One VERIFY viewer sent us a question about adding a shade over a home’s central air conditioning unit outside.
“It's been going around social media that keeping your air conditioner shaded by an umbrella reduces power costs and helps it to run more efficiently,” said Jennifer in an email. “Is this true?”
Does putting a shade over your central air conditioning unit outside reduce power costs and help it run more efficiently?
No, putting a shade over your central air conditioner’s outside unit does not reduce power costs or help it run more efficiently. However, shading can be effective for a window unit A/C.
WHAT WE FOUND
Putting a shade over the outdoor unit of a central air conditioning system, which is the kind that cools an entire home, doesn’t improve energy efficiency in a noticeable way. It can even restrict airflow and make the air conditioner run less efficiently, experts say.
“It's not statistically impactful,” said Wes Davis, the technical services director for the Air Conditioning Contractors of America (ACCA). “That’s the short answer.”
Davis referenced a 1996 study conducted by the Florida Solar Energy Center which found that localized shading over the central air conditioning unit provided a maximum 3% decrease in electricity consumption.
“Our measurements did not allow us to conclusively determine that A/C condenser shading, when limited to the immediate area surrounding the condenser unit, provides statistically consistent reductions to cooling energy use,” the study’s authors wrote.
Not only is there little benefit to shading the area immediately around the A/C unit, shading it also risks making the unit perform worse. That’s because the method of shading, like a tarp or umbrella, could restrict airflow to the unit.
The A/C in a central air system works by first pulling the air from inside of your house and separating the heat from it. It then sends the heat out to the condenser, which is the box with a fan that sits outside of your house. The condenser's fan pulls the outside air into the unit, and that air then absorbs the heat before it's dumped back outside of the unit.
A/C units are engineered to do this with a certain amount of air flowing over the coil and fan, Energy Vanguard, a firm that focuses on training and consulting for building performance, says. Objects placed directly overhead of the unit, like an umbrella or a tarp, or plant debris cluttering the fan at the top of the unit, restrict the airflow and trap the heat over the unit.
“If less air flows over the coil, less heat is removed,” Energy Vanguard says. “That means the whole cycle warms up a bit, and your AC works harder to keep your home cool.”'
But while localized shading can’t accomplish much, it’s not a bad idea to take advantage of more widespread shading for your A/C and home alike.
“The preferred strategy may be a long-term one: locating A/C condensers [the outside unit] in an unobstructed location on the shaded north side of buildings and depending on extensive site and neighborhood-level landscaping to lower localized air temperatures,” the authors of the Florida Solar Energy Center study said.
Even though the benefits are minimal, it doesn’t hurt to place your air conditioner so it’s on the shadiest side of your house, if you have the option to move a unit or install a new one. Davis said his is on the east side of his home, so that as the sun moves from east to west across the day, his home is shading the A/C unit when the day is at its hottest.
The real benefits come from shading your entire home — this is what the study meant when it said to use “extensive site and neighborhood-level landscaping to lower localized air temperatures.” The U.S. Department of Energy says carefully positioned trees, shrubs or vines can save up to 25% of the energy a typical household uses.
“Adding landscaping that increases shade throughout your yard creates a cooler microclimate,” says Direct Energy, an electric provider. “This reduces your home’s cooling load and helps reduce local air temperature for your condenser.”
Window A/C units work differently.
Their design makes it less likely shading can restrict the unit’s airflow, and according to Direct Energy, direct sunlight on a window unit can reduce its efficiency by up to 10%.