Why Air Sealing is Crucial to HVAC Efficiency

All the major utilities in Arizona are offering rebates for sealing air leaks. Air leaks are unintentional openings in your home that let conditioned air escape. Conditioned air is the air that you pay to heat and cool to keep you comfortable. The more conditioned air that unintentionally escapes from your home, the more likely you’ll be uncomfortable and have higher utility bills. In this section, our goal is to provide a very basic overview of air leakage, infiltration, indoor air quality and air sealing process for our customers.

AIR SEALING & AIR BARRIERS

Air infiltration, building airtightness, indoor air quality and air sealing provides unique challenges for us at Advantage Home Performance. We recognize that if a house has excessive air leakage the house will be uncomfortable and expensive to heat and cool. The other extreme is a house that is too tight and does not have any provision for fresh air ventilation, will be more susceptible to indoor air quality issues. Our goal, given our customers budget and the realities of a building, is to find the level of building airtightness in which we get the optimal level of comfort, efficiency and indoor air quality. We cannot accomplish this goal without the use of diagnostic testing.

We use a blower door to measure a home’s level of airtightness. We can determine fairly quickly if a house is leaky, tight or about right given the size of the house and the number of occupants living in it. The blower door also permits us to calculate the approximate size of the hole that would be created if all the unintentional holes were combined. We use this information to help us determine what solutions would make the house more comfortable, energy efficient, healthy and safe.

Another benefit of using a blower door is that it can lead us to the unintentional holes or air leakage sites. Most homeowners are under the false impression that air leaks around windows and doors.

Most homes are full of hidden holes that let conditioned air escape. These same leaks can negatively impact the performance of the insulation. In Arizona, leaks in your attic from plumbing penetrations, electric wires, light fixtures, and building chases that are not capped off represent significant energy losses. Sealing these air leaks is a critical step to improving the overall efficiency and comfort of your home.

SMALL AIR LEAKS

Air sealing work typically consists of sealing up small leak sites with foam. In the photo below you can see where the crew pulled back insulation from top plates and used a can of spray foam to seal the cracks.
Our crews seal all plumbing and electrical wiring penetrations. These are the types of leaks that we routinely see as part of air sealing work. In the photo on the left you can see what should happen when this house was constructed. A can of foam with a gun can quickly seal all these small air leaks. Unfortunately these plumbing pipes and electrical penetrations are rarely sealed.

Air sealing with foam gun	Plumbing penetration in top plate: attic view

LARGER AIR LEAKS

We often deal with larger leak sites where there are no top plates or draft stopping at ceiling height changes. In the two photos below the framer never put in blocking which is called draft stopping. This is a code requirement to prevent the spread of fire, but it also creates convection loops in which warm air in the winter rises up the interior wall cavity and into the attic.

The solution to these types of problems is straight forward. Our crews cut duct board and insert into the hole with a friction fit. Then they glue air barrier material into place with foam insulation. We refer to this type of work as air barrier work. Once we are done we can blow insulation over the air barrier material.

Missing draft stop	Air barrier work

RECESSED LIGHT FIXTURES (CANS)

Another example of an air leakage site that is easy to visualize are older recessed light fixtures. These recessed light fixtures can be very leaky. To highlight the problem, I selected two slides taken in attics showing light pouring out of the recessed cans. In the picture on the right when the attic is dark you can see how leaky this recessed light fixture is because light is streaming out of it. Some of these older recessed light fixtures leak like colanders.

Attic view of recessed light fixture	Light streaming out of recessed can in attic

The older recessed light fixtures we see in homes often require the insulation to be kept clear of the fixture by 3”. The problem with recessed light fixtures that require clearance is that they create insulation voids that undermine R-value and as you have seen in the photographs above they are also very leaky.

Recessed light that requires 3” insulation clearance	Air barrier & insulation box for recessed light

Our solution is to entirely air seal and isolate the recessed light fixtures. The boxes we fabricate are constructed out of duct board. The duct board provides both an air barrier and R-value. We don’t have to keep insulation clear of the box we made because the box is insulated and creates the required clearance.

OPEN CHASES

Large chases as seen in the photos below with batts laid over them are unacceptable as well. The fiberglass batts are air permeable, air will migrate through via air infiltration and stack effect. Stack effect occurs in the winter when warm air naturally rises like a hot air balloon. These open chases are easily capped with plywood, OSB or duct board. It is not difficult to address these issues.

Large duct work chase in Phoenix home	Large open chase behind fiberglass tub enclosure

DUCT LEAKS

The most problematic air leaks in a home are the ones in the air distribution system. Duct leaks have a big impact on utility bills and indoor air quality.   The leaks garner a lot of attention because when the air handler fan is running these leaks see the highest pressures. In the photo below on the left side you can see a big return leak which is sucking hot dusty air right out of the attic. In the picture on the right hand side we see a disconnected supply duct which means this customer is cooling their attic. This is why the utilities have special rebates for sealing ductwork. We dedicate a special section of this website to duct leakage.

Large return duct leak in Phoenix home	Disconnected supply duct in attic

BUILDING AIRTIGHTNESS & INDOOR AIR QUALITY

We adopt three strategies when performing air sealing work in our customer’s homes to help ensure that we don’t compromise indoor air quality. The first is to address potential indoor air quality problems beginning any work. For instance, if a customer is burning scented candles or has a damp crawl space we would not do air sealing work until the customer agreed to get rid of the scented candles and the moisture issue was resolved.

The American Lung Association’s Health House project recommends that a house should be “built tight and ventilated right.”  When we have customers who appreciate that we heat homes mechanically, cool them mechanically and ought to be ventilating them mechanically we approach the house differently. If we are going to install a fresh air ventilation system in a house then we seal the house as tight as we can.

If we know ahead of a job that the customer is not interested in investing in a fresh air ventilation system, our crew stops air sealing when we reach an airtightness target called the minimum ventilation rate (MVR). The MVR lets the crew know they have reached the airtightness goal for the specific house. By air sealing past the MVR, we run the risk of solving one problem for our customer and in process potentially create another.

SUMMARY

It makes no sense to spend money to condition air only to have it immediately escape. The air barrier rebate for air sealing is a great value. Over the years we’ve seen a lot of attics that have been reinsulated without any concern for the air barrier. At Advantage Home Performance we think no energy conservation work should begin without an audit.

The key to improving the efficiency and indoor air quality of your home is having a competent auditor who will strike the right balance between building airtightness and indoor air quality come out to your home to perform an audit.