HOME HEAT LOSS - HOW AND WHERE
Heat energy escapes from your home primarily in two ways, through
air leaks and by inadequate or defective insulation. First lets look at
heat loss by air movement.
Air movement associated with heat loss through your home is caused by three main
forces: the stack effect, mechanical systems and wind. The most prevalent cause is
by the stack effect. Simply put, warm air rises when surrounded by cold air, i.e., the
heated air in your home wants to rise when surrounded by the cold outside air.
During the heating season your home experiences similar pressures to that of a hot
air balloon. As the illustrations below points out, this rising heated air escapes
through the top of the building envelope thus creating low pressure in the lowest
levels of your home and drawing in cold air. See below for illustrations and
additional text from Department of Energy.    
Escaping heated air and intruding cold air through the building envelope
What is a home envelope?
The exterior of your home is also called the "envelope" or shell. (See the orange line showing
the envelope in the diagram.) The insulation, outer walls, ceiling, doors, windows, and floors all
work together to control airflow in and out of the structure, repel moisture, and prevent heat from
being lost or gained inside your home. A high-performance envelope helps maintain a
consistent temperature even under extremely hot or cold conditions. The goal of Home Sealing
is to improve the home envelope to make homes more comfortable and energy efficient.
Heat Loss by Inadequate or Defective Insulation
R- Value = Thermo Resistance (Duel Effect)
The greater the R-Value of the thermo envelope the less energy it takes to heat and also cool
your home. Every measure taken to improve the building's thermo resistance to heat loss also
results in reduced cooling cost during the warm summer months.  
Please revisit our site for
future information on
Windows, Heating Systems,
Basements, etc., and for
'How To' information for
DIY home owners.

Should you have questions
regarding home energy
topics please feel free to
email at the above
provided link.


Before adding insulation to your attic it is beneficial to air seal beforehand. This is because
fiberglass and lose fill insulations will not stop air flow (heated air loss) and it is much easier to
locate and correct these leak points before adding insulation. The existing insulation in your
attic should be evaluated in terms of its current effectiveness. Rolled and fiberglass batt
insulation performance can be significantly reduced if incorrectly installed which is common.
Also common is displaced insulation due to remodeling projects, upgraded electrical fixtures
and even animal infestation. These potential issues should be resolved before adding
additional attic insulation.

Side wall insulation is not nearly as accessible and open to evaluation as other areas of the
building envelope, but is visible with infrared. Common defects are caused by settlement and
in the case of many older homes built before the 1960's, no sidewall insulation at all.
Conductive heat loss through uninsulated side walls can represent a significant heating and
cooling load, and its usually cost effective to add insulation.

See Demo Report at the Home Page for actual examples of insulation deficiencies from one of
our inspection reports. See the Department of Energy guides to Insulating Your Home and
Home Sealing Also, see Resources above for the shortcoming's of Loose-Fill Fiberglass attic
insulation.



Very leaky houses are uncomfortable and have high energy bills, so finding and curing
infiltration problems is a high priority for weatherization operations. The rate of air infiltration in
a home depends on many factors, the most important being the size and location of holes in
the thermal envelope and the difference in temperature between inside and outside. Warm air
inside a dwelling gives rise to stack-effect infiltration as it tries to escape from the top of the
envelope, sucking in cold air at the bottom. Wind and leaks in duct systems can also have a
major effect on infiltration, but these effects are not usually as constant over the heating season
as is stack­effect infiltration, which is at its worst on coldest days.

Note that in the middle of the heated envelope there is a neutral pressure zone where neither
infiltration nor exfiltration occurs due to stack effect. This explains why caulking and weather
stripping in mid-envelope tends to save less energy than careful attention to the bottom and
top of the envelope, where these natural driving forces are greater.
Attic
Fan
- 2ND STORY FLOOR JOIST
- FIREPLACES
- ATTIC ACCESSES
- BAND JOIST
- 2ND STORY HALF-WALLS
Heat Loss

Heat Loss by Air Movement
Infiltration of Outside Air in Winter
Where to Insulate
BAND JOIST