From Home Energy How-To , a Popular Science book
by A.J. Hand, copyright 1977 by the author and reprinted
with the permission of Harper 8 Row Publishers, Inc.
Available in hard cover ($9.95) from any good
"In a recent four-year period," says A.J. Hand, a former
how-to editor at Popular Science magazine, "the number of
U.S. homes with central air conditioning tripled. For much of
the country—though—there are cheaper, more
energy-efficient ways to keep cool."
And in the "Home Cooling" chapter (reprinted here in its
entirety) of A.J.'s book, Home Energy How-to, you'll find
detailed explanations of some of those ways to beat the
heat, cut costs, and reduce energy use—all at the
same time!—this coming summer.
Americans use more electricity just to run their air
conditioners than is produced in all of China. And, while
not so many years ago we all got along fine
without air conditioning, today most Americans
consider it a necessity rather than the luxury it is.
Luxury or necessity—however you classify air
conditioning—the fact remains that it consumes a lot
of electricity. And it's an area of energy use that's in
great need of conservation measures.
The air conditioner manufacturers realize this, and they're
doing everything they can to make more efficient products.
You can do your part too. First of all, don't buy or use an
air conditioner unless you really need one. There are
cheaper, less energy-consumptive ways of keeping cool,
which we'll discuss later In this article. By all means try
them before you turn to air conditioning. Even if they
don't solve your cooling problems entirely, they'll still
take some of the load off any air conditioner you decide to
use later . . . saving energy and money all the while.
RATING ENERGY EFFICIENCY
If you decide you really need an air conditioner, think
small, because refrigerating an entire house Is wasteful.
Small window units can cool one or two rooms to which you
can retreat when the rest of the house gets uncomfortable.
And while you're thinking small, think "efficient".
The efficiency of an air conditioner is expressed by a
number called the Electrical Efficiency Rating (EER). The
EER is simply the cooling capacity of the unit in Btu's,
divided by the unit's wattage. All air conditioners sold
today must have the EER labeled on the machine. But if you
buy a used unit with no EER label, remember that you can
compute the rating yourself simply by dividing Btu's by
What's a good EER? Well, it varies with unit size. Tiny
portables might be considered good at an EER around seven,
but a large room unit would have to rate over 10 before it
could be considered highly efficient. Central units peak at
around 10 or 11.
If you want to figure how much it will cost you per year to
run an air conditioner, multiply the unit's wattage rating
by the hours the unit runs (1,000 is about average), then
multiply again by your cost for electricity in dollars per
kilowatt hour. Divide this number by 1,000 and you have
your yearly operating costs.
Extra efficiency almost always costs you extra money: A
higher EER means a higher initial purchase price. If you
want to find out how many years it takes a high-efficiency
unit to pay back its extra cost over a cheaper, low-EER
machine, just compute yearly operating costs for both
machines as described in the preceding paragraph. Then
divide the yearly savings of the more efficient unit into
the difference in purchase price between the high and
Chances are you'll find the high-efficiency unit pays off
in three to eight years in the South, where air
conditioners are run more frequently. But it may take 20
years for such a machine to pay for itself up north. Since
the life span of a typical air conditioner is only 10 to 15
years, the high EER wouldn't pay off. But if you live where
it takes this long to make up the difference, you really
don't need an air conditioner anyway since you'll only be
using the machine about eight days a year.
Of course all these calculations are based on the
ridiculous assumption that your electrical rates will
remain stable. No doubt, however, they will rise . . . and
as they rise the economics of the efficient unit get better
Buying the right size air conditioner is important,
and—fortunately—it's better to err on the small
side than it is to get one that's too large. This is
because much of an air conditioner's ability to keep you
cool comes from its dehumidifying abilities. A large unit
cycles on and off so often that it never gets a chance to
dry the air. A smaller unit, on the other hand, will run
longer each time it turns on and will do a much better job
of dehumidifying. While your dealer can help you select the
right sized unit for your needs, you can do an accurate job
yourself by consulting a copy of the "Cooling Load Estimate
Form", available from the Association of Home Appliance
Manufacturers, 20 N. Wacker Drive, Chicago, III. 60606.
TUNING YOUR AIR CONDITIONER
If you have to use an air conditioner, you should always
keep it in tune. This is a simple job consisting of a few
easy steps, many of which need be performed only once a
year. Other steps—such as cleaning
filters—should be performed at least monthly.
