As much as 20 percent of summer heat enters your home as sunlight shining through windows. To cut "solar gain," add curtains or blinds to rooms that get direct sun and draw them in daylight hours. With the shades drawn, a well-insulated house will gain only 1 degree per hour when outdoor temperatures are above 85 degrees.
Pay special attention to west-facing rooms late in the day. Shades and blinds to consider include roller shades (the least expensive option), venetian-type micro-blinds, reflective curtains and insulated curtains (the most expensive, at $100 per window). Two exterior options are to install awnings or plant shade trees.
Cost: $8 to $100 per window
Benefit: Up to 20% of your cooling bill