by Don Ames, www.detectenergy.com
Air sealing is important because air leaks through the walls, floor, and ceiling of your home. Air leaks out of your home when the air pressure inside the home is greater than the air pressure outside the home. Air also travels from hot to cold. The bigger the hole and the greater the pressure or temperature difference, the more air leaks.
Air Sealing is restricting the passage of air through the walls, floor, or ceiling so the home is more energy efficient and the process of heating or cooling the home takes less energy and less money.
Remember your Mother yelling at you as you flew out the back door, “Harvey, shut the door, we don’t want to heat the whole outdoors.”
Well, if you knew how many air leaks were actually part of your home, you would be interested in sealing them just like your interested in getting the door closed after Junior heads for the neighbors.
Although you find obvious air leaks, it is the large hidden penetrations that dominate air leakage. Air leaks can be rather straight forward, passing directly through a wall, floor, or roof at one location. Or they can be indirect, beginning at one location and exiting at another.
Have you every felt cold air coming through a light switch on an interior wall? Now, that’s an indirect air leak.
Air sealing is education and testing. Education, because it takes an understanding of how a wall, floor, or ceiling is constructed to effectively search and locate hidden air leaks. Testing, because the amount and location of air leaks can be determined. Testing also allows you to see the effectiveness of your air sealing efforts.
To control air leakage, an effect air barrier should border and touch the insulation. Without an effective air barrier, air is allowed to pass through and around the insulation which greatly reduces the effectiveness of the insulation.
Existing homes may have several partial air barriers. For example, a home may have interior wall paneling, insulation, exterior sheathing, and then siding. These wall components merely slow down the passage of air rather than stop it. Irregularities in the homes exterior shell will promote air leakage as there is often a problem where building materials join together.
Air Sealing is providing appropriate retrofit applications that repair the original construction condition of your home that reduces the direct and indirect air leakage. Special attention needs to be given to rim joist, overhangs, dormers, bay windows, balloon framing, chimney’s, knee walls, and storage attics.
Materials used for providing effective air sealing and air barriers include kraft or asphalt paper, plastic sheeting, house wrap such as typar or tyvek, caulk, spray foam, foam board, metal flashing, plastic bags, styrofoam, mastic or anything else that you have that gets the job done.
Stack Effect is a natural force that drives air leakage. Warm air is less dense than cold air, so warm air rises and cool air replaces it. Stack effect takes place 24 hours a day, 7 days a week. Warm air leaves your home by passing through the holes and penetrations in the ceiling or roof. Cooler air enters the home through holes and penetrations near the floor.
Air sealing is addressing the energy waste caused by Stack Effect. Holes and penetrations in both the ceiling and floor are sealed so warm air can not escape and so cold air cannot take it’s place. Restricting the energy waste caused by Stack Effect can greatly reduce your power bill.
Penetrations and fenestration’s are holes that were made in your home by a variety of well meaning contractors. The Plumber cut a bunch of holes for pipes and the electrician cut a bundle of holes for wiring. The Heating Contractor cut a number of holes for ducts and flues and the window and door contractor cut some huge holes for windows and doors. In fact, all the holes in your home were man made.
Air Sealing is following around behind the plumber, electrician, HVAC, and other “Professionals” and sealing up all the holes they left. You grab a can of “Great Stuff”, spray foam insulation, and follow the wire or pipe until you get to a wall, floor, or ceiling and then you fill the resulting hole. This is like a scavenger hunt or perhaps the reenactment of the Hansel and Gretel story. When you find a ½ inch pipe going through the floor by way of a 3 inch hole and you fill the 3 inch hole with insulating Great Stuff, you feel like you just kick part of the wicked witch in the fire. It feels good.
A blower door is a piece of testing equipment that can be used to provide data on the amount of air leakage that occurs in your home as a result of air leaks. The leakage is represented in cubic feet of air per minute. ( CFM ). A cubic foot of air is about the size of a basketball.
A duct blaster is also a piece of testing equipment, but in this case, the duct blaster provides data on the amount of air that is leaking through the walls of the ducts on a forced air heating or cooling system.
Sealing the air leaks in the duct system is one of the most beneficial and most cost-effective, energy saving measures you can complete.
Air sealing is something you do before you install additional insulation in the attic and before you install that new high efficiency gas furnace. Air sealing is something you pay extra attention to when you are having new, energy efficient, windows installed. Air sealing is something you do after the Home Energy Auditor tells you that the blower door indicates there is 2,562 cubic feet of air leaking into and out of your home every minute.
Air sealing is having the Energy Auditor tell you that the duct blaster documents there is duct leakage to the tune of 600 CFM of conditioned air leaving your heating ducts every minute. Air Sealing is seeing the duct leakage reduced to 80 CFM and realizing that your furnace does not run as often or as long and the power bill this month is less than it was last month.
MVL stands for “Minimum Ventilation Level”. This is a study that supports the fact that you and I can not live in a plastic bag. In other words, if we seal up all the holes and penetrations in our home so that no air can get in or out, it would be like living in a plastic bag. The home would not be a healthy place to live.
If you get over excited with air sealing and you end up reducing the MVL below healthy standards, you may need to provide controlled air leakage. Controlled air leakage can be provided by mechanical devices like ceiling exhaust fans or heat recovery ventilators. Controlled air leakage can also be provided by opening a window or having the neighborhood kids over for a snack.
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