If you have central air conditioning, shut off all the
power to the unit. Then check to make sure the fan belt on
the blower is properly tensioned. Press down on the belt
halfway between the pulleys and measure the deflection. It
should run around 1/2 to 3/4 of an inch. If the belt is
loose, tighten it. But if it's too tight it can create
excessive loads on the bearings, so don't overdo things.
Air conditioning requires a greater flow of air than
heating does. If your blower has an adjustable pulley, make
sure it's set to run at the highest speed. To make the
adjustment, loosen the set screw on the pulley and twist
the outer flange so that it is as close as possible to the
inner flange. This narrows the pulley and forces the belt
to ride higher. Check belt tension after making the
Clogged filters are probably the biggest wasters of energy
your cooling system has to tolerate. Filters should be
cleaned or replaced once a month, but most homeowners don't
do the job at all. While you're in the cleaning mood, clean
the condenser and evaporator coils. Use a commercial coil
cleaner, available at a refrigeration supply house. And
when you're there, pick up a fin comb . . . a simple
plastic tool used to straighten bent fins.
To use the cleaner, spray it onto the coils and fins and
let it set for about 10 minutes. Then rinse with a hose or
a spray of clean water from a squeeze bottle. If the coils
are still dirty, give them a follow-up treatment. To use
the fin comb, match the teeth-per-inch rating on the comb
to the fins per inch on your air conditioner's coil. (The
comb will have different sections with varying teeth
spacing.) Then run the comb through any bent fins.
Last, check to make sure that airflow over your air
conditioner's outdoor condenser coil is not blocked by
bushes or other vegetation. Shading the condenser will
raise efficiency about two percent, as long as the airflow
is not blocked. Small evergreens planted a safe distance
away from the condenser will provide the shade. Just be
sure to prune them back if they begin to choke oil air to
Room air conditioners should get the same treatment as
central units. Clean the filters and coils, and oil the
motor if it has oil fittings. Straighten bent fins, and
check outdoors to be sure the airflow through the unit is
not being impeded.
If you have a window unit, and if it has adjustable louvers
to direct its airflow, set them to force the cool air
upwards. Cool air naturally drops to the floor. Aiming it
upwards will help distribute the air before It has a chance
to stagnate at your feet (Unimpeded airflow is just as
important inside the house as It is outside. Be sure no
furniture or curtains block the air conditioner's output of
Central conditioning units can be adjusted to distribute
cool air just where you need it. With central heating, one
can adjust dampers in the ducts to provide warm air to
those rooms that should have it the most, and you can do
the same thing with central air conditioning.
Rooms requiring one setting in winter will require a
different setting in summer. So you'll have to change the
damper adjustment every time you switch a central
heating/cooling unit from heating to cooling. That's why
it's a good idea to mark the position of the damper handle
once you've found its ideal setting for winter heating.
Then mark it again at its best setting for summer cooling.
Remember, too, that it's best to close down the dampers in
ducts leading to rooms that need little cooling. This will
provide more cool air to the rooms that need It most. The
general rule is that rooms where there is a lot of activity
or heat (the kitchen, for example) will need the most
Most air registers are located near the floor. This is fine
for heating, but not so good for cooling. The cool air
tends to come out at floor level and just stay there until
It's picked up by the return air duct and routed through
the cooling system once again. You keep recycling the same
cool air over and over this way, and it never gets high
enough in the room to have any cooling effect on most of
your body. You can remedy this situation to some degree by
installing clip-on or magnetic baffles over the central air
conditioning system's registers, to direct the airflow
upwards. (Of course you'll want to take these off during
the heating season or you'll wind up with all the hot air
hugging the ceiling during the winter.)
An even more effective way to spread cool air throughout
all levels of a room is to use a high-return air duct
system. With this method, a return air duct is placed up
high—near the ceiling—where it draws off the
hottest air in the room and sends it to the air conditioner
To install a high return duct, remove the finished wall
surface between the two studs that straddle a return duct
mounted low in a wall. Then install a sheet metal liner or
rectangular duct leading from the low duct up to a position
near the ceiling. Install a new register grill at the high
return and cover the wall again.
