Defining
the Thermal Envelope
The
thermal boundary, oftentimes called the thermal envelope, refers
to the parts of the building which separate indoor space which
is heated or cooled, from the areas that are not heated or cooled.
Sounds simple right?
These
spaces are referred to as the conditioned space, and the purpose
of your air conditioner or heater is to maintain the temperatures
in these areas at comfortable levels.
Howerver,
the thermal boundary is not the same as the weather shell of
your house. Although it may coincide in many places, they have
very different purposes and are not usually located in the same
spot. The weather shell is designed to shed rain, wind, and
snow in effort to keep it's contents dry. For example, the roof
is usually part of the weather shell, but is not included in
the thermal envelope as most of us do not heat their attics!
Garages are another good example, as they are part of the weather
shell, but only the wall between the garage and the living space
is part of the thermal boundary.
Insulating
a House
Heat
loss through the ceiling and walls in your home could be very
large if the insulation levels are less than the recommended minimum.
When your house was built, the builder likely installed the amount
of insulation recommended at that time. Given today's energy prices
(and future prices that will probably be higher), the of insulation
level might be inadequate, especially if you have an older home.
If
the attic hatch is located above a conditioned space, check to
see if it is at least as heavily insulated as the attic, is weather
stripped, and closes tightly. In the attic, determine whether
openings for items such as pipes, ductwork, and chimneys are sealed.
Seal any gaps with an expanding foam caulk or some other permanent
sealant.
Sealing
Air Leaks
While
you are inspecting the attic, check to see if there is a vapor
barrier under the attic insulation. The vapor barrier might be
tarpaper, Kraft paper attached to fiberglass batts, or a plastic
sheet. If there does not appear to be a vapor barrier, you might
consider painting the interior ceilings with vapor barrier paint.
This reduces the amount of water vapor that can pass through the
ceiling. Large amounts of moisture can reduce the effectiveness
of insulation and promote structural damage.
Make
sure that the attic vents are not blocked by insulation. You also
should seal any electrical boxes in the ceiling with flexible
caulk (from the living room side or attic side) and cover the
entire attic floor with at least the current recommended amount
of insulation.
Checking
a wall's insulation level is more difficult. Select an exterior
wall and turn off the circuit breaker or unscrew the fuse for
any outlets in the wall. Be sure to test the outlets to make certain
that they are not "hot." Check the outlet by plugging
in a functioning lamp or portable radio. Once you are sure your
outlets are not getting any electricity, remove the cover plate
from one of the outlets and gently probe into the wall with a
thin, long stick or screwdriver. If you encounter a slight resistance,
you have some insulation there. You could also make a small hole
in a closet, behind a couch, or in some other unobtrusive place
to see what, if anything, the wall cavity is filled with. Ideally,
the wall cavity should be totally filled with some form of insulation
material. Unfortunately, this method cannot tell you if the entire
wall is insulated, or if the insulation has settled. Only a thermographic
inspection can do this.
Windows
and Doors
If
your basement is unheated, determine whether there is insulation
under the living area flooring. In most areas of the country,
an R-value of 25 is the recommended minimum level of insulation.
The insulation at the top of the foundation wall and first floor
perimeter should have an R-value of 19 or greater. If the basement
is heated, the foundation walls should be insulated to at least
R-19. Your water heater, hot water pipes, and furnace ducts should
all be insulated. For more information, see our insulation section.
Heating
and Cooling Systems - Plus HVAC Ductwork
Inspect
heating and cooling equipment annually, or as recommended by the
manufacturer. If you have a forced-air furnace, check your filters
and replace them as needed. Generally, you should change them
about once every month or two, especially during periods of high
usage. Have a professional check and clean your equipment once
a year.
If
the unit is more than 15 years old, you should consider replacing
your system with one of the newer, energy-efficient units. A new
unit would greatly reduce your energy consumption, especially
if the existing equipment is in poor condition. Check your ductwork
for dirt streaks, especially near seams. These indicate air leaks,
and they should be sealed with a duct mastic. Insulate any ducts
or pipes that travel through unheated spaces. An insulation R-Value
of 6 is the recommended minimum.
Lighting
and appliances
Energy
for lighting accounts for about 10% of your electric bill. Examine
the wattage size of the light bulbs in your house. You may have
100-watt (or larger) bulbs where 60 or 75 watts would do. You
should also consider compact fluorescent lamps for areas where
lights are on for hours at a time. Your electric utility may offer
rebates or other incentives for purchasing energy-efficient lamps. |
