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Weatherization 101 and What to Expect From Your Energy Assessment

October-November 2012

Community Energy Challenge

Weatherization 101 and What to Expect From Your Energy Assessment

The energy assessment is an unparalleled opportunity to get to know your home in a way that even living within its walls for many years may not afford you. You know where the cold spots and drafts are, which rooms get a little mold around the baseboards in winter, and which heater vent never warms up as much as the others, but an energy audit by a Building Performance Institute certified analyst can uncover and quantify all of the interrelated effects of your home’s construction and the condition of your appliances on your comfort and energy bills. You may know that your home is leaky and needs air sealing, but having a blower door test and learning exactly how much sealing will make your home more comfortable without sacrificing air quality will make your home improvements more focused, successful, and cost-effective. Not only will weatherization make your home more comfortable and energy efficient, but many of the measures will also contribute to your home’s value, durability, and safety. Here is a look at some common weatherization techniques and how a home energy assessment can help you choose which measures are right for you.

The Energy Assessment

The energy assessment gives a big-picture look at the energy efficiency condition of the house and can alert the analyst to any pressing health and safety concerns. It helps establish cost-effective priorities for improvements and lays out an order of operations for work to be done effectively, while locating and identifying problem areas in the home.

During the assessment, the analyst evaluates the home’s building shell and inspects energy-using appliances. A variety of specialized diagnostic equipment is used to learn more about the condition of the home. The building performance analyst uses a blower door and a manometer to determine locations and measure the amount of air leakage in the building shell and ductwork. An infrared camera can also help to point out gaps in insulation and to further reveal air leaks. If there are gas appliances, the analyst will perform combustion safety testing. Combustion safety testing helps prevent occupant exposure to carbon monoxide and other harmful gases by making sure that all heating and cooking equipment are operating safely.

Air Sealing

In a typical leaky attic, upward pressure from the stack effect—the tendency of warm air to rise—can replace all of a home’s heated inside air with cold outside air in just two or three hours. Air leaks tend to occur at connections between different building assemblies and joints between components, at electrical, plumbing and mechanical penetrations, and around windows and doors. Measuring air loss with the blower door and then sealing the air leaks to the most efficient level keeps the air you are paying to heat within your home and keeps “dirty” air from your crawlspace from flowing into your home in the place of fresh air. Air sealing also helps reduce drafts and cold air from entering the home and helps assure that insulation will function at its rated effectiveness.

Duct Sealing

Heating system ductwork can leak heated air at duct seams and connections, and duct tape tends to lose its grip over time, so the analyst will look for opportunities to repair any leaky ducts. With improperly sealed ductwork, anywhere from 20% to 40% of the air that comes out of furnaces never gets to the rooms it’s supposed to heat. Not only does duct sealing help deliver heated air where it’s intended to go instead of dumping it outside, it helps exclude air pollutants that would enter the duct system from crawl and attic spaces and corrects imbalances in air pressures throughout the house. Pressure balancing is important for the durability of the house and for the safe operation of combustion appliances.


Having a continuously insulated building envelope is the best way to keep your home warm in the winter and cool in the summer, and since hot air rises, attic insulation is usually identified as the first priority when making insulation improvements. If the coverage of your existing insulation is incomplete, the effective R-value (resistance to letting heat escape) drops by a factor far greater than the area of reduced coverage. For instance, if gaps in your attic insulation account for 2 percent of the area, the effective R-value drops by 42 percent.

Uninsulated exterior walls can be insulated by blowing a high density of cellulose into holes drilled through inside or outside wall surfaces. This process is minimally invasive and the holes are filled afterwards and are very easy to patch and conceal. Cellulose in walls is considered a very effective insulator because it doesn’t allow airflow to the extent that fiberglass batts do, and with proper installation it leaves very few voids. This “dense pack” insulation can also serve as a type of air seal because the fibers build up and fill tiny gaps in the inner surfaces of the cavity.

In order for under-floor insulation to be effective, it must be adequately supported so there is no gap between the floor and insulation. During the energy assessment, the building analyst will enter the crawlspace to make sure the floor insulation is forming a continuous barrier and will assess the condition of insulation on the ductwork as well. If there is an opportunity for improvement, they will recommend insulating the ductwork and water pipes that run under the house.

Ventilation and Indoor Air Quality

Controlling moisture, mold and air quality in the home is another primary goal of weatherization. Measuring air leakage and then air sealing and insulating to the proper levels can help assure that fresh air comes into the home through intended ventilation pathways and isn’t traveling through crawlspaces and walls before you breathe it. A building analyst will also make sure the home has enough mechanical ventilation (such as bathroom fans and a range hood) as needed and that the pressure balance in the home is allowing combustion appliances to work safely. The analyst will also assess the condition of the moisture barrier in the crawlspace under the home. An uncovered or poorly covered dirt floor presents a constant supply of water vapor into the house and causes air quality and structural durability problems. Installing a strong layer of polyethylene sheeting that thoroughly covers the crawlspace floor improves indoor air quality by limiting mold growth and containing soil gases, and improves building durability by keeping moisture out.

Heating, Ventilation and Air Conditioning

The building analyst will assess whether aging heating equipment presents the opportunity for an efficient replacement. Two of the best options on the market right now are heat pumps and high efficiency gas furnaces. Ductless Mini-Split heat pumps are an electric heat source that use heat-pump technology to heat the home (and cool the home in the summer months) but do not require ducting, so installation is relatively simple. Heat pumps concentrate heat found in the ambient environment and move it to the interior of the home. They make very little noise and are over 100 percent efficient as a heat source! If a gas furnace replacement is needed, the CEC energy advisor will recommend the highest efficiency rated furnace that is practical for the homeowner’s budget. High efficiency furnaces are also known as direct vent, closed-combustion furnaces and are much safer in terms of combustion safety, and are commonly more than 90 percent efficient.

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