I got a question this weekend that's often asked—and, I'm sure, wondered about—by homeowners: "Will my household AC system run more efficiently (perhaps cycle on/off fewer times, or the compressor won't have to run as long when it cycles on) by shading the compressor?" I've written about the outdoor unit of air conditioners and heat pumps a few times, but I've never tackled this question directly. Let's change that now. First, a little explanation about air conditioners. That metal noisemaker that sits out in back or on the side of your house is called the condensing unit for air conditioners. The compressor is one component in that box, but the condensing coil and a few other parts are there, too. (To understand how an air conditioner works, see my article, The Magic of Cold.) The condensing coil's job is to dump the heat picked up inside the home to the outdoor air. (If you have a ground source heat pump, that heat gets dumped into the ground rather than the air, and you won't have an outdoor unit like the one shown above.)

The hotter it is outdoors, the harder it is to dump that heat and the more you'll spend keeping your house cool. Hence the question, can shading your air conditioner's outdoor unit provide significant savings? And the answer is yes and no. It depends on what type of shading we're talking about, but for the type of shading most people are thinking about when they ask that question, the answer is no. Shading the outdoor unit with a structure as shown below will reduce the direct solar gain from insolation but won't do a whole lot for the air temperature around the unit. That photo is from a study done the Forida Solar Energy Center on the effectiveness of shading air conditioner condensing units. Caution: The unit below exhausts from the side so the shading structure doesn't interrupt the air flow. Most AC outdoor units exhaust from the top and that structure would reduce the air flow and perhaps cause serious damage to the unit. Don't try something like this unless you have a good understanding of air conditioners.

In the Discussion section at the end of their report, the FSEC authors give the big reason why small scale shading like this doesn't work. does hvac unit workThe temperature of the surrounding air has a much bigger effect on cooling efficiency than direct solar gain, and the volume of air pulled in by an air conditioner is huge.samsung window air conditioner reviews A typical 3 ton air conditioner condensing unit might pull in 2800 cubic feet per minute (cfm) of outdoor air. cost of a new heating and air conditioning unitIf it ran continuously for an hour, 168,000 cubic feet of outdoor air would move through the outdoor unit. Since your air conditioner is probably oversized, it won't run the full 60 minutes. My oversized AC, for example, runs about 30 minutes an hour at design conditions.

Even at 30 minutes per hour, though, the outdor unit pulls in 84,000 cubic feet of outdoor air. To put those numbers in perspective, 84,000 cubic feet is about three times the volume of a typical house being cooled by that 3 ton AC. It would take a lot of shading to cool that much air. The FSEC study sums it up this way: We conclude that any savings produced by localized AC condenser shading are quite modest (<3%) and that the risk of interrupting air flow to the condenser may outweigh shading considerations. The preferred strategy may be a long-term one: locating AC condensers 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. A related question to shading the condensing unit is about saving money by spraying a mist of water on the unit, especially with the recent launch of the Mistbox. I wrote about that topic a couple of weeks ago, and again, the answer is that you're better off looking elsewhere.

If you really want to improve the efficiency of your air conditioner, your opportunites are much greater if you look to your duct system. By fixing disconnected ducts, flacid flex, uninsulated boots, and more, you may be able to cut your air conditioning bill in half, depending on how bad your particular ducts are. And they most likely are bad. 9 Uncommon Tips for Keeping Cool with a Struggling Air Conditioner Does a Heat Pump or Air Conditioner Condenser Need to Go Outdoors? An Easy Way to Save Money — Let Your Air Conditioner Breathe!I'm an Air Conditioner Compressor Killer Is Evaporative Cooling the Answer to High Air Conditioning Costs? Top photo by Energy Vanguard. Bottom photo from Florida Solar Energy Center's air conditioner shading study.Your comment will not appear below until approved.How do you move an air conditioner? Commercial air conditioners and central air conditioning units should only be moved by a licensed air conditioner repair firm that can safely disconnect coolant lines.

Air conditioners contain coolant that can be harmful if allowed to leak out. What are the different types of air conditioning units? What are the ratings for Goodman HVACs? What Dandy air conditioners are energy star qualified? Angie's List or your local Yellow Pages should have listings of licensed and bonded air conditioner repair companies. Portable window unit air conditioners just need to be unplugged and pulled out of the window before being moved to another window. Air conditioners should remain upright when they are moved. Large window unit air conditioners require several people to move, possibly with a hand truck. Take care to not damage the condenser coils. Never grab an air conditioner by the condenser coils or lay it down so that the coils can be smashed. If you are moving to a different home and want to take your air conditioner with you, then make sure to remove the filter and pack it well in a box padded with old newspaper or bubble wrap. Most people do not move a central air conditioning unit once it is installed, since a technician must do this.

Usually, outdoor AC units are only moved if a home expansion or renovation requires it. What are some highly-rated whisper-quiet air conditioners according to experts? Consumer Reports ranks the GE AEM05LS, the LG LW8014ER and the LG LW1214ER among the top room air conditioners on the market as of 2015; What is a Robinair air conditioner? As of 2015, Robinair produces air conditioner servicing equipment rather than air conditioners. The company has two product divisions: one for automotive a... What are the benefits of outside air conditioners? Outside air conditioners provide cooling throughout the home, use existing furnace duct work, do not take up window or floor space, and are more efficient ... What size air conditioners does Trane sell besides 2-ton? Trane sells 13 lines of air conditioners in various sizes besides two-ton models, which have an equivalent capacity of 24,000 British thermal units. What are the advantages of programmable thermostats?