Now you can switch between the high return for cooling and
the low return for heating by closing off one or the other
with a metal plate. Or you can install grills with built-in
dampers to achieve the same effect.
THERE ARE ALTERNATIVES TO AIR
There are many other techniques that will increase the
summer cooling efficiency of a house. Adequate
weatherstripping and Insulation, duct insulation, caulking,
and such window adaptation ideas as double glazing,
application of light control film, and installation of
storm windows will all provide warm-weather benefits as
well as certain wintertime advantages.
And there are some other ideas for cooling that may well
eliminate the need for air conditioning altogether.
Probably the most important is proper attic ventilation.
During the summer, temperatures as high as 130 degrees are
not at all uncommon in an attic. This heat, in effect,
turns your ceiling into a radiant heater. With proper
ventilation—either natural or fan-induced—you
can drop attic temperatures way down. Most effective are
fans installed near the peak of a roof, and controlled by
thermostat. The 'stat will turn the fan on at a temperature
usually around 110 degrees, then cut it off when the heat
drops to about 95.
Roof-mounted vents are more effective than gable-mounted
fans because you can position them near the midpoint of a
roof's length. Most are sized to fit right between the
rafters, so installation is quite simple. Just cut a hole
through the roof and place the unit in position, slipping
the attached flashing up under the shingles. Then, inside
the attic, wire the fan to a junction box. For best
results, the fan should be teamed up with soffit vents.
Installing gable fans is usually even simpler since there's
no need to cut through the roof.
Natural attic ventilation can be increased by installing
ridge vents or turbine ventilators. Ridge vents provide a
continuous—though weatherproof—opening for the
full length of a roof's peak. The total free or open area
of the roof vent should then be matched by an equal area of
soffit venting to provide a free flow of cooling air. The
total area of roof and soffit vents should be equal to at
least 1/300 of the attic floor area, and twice that much
vent area is even better. In addition to carrying off hot
air, vents also exhaust humidity, which provides another
Before air conditioning came along, ventilation was the
only way to cool a home. You can set up ventilating air
currents with a fan or rely on natural powers of
convection. The trick is to bring in cool air near or below
ground level and exhaust it from the attic.
Convection or stack cooling relies on the hot air within
your home rising and creating a chimney or stack effect.
For best results, open your basement windows to let in
cool, close-to-the-ground air.
Once the cooler air is in the house, it should have an
unrestricted path through which to travel. Open the door at
the head of the basement steps, make sure all interior
doors are open, and open the door to the attic. If your
attic has no door—just a hatch or a folding stairway
that will inconveniently block up a hallway—put a
screened hatch in your upstairs ceiling. Last, provide some
way for hot air in the attic to escape. Roof vents, gable
vents, ridge vents, or a turbine ventilator will all help
get the air moving.
If you decide to use fans or powered vents, it still pays
to set your home up as described. The stack effect will
relieve the fan of some of its work and help encourage
better airflow. Remember, ventilation can help cool your
home by getting rid of trapped heat, but it will not make
your home any cooler than the temperature outside. On the
other hand, the slight breeze created by ventilation will
make your home feel cooler than the thermometer might
Everyone knows that a white roof is cooler than a dark one.
It reflects a substantial part of the sun's energy. But did
you know you can change the color of roofing without
reshingling? Roofing paints are the secret. They can go on
over shingles, roll roofing, even metal, and can add years
to the life of the roof . . . by virtue of both protective
coating and reflective cooling. Most large paint stores
carry roofing paints, as do Sears and Montgomery Ward.
If you happen to have a well, spring, or other source of
cool water on your property, you can cool your home very
effectively without running an air conditioner. One fellow
refrigerates his six-room Oklahoma house by pumping well
water through three automobile radiators housed in a wooden
box outside one of his windows. A squirrel-cage fan forces
air through the radiators and into the window. Even in
100-degree weather this system keeps his home's temperature
down to 70 degrees. Water at 59 degrees is pumped through
the radiators at a rate of about 500 gallons per hour, and
circulated water is returned to the ground via a second
Water can cool your home another way: If you fasten a
simple sprinkler-type hose—upside down—to the
peak of your house's roof, you can use it to trickle water
down the roof and set up an evaporative cooling cycle.
Connect the sprinkler to an outdoor bib and adjust the flow
to use as little water as possible . . . just enough to
keep the roof wet down to the eaves is best.