The primary way to plant the trees right deals with location, McPherson says. "If you can locate one tree anywhere, the west side of the home is best," he says. "The east side would be your second preference."
The reason why the west gives the most savings is because it is warmest in the afternoon as the sun is getting lower in the western sky. The sun is shining through western windows. That is also the time that people are coming home from work and turning on their air conditioning.
"You get the biggest bang for your buck when you plant in the west," McPherson says.
It is important also to plant a deciduous tree — a tree that sheds its leaves in the fall. That is because having the sun heat up the home is bad in the summer, but important in the winter. Planting an evergreen in that location will increase the heating load in winter.
Planting trees on the south doesn't have the same beneficial effect economically. McPherson recommends choosing trees on the south that drop leaves early and leaf out late in the spring so the sun can start warming the house as the weather turns cooler.
It is true that the branches of trees that shed their summer leaves will give some shade to a home in the winter, but Sarkovich says the savings benefits accumulated in the summer by cooling the home far exceed any loss of the sun's warmth in the winter.
Smaller trees that shade air conditioners may also help. Sarkovich says shielding air conditioners from the direct rays of the sun may extend the life of the condenser and save some energy because the air conditioner doesn't have to work as hard.
Of course it may take a few years for trees to mature enough to have a bigger impact. But there are other benefits.
"Just seeing a tree and urban greenery reduces stress and helps people to relax and recover from fatigue," says McPherson.
And that is a different type of cool.