Much of our heating and cooling and overall comfort is lost through what we call in the building science performance contracting industry as infiltration and exfiltration. These are holes in our homes usually unknown and unseen. These holes add to our HVAC system load and negatively affect air quality or IAQ
Exfiltration is conditioned air escaping to outside our conditioned space. As this air escapes it must replaced. Where this make up air comes from depends on the house and conditions it is in.
Infiltration is air leaking into conditioned space from outside our conditioned space. Often this infiltration pathway is through unconditioned space like our attics garage and wall into conditioned space such as our living area. Some infiltration comes though the space of unsealed windows and doors.
Infiltration through doors and windows generally will have a negative impact on energy by having either colder or warmer air entering the space adding to the heating and cooling load, however can have a positive effect on Indoor Air Quality or IAQ by bringing outside or fresh air into conditioned space
Infiltration through unconditioned space is another story. It can not only negatively impact your heating and cooling load it does it to a greater degree. Our attics and walls have more extreme temperatures within them. That air making its way into conditioned space causes the load to go up significantly. Furthermore it brings a whole host of containments with it severely compromising our IAQ . This is especially true of air from our attics.
Our attics are open to outside via gable and Sofit vents. Over the years all the dust dirt pollution and other debris settles into our attics. When our space has infiltration from our attic it brings all these unwanted particles with it into our living and breathing space.
The stack effect can enhance the infiltration and exfiltration