How much outside air are you heating or cooling?

Here’s another explanation of air leakage to wrap your mind around.

Heat loss from infiltration is uncontrolled air leakage through joints in the construction and cracks around windows and doors. In the winter, the cold air that infiltrates the building is equal to the amount of hot air that escapes.

Conversely, in the summer, the cooler air inside escapes and hot exterior air infiltrates. Infiltration is caused by wind and stack-driven pressure differentials, which prompt air movement within the building envelope.

The infiltration rate varies greatly depending on the tightness of construction.

The blue box in the supplied video represents the building envelope, (i.e. the bit that is being heated or cooled).

The volume represented by this blue box is the amount of air that is to be heated or cooled. The question is, how many times do you want to heat or cool this volume?

At 2 Air Changes per Hour you will have to heat or cool it twice per hour. The problem is that the air that you are heating is replacement air that comes from outside. The outside air is at outside air temperature so the obvious conclusion is that you are heating or cooling 2 volumes worth of outside air every hour to meet the desired indoor air temperature!…..and we haven’t even considered the heat loss or gain through the conductance of the building envelope, (i.e. thermal performance).

LESSON: Air tightness is critical for energy efficiency. Keep the conditioned air inside and introduce fresh air on your own terms.

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