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The Air BoundaryThe Air Boundary should be continuous between the conditioned space of the home and the unconditioned spaces
that surround the home. If fact the air boundary of the home should parallel the thermal boundary. The difference
between the two is the thermal boundary deals with insulation and the air boundary deals with air leakage. You may
have heard or read about air sealing when insulating. When air leaves your home it takes your heating and cooling
dollars with it. In energy conservation this is a major loss and is the major source of discomfort in homes today. The question here is how to address this problem? In order to do that one has to understand the problem for one can address it. The best example is a balloon, if you blow air into a balloon it will get bigger and if you let air out of the balloon it will get smaller. What this means to you is that your home cannot get bigger or smaller. In other words, you cannot let air into the home without letting air out of the home. To take this a step further, let's say you have an average wood window and during the winter you put your hand around the window and you feel air coming in. You conclude that the window must either be fixed or replaced. If you think about it considering the above statements, what the drafts are really telling you is that the same amount of air that is entering your window is leaving your home. The air leakage (high-pressure area) represents your heating and cooling dollar loss. Though the air infiltration (low-pressure area) impacts your fuel bills and comfort levels, the air leakage is the source of the problem. There are ways to measure the airflow in one's home; the most common today is the blower door. Most companies use this to measure duct leakage. There are a few that measure the entire home and even go as far as zonal pressure testing with the blower door. The problem with this is that the blower door cannot distinguish between high and low pressure areas. The vast majority of the people in this industry will disagree with me on this issue. Their position is that the reduction of airflow in the home results in the lowering of fuel bills and increasing of comfort levels. They begin by air sealing in the attic in which there is agreement and the air sealing everywhere else until the minimum ventilation guides are met and this is where we disagree. In my opinion only the high-pressure areas should be air sealed. Take the example with the drafty window; let's assume the source of the air leakage was the whole house fan louver located in
the hallway. The solution is to put a piece of plastic over the louver and tape it air tight. After this is done you notice the
window still is drafty and the basement windows are too. You must then look for the air leakage or loss. You find that the
bathroom exhaust damper is so dirty that it does not close and the hole that the duct goes through is considerably larger than
the duct. You clean the bathroom exhaust and damper and seal up around the duct. Afterwards, you go back to the window and notice there are no drafts but the basement windows still are drafty. The minimum ventilation has not been met; therefore the window should be air sealed and not the basement windows. The reason for this is, prior to the air sealing of the louver and the exhaust, the window had air infiltrating it and afterwards the window had air leakage. The fact that the minimum ventilation has not been met and the window is no longer drafty indicates that it is a source of heat loss or air leakage. The blower door is an extremely effective measuring and verification tool and should not replace common sense when air sealing. For the average person in a home, you do not need a blower door to air seal. If your fuel bills are high and you are not comfortable all you have to do is look up. Since heat rises and it is the air in your home that carries the heat, look for anything in the ceiling that would allow air to escape. Examples of this are the access to the attic, plumbing, ceiling light fixture, electrical wires, drop ceilings in bathrooms, etc. The air boundary should parallel the thermal boundary for the same reasons as stated above. Another factor that should be considered is moisture. This not only applies to moisture you get on your windows during the winter or condensation in our attic, especially on cool surfaces like nails in your roof but also in your ceiling and walls. Whenever you heat air, it expands and when it cools, it contracts. This is what happens to the air in your home when the heat comes on and goes off. As with the example with the balloon, the house cannot expand and contract with the air. This is usually the primary source of air exchange in your home, which is good. Too much air exchange and the home is drafty and energy bills high. Too little air exchange and the home become unhealthy for the occupants. It is unlikely that the average energy bill payer could air seal their home to the point where there is insufficient air exchange. Usually the only way to bring down the air exchange to that point is when you construct the house to be like that. Then an air to air heat exchanger is installed to provide adequate air exchange. An example of a moisture problem concerning the air boundary is an outside wall outlet or a ceiling fixture. In most cases these areas are not sealed properly. When the heat comes on the air expands and goes out through the outlet and/or fixture. There are no cool surfaces there yet and the heat dissipates. Then the heat in the home cools and contracts. That brings air into the home through the outlet and/or fixture. The cold air coming into the home through the outlet and/or fixture begins to make the surfaces surrounding them cool. When the heat comes on and the air expands and goes through the outlet and/or fixture, the heat condenses on the cooler surfaces. You would be surprised to see how much those inexpensive electric outlet sealer and a can of foam will do you for.
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