the weatherstripping around the edges of the door can wear over time.  Ensuring that doors are sealing well with no gaps around the edges helps to prevent drafts and cold air from entering the home. This is extremely common air leaks

Furnace Ducts:

When heat ducts run through unconditioned spaces, such as crawlspaces, leaks around the joints and seams in the ducting can represent a large leakage area in a home.  Not only can this represent a pathway for cold air to enter a home, but when the furnace is running, heat can be pumped into the crawlspace versus to the desired register in the home.  The mice may like this, but it doesn’t make sense to heat or cool your crawlspace.  Seal all seams in the ducting to prevent heat loss and unwanted cold air entry.

Electrical Outlets:

In homes where insulation and air sealing wasn’t done well in the wall cavities, cold air can enter a home around the electrical outlets.  There are foam gaskets available that can be carefully placed behind the plastic outlet cover, to help seal the edges and prevent leaks.  We have seen this concern on new construction homes as well when penetrations to the outside are not sealed well prior to insulating. You can buy these gaskets in large packs like this one: L.H. Dottie WPI25 Wall Plate Insulation Gasket, 25-Pack

Whole House Fan:

Some homes have a whole house fan installed in the upper ceiling of the home, to pull warm air out of the house and help cool the home when the outside temps drop at night.  These units work great for that purpose, but in wintertime they can be a huge source of heat loss.  Covers are available that can either cover the unit on the inside, or if you can safely get to the unit within the attic, insulating covers are available to help reduce heat loss in winter (don’t forget to take it off in springtime!).  And when selecting a cover, look for air tight winterization covers, or self-closing insulated dampers.

Bath Fans:

The exhaust piping for a bathroom fan is a place where cold air can enter a home or heat can be lost.  Typically there is a damper that is mounted either at the fan itself, or at the exit point of the vent piping. However these dampers often don’t do an effective job of closing well and stopping air leaks.  If installing on new homes, ensure the quality of the fan purchased has a good damper system and that it is installed well.

Kitchen Hood:

At the exit point where the kitchen hood exhaust piping exits the home, leakage can occur around the edges when not sealed well, allowing heat to escape the home.  During installation, seal the perimeter of any exhaust piping for kitchen hood units.

Animal Entry Doors:

Although we all love our pets, dog and cat doors can be a massive leak spot during a blower door test. Consider removing the dog door, or sealing it as best as possible before the blower door test is performed.

These are some of the blower door test common air leaks we have noted during our testing of homes.  Whether you are performing a blower door test as part of the IECC prescriptive path requirements, or part of a HERS rating, or just for knowledge as part of an energy audit, work with a professional, experienced testing company.

Consider hiring Scott Home Inspection and our team of Energy Efficiency experts when you need a blower door test on your project.  We perform blower door testing for new construction IECC code requirements, or for existing homeowners as part of our energy audit services, helping to located blower door test common leak areas. We perform blower door testing in Denver, Boulder, Fort Collins, Castle Rock and all surrounding Colorado Front Range areas.  For more information visit the Energy-Service page of our website.  Also check out our related articles on blower door testing and IECC requirements at our Ask Your Inspector page.

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About the Author: George Scott

George founded Scott Home Inspection in 2006, and has grown the business into a multi-inspector firm serving the Colorado Front Range, from Fort Collins down to Colorado Springs. As an ASHI Certified Home Inspector and Certified Energy Rater, George is an excellent resource to help with inspection and energy-related requirements.

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