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Air Infiltrations

What is Air Infiltration?

Air infiltration refers to the air that comes in or “infiltrates” into your home from outside. Unless a building has a planned and regulated fresh air supply system, they all need some infiltration. The people inside the building need fresh air to breathe and infiltration is how they get it. There are however, limits. It has been found that one complete air change every three hours is acceptable for the persons inside to have enough fresh air. We of course, have a way to test and measure this air infiltration and can then quantify it. A blower door is used which pressurizes or depressurizes the building. A handheld computer can then determine how much air leakage a building has by how fast the fan must turn to keep the pressure at a steady rate. The test results are read in CFM50 or Cubic Feet per Minute while at a test pressure of 50 Pascal.

Air Sealing IllustrationIt’s very seldom we find a building in its natural state that has test results at or even close to the ideal three air changes per hour. We usually find leakage (infiltration) numbers twice or three times the target.

Improve your Indoor Air Quality

Most of this excess air comes from the attic, which isn’t the cleanest air to breathe. When your home is built it’s framed with green (wet) lumber. The drywall is nailed to this green lumber and over the course of years as the lumber dries it shrinks. The method used to secure the drywall at the top of the wall does not allow the drywall to move with the shrinking wood. So a gap develops between the wood of the wall top plate and the drywall. At most every wall. So attic insulation should either be removed or pulled back from the area above the walls and this gap sealed with spray foam or caulking. Another area of infiltration is under kitchen and bathroom sink cabinets where the plumbers drill 4” holes to run a ½” pipe thru them. And of course any wooden exterior doors that show light when closed and locked should be weather stripped. Air sealing can be a DIY thing.

DIY Air Sealing

Air Sealing is one of those things that a person with a bit of mechanical ability and a few hand tools can do themselves. Again though, a qualifier is in order. We don’t mean to imply that everybody can or should be doing this. There are some people who just aren’t good with sharp tools, or have trouble balancing on a ladder.  So respect your limitations.

After beginning to air seal a home you should have a blower door available to test while the work is being done. There are two main reasons for this. The first, if you depressurize the building and start a blower door running, it becomes fairly easy to locate leaks. With air coming into the structure you can feel the air on the back of your hand. Or you can use a smoke pencil. 

You also want to check the blower door number while doing the work so you don’t air seal down below 70% of the target. If you air seal a home below 70% of the three air changes per hour you must then provide enough mechanical ventilation to bring in 100% of the calculated replacement air. 

Ensure Optimal Air Flow

A recent change in the code has mandated each new home have a fan that is quiet enough to run 24/7 and sized to supply that three air changes per hour. Then a house can be made as air tight as possible and it will still get enough replacement air. People do this so they can control where their breathing air is coming from. They can also add a filtration device to the fan. Or better yet they can install an HRV which is a Heat Recovery Ventilator. It bring is enough fresh air and can filter it but also recovers most of the heat from the inside air and heats the fresh air coming in with it so almost no heat is lost in the process.  

To learn more about air infiltration and air sealing or to schedule a home assessment, contact us today!