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How to Air Seal Your Home

Although seemingly insignificant, the tiny cracks, holes and gaps that develop in your home's "envelope" – its exterior walls, ceilings, floors, windows and doors – can cause serious damage to your wallet, home comfort levels and health. Air leaks like these can both introduce unconditioned air into your house, and allow heated or cooled air from your home's interior to escape. Ultimately, this will reduce your home's overall energy efficiency, create uneven temperatures, and degrade indoor air quality. Because of this, it's a good idea to learn how to air seal your home effectively. By following this guide, you will discover how to detect energy-wasting air leaks, as well as how to properly seal them to promote energy savings and enhanced comfort.

How to Locate Air Leaks in Your Home

Before worrying about learning how to air seal your home, you must be able to pinpoint the problem areas. In some instances, air leaks may be quite obvious. For instance, drafts that enter your home under doorways or around windows can easily be felt by household occupants, but you'll need to dig a bit deeper in order to find the less noticeable leaks that may have have developed in your home. The most thorough way to accomplish this task is by enlisting the help of a technician who is qualified to conduct a home energy assessment, in particular, a blower door test. Using a frame containing a high-powered fan that's inset into a main door of your home, this type of comprehensive testing will depressurize your home, and then use gauges to calculate how quickly the outside air rushes back inside and equalizes the pressure. If the pressure equalizes quickly, this means your home isn't very airtight. This test also may use thermographic scanning to detect where the air is leaking, as well as identify areas where insulation is lacking.

In lieu of calling your HVAC professional, though, there are a few do-it-yourself ways of finding air leaks. Here are two relatively simple ways to go about detecting these problem spots:

  • Visual inspection – Take a few moments to walk around the outdoor perimeter of your house, and thoroughly inspect any areas where two different types of building materials intersect. These areas could include outdoor water faucets, places where siding and chimneys come together, spots where the foundation and the bottom of exterior brick and/or siding touch, and all exterior corners. Once you have noted any obvious cracks or holes outside, you can take your inspection inside your house. Here, you should look for gaps around electrical outlets, switch plates, utility or plumbing service entrances, baseboards, windows and doorways, window or wall-mounted air conditioners, attic hatches, fireplace dampers, and places where dryer vents pass through your walls. Even if you have previously applied caulk or weatherstripping to these areas, check the seals to make sure they're properly in place, fully intact, and not allowing air to leak in or out of your house.
  • Building pressurization test – Another option is to conduct a simple building pressurization test, basically a scaled-down blower door test. This process will increase infiltration through any cracks or holes, making them easier to detect. To do this, you will need to turn off all of your household combustion appliances, including gas furnaces and water heaters, on a cool, windy day. Next, shut all windows, exterior doors and fireplace flues, and turn off any exhaust fans that blow air outdoors (i.e.n bathroom fans, kitchen hoods, dryer vents). Then light an incense or smoke stick and walk around the inside of the outer walls of your house, moving the stick close common air leak locations. If the smoke wavers, you have likely found an air leak. Carry a notebook while you're doing this, perhaps with a basic map of your floor-plan, and mark the areas where you've found leaks, while making notes.

How to Air Seal Your Home

Once you have recorded the locations of gaps and holes in your home's exterior envelope, you're ready to proceed in learning how to air seal your home. Generally, caulk is best for sealing relatively small cracks in stationary locations (as opposed to doors and window sashes). Weatherstripping, on the other hand, is ideal for sealing moving components like the doors and operable windows themselves. Here's a look at how to use these tools to effectively seal your house against air leaks.

  • Caulking – When purchasing caulk to seal air leaks, consider that you will likely need about one half of a cartridge for every window or door that needs to be sealed, and four cartridges for your home's foundation sill. Because caulking compounds are available in various strengths, properties and prices, it's a good idea to talk to your HVAC professional about which compounds are best for specific areas around your home. Water-based foam sealants, for example, are good for small cracks, whereas polyurethane expandable spray foam is best for larger cracks in non-friction areas. Once the caulk has been purchased, you'll need to ensure that the area around each leak is clean and dry for maximum adhesion. The caulk should be applied consistently at a 45-degree angle. Do your best to avoid any stops or starts, and be sure to send the caulk compound to the bottom of the crack to avoid air bubbles. Make certain that the caulk is sticking to all sides of the leak. Any oozing caulk can be pushed back into the infiltration with a putty knife. Be mindful that the best time to apply a caulking compound is in a period of dry weather, when the temperature is above 45 degrees Fahrenheit.
  • Weatherstripping – They key to weatherstripping is learning how to air seal your home against leaks in moving components, while still allowing doors and windows to open and close freely. Also take care to consider factors such as friction, weather and other conditions that could cause wear and tear on your weatherstripping over time. In order to accommodate each specific leak of your home, you will need to find a product that will be able to withstand foot traffic, temperature changes, etc. Again, it's smart to talk to your contractor about which materials to utilize, or spend some time researching different weatherstripping products. Although felt and open-cell foams are usually susceptible to weather, the ease and cost-efficiency of applying this type of material can make it worthwhile in low-traffic areas. Vinyl is somewhat more expensive, but holds up nicely and is resistant to moisture. Metal products such as bronze, copper and aluminum are, by far, the most durable option for weatherstripping. To determine how much of each product you'll require for your air sealing project, add all perimeters of the windows and doors to be weatherstripped and then tack on an additional 5-10 percent to make up for any waste. Like caulk, weatherstripping should always be applied to clean, dry surfaces. Be sure to double-check all measurements before making a cut into the product, and work carefully to apply the weatherstripping snugly against all surfaces. When weatherstripping doors, the entire door jamb should be sealed, and one continuous strip should be applied on each side, making sure that the material is tight at all corners. For windows, the weatherstripping product should be applied between the sash and the frame. Be sure to test your doors and windows for operability after sealing them.

Don't Forget to Seal Your Ducts

When learning how to air seal your home, don't exclude your ducts. If your house utilizes forced-air heating or cooling systems, you could be losing 20 percent of the air flowing through your ducts to leaks and poorly sealed connections. This can create uneven temperatures, will raise your utility bills, and can put excess stress and strain on your HVAC equipment. Inspecting, sealing and repairing ducts can be challenging, as many are concealed in walls and between floors. These jobs are best left to the professionals. You may, however, be able to use duct sealant or mastic to seal exposed ducts located in attics, basements, crawlspaces and garages.

What About Ventilation?

Many homeowners mistakenly believe that some air leaks are necessary in order for their house to be properly ventilated. In reality, this is not the case. Relying on air leakage for ventilation is actually an unwise choice. This is because, as discussed previously, these gaps and cracks can reduce household efficiency and degrade the quality of your air's home. Leaks can also contribute to moisture problems, possibly leading to the growth of harmful mold and mildew. Ultimately, it's in your best interest to reduce as much air leakage as you possibly can. From here, you can work with your trusted HVAC contractor to evaluate your home's ventilation needs. Often, controlled ventilation through exhaust fans and whole-home ventilation systems can be the best solution for efficiency and health.

For more advice on how to air seal your home, contact the professionals at We proudly serve residents of Chicago, Northwest Indiana and Southwest Michigan.

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