Many air leaks and drafts - like those around the sashes of the windows or at the bottom of the doors - are easy to notice and to feel; but many of the most significant air leaks in wood frame single-family homes are hidden in the attic and basement and may involve unsuspected paths.
You should try hard to find possible leaks around the framing members of the house, light fixtures, pipes, wires, fireplaces and chimneys. That's very important for home energy improvements.
Air leakage points can be hidden. In some cases, big air leaks - located in the attic and basement – can go unnoticed. But they are the most critical.
Basement and Attic Air Leaks and the Stack Effect
Attic and basement leaks are in close relationship, in wood frame homes. That's a fact that many people do not notice or do not know.
During the winter, the indoor heated air raises and when it finds any opening in the ceiling, it will escape to the outside. And when it escapes, fresh outside air will be pulled into the house through leaks at the bottom of the house (namely in the basement).
That’s the well-known chimney or stack effect, responsible for huge heat losses (see image at right, from Energy Star: the red arrows show the heat loss, and the blue arrows the infiltration of cold outside air).
But there is also a summer stack effect, well less known, also involving the attic and basement air leaks.
In this case, the outside hotter air enters the house through attic leaks, making the heavier colder air to sink and to leak out through the bottom of the house.
That’s the stack effect in reverse, a mechanism often ignored, but also with a huge impact, this time in the air conditioning bills.
When people leave upstairs windows open in a summer day, thinking that the hot air will escape through them (according to the principle that hot air rises and escapes through upper openings), they are wrong and may be drawing in hot outside air.
The stack effect (in their winter and summer versions) is a powerful mechanism that alone explains how energy losses can happen, and the role of air leaks in them.
Our video On The Stack Effect:
Other air leaks
In homes without attics and basements, things are less serious. Air leakage can be responsible for minor drafts and some discomfort, and should be addressed, but its impact may not be very significant.
That's namely the case of small air leaks around the window sashes, or due to poor window weatherstripping, or air leaks at the bottom of doors. Though they should be fixed, they aren't as important as people sometimes think.
Often more important are air leaks through flaws in the framing of the house, in wood and steel-framed construction.
The top and sill plates of interior and exterior walls can be the way through which large amounts of air is driven into or out of the house, and should be properly sealed with spray foams or caulks.
Also do not forget the chimneys and fireplaces, and possible cavities around them (often opening to the attic). They too can be a source of important air leaks.