Cooperative Living September 2015 - 13

ENERGY BANG FOR YOUR BUCK by Tom Tate, Contributing Writer
Stack Effect and
Your Home
C
hances are, if you are like the majority
of folks, stack effect is something
that has never crossed your mind. If
it has, perhaps it was in the context of the
Hasbro game, Jenga, where you carefully
remove wooden pieces from a stack and
place them on top until it all comes crashing
down. Well, in this case, it is something
altogether different.
Stack effect is the movement of air into
and out of buildings. It is caused by a temperature
difference between inside and outside
air that creates a pressure variation. This
pressure difference promotes the movement
of air from the high- to the low-pressure area.
For example, during heating season, the air
inside your home is warmer than the air outside.
Since warm air rises, as it moves up
through your home, it reduces the air pressure
inside your home and pulls in the colder
outside air to replace it. This is stack effect.
In the cooling season, the reverse
conditions and air flow exist. The cooler air
inside your home settles and flows outside,
drawing in the warmer air through infiltration
points at the roof. The Southern tradition of
opening the lower window sash on the cool
side of the house in the morning and lowering
the upper sash on the warm side is a
perfect example of stack effect being
managed by the home's occupants.
But, you ask, won't my efforts at sealing
my doors, windows and other openings prevent
this from happening? Proper weatherstripping
and sealing will greatly reduce
stack effect and will reduce your utility bills.
According to sources used in Wikipedia,
about one-third of HVAC energy consumption
comes from infiltration. Which is why we
always encourage our cooperative members
to diligently seal as many openings in the
exterior of their homes as possible. However,
unless your home was built to the newest
construction standards, you cannot completely
stop stack effect. There are simply
too many points in your home where air can
infiltrate to seal them all.
The truth is that you don't want your
home to become too airtight. Indoor air
quality (IAQ) will suffer when this happens.
September 2015/www.co-opliving.com
By the very act of living in our homes, we
create elements inside that need to be filtered
out or removed. Smoke from cooking, dust
from carpets, off-gassing of furniture and
other building components all contribute their
share. Plus, Mother Nature has some house
guests of her own, radon and mold to name
two, which need to be exhausted to the
outside or otherwise mitigated.
For proper IAQ, the American Society of
Heating, Refrigerating, and Air-Conditioning
Engineers (ASHRAE) recommends .6 air
changes per hour. This means that your home
should have 60 percent of the inside air
volume of the house exchanged with fresher
outside air each hour. Generally speaking,
the air exchange will occur through mechanical
ventilation intakes in the heating, ventilation
and air conditioning system (HVAC). This
allows your filters to remove a lot of outdoor
dust and pollen. Opening and closing doors
and windows is another major source of air
changes. And then there is our new friend,
stack effect.
Stack effect seems to be a double-edged
sword. On one hand it increases HVAC
energy bills and on the other contributes to
a healthier IAQ. Properly balanced and
sealed homes will take care of these issues,
providing you with the lowest possible
energy bill and highest possible IAQ. Why
not check with your HVAC contractor today
and see how they can help analyze your
home and recommend steps that will allow
you to achieve this balance?
11
YEN TEOH/HEMERA/THINKSTOCK
Cooperative Living September 2015

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