An Easy Way to Save Money — Let Your Air Conditioner Breathe!

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hvac air conditioner heat transfer condensing unit air flow plants

Here's an easy thing you can do to keep your air conditioner running as efficiently as possible: Don't crowd the condensing unit, the outdoor part of your AC. In the photo at left, you see a common problem. I took this picture at a brand new house a couple of months ago, and there's not a problem right now, but what's going to happen to those shrubs planted around the condenser?

Yep. As the shrubbery gets bigger, it's going to crowd that condensing unit. When it does, it's going to restrict the air flow across the condensing coil. Remember the articles I wrote about the refrigeration cycle — part 1, in plain English and part 2, in a bit more technical language? If not, now might be a good time to go read them.

Basically, the condensing coil is where all the heat that got picked up from your home gets dumped outside. Your AC is engineered to remove the heat by having a designed amount of air flow over the condensing coil. If less air flows over the coil, less heat is removed. That means the whole cycle warms up a bit, and your AC works harder to keep your home cool.

You'll pay extra for it in more than one way: (i) Your monthly electric bill will be higher; (ii) your equipment may not last as long, so you'll pay more in repair bills and in having to replace the AC sooner.

There are a lot of ways that condensing units get their air flow blocked. The most common is from plants growing too close to the unit, as shown above. Dirt and leaves piling up around the condenser cut air flow, too. These are things you can easily control by trimming the plants around the condenser and clearing away any debris.

If enough dirt gets between the fins of the condensing unit, that's also going to reduce air flow. When you get your HVAC system serviced each year (you do, don't you?), the service tech should check and clean the coil if necessary.

Sometimes, the HVAC company creates the problem. The photo below shows one such case.

hvac air conditioner condensing unit too close bad airflow energy efficiency

Not only are those condensing units too close to the wall of the house and the fence, they're way too close to each other, too. They're going to be fighting each other for air when adjacent units are running at the same time. This is a terrible installation and should never have passed the building inspection.

So, keep some space around your condenser and let your air conditioner breathe!

 

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Comments

ryan
Jul 29 2011 - 6:42am

Great points, there is often the issue of plants growing over the top the units or even worse the units have been placed under the structure ie porch roof, cantilevered section, or people have built something over them to "hide" them, all bad ideas. Keep up the good work.

Allison Bailes
Jul 29 2011 - 7:04am

Ryan: Thanks. The photo at the bottom of the article is the result of someone trying to hide the condensers. Hiding them isn't bad in itself. I don't like these things either, but at least give them space inside their hiding place, people!

Josh
Jul 29 2011 - 8:45am

What is the recommended clearance around the units to maximize the air flow?

Allison Bailes
Jul 29 2011 - 10:53am

Josh: Probably every manufacture has a different recommendation, but I'd think you definitely shouldn't have anything closer than 12" on the sides and probably 4 feet or so on the top. Two to three feet on the sides would be even better.

Matthew Klein
Jul 29 2011 - 10:57am

I also had questions about how much clearance. I was able to find a few installation instructions on-line that did not fully clarify the issue. Carrier calls for 3 foot on one side and 1 on the other--does that mean an average of 2? I am thinking 2 should be enough. 
 
More important, though, was the clearance ABOVE the unit. Carrier states clearly 60 inches. I am thinking that clearance above the unit is more important than around it because that is the business end of the condenser air flow--the fan. 
 
The other issue I would love to see discussed about condensers is location. Why in multistory buildings with individual AC units are the condensers placed on the hottest part of the building--the roof. These buildings usually have parking areas and, as anyone who has walked past one of the open garage doors on a hot summer day, that air is pretty cool.

Allison Bailes
Jul 29 2011 - 11:20am

Matthew K.: Great points. I think the reason you see different clearances for different sides has to do with how much of the condensing coil is on that side. They also probably design the unit so that one side can be close to the house and they can still get enough total air flow. 
 
Regarding top vs. sides, they're both the 'business ends' actually. All that air blowing out the top had to be sucked in through the sides. The reason you need more clearance on the top is that you have more air moving through a smaller area there. 
 
Placement of the condenser is also an interesting issue and deserves its own article. I'll mention one other neat thing that you can do, though, and that is to mist water onto the condenser to help cool it even more. You get a little bump in efficiency when you do that.

David Butler
Jul 29 2011 - 12:18pm

Given a condenser room to breath is indeed critical, but I think setting the actual clearances is more art than science. Take a look at the instruction for my unit: 
 
"A service clearance of 30" must be maintained on the side adjacent to the control box. Clearance to one of the other three sides must be 36". Clearance to one of the 
remaining two sides may be 12" and the final side may be 6". 
 
"A clearance of 24" must be maintained between two units. 48" clearance is required above the unit. Maximum soffit overhang is 36"." 
 
 
I don't care what the book says, I would never accept 12" on one side, let alone 6"!

Steve Zimko
Jul 30 2011 - 7:15am

Does shading the condensing unit help? If adequate clearances are provided around the unit, will shade from a fence or shrubs improve efficiency?

John Brooks
Jul 30 2011 - 10:53pm

According to FSEC 
 
http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-302-96/ 
 
"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." 
 

Steve
Mar 13 2012 - 4:32pm

You could just pull out those shrubs and get a tricc utility cover. I am a general contractor, and I use them all the time on my jobs. The thing will make it seem as if the unit isn't even there. Great innovation. Otherwise, I love the article. You made some very valid points. I wish every home owner was aware of the problems you brought up. When I do a job for someone who wants to plant around a unit I always try to warn them of the danger. Now I don't have to worry about it, because I use those tricc covers. My customers love it.

stan
Aug 27 2012 - 7:04pm

Great discussion! 
 
I have two 3-ton heat pumps that are beneath an eave that extends out 30 inches. But the units are about 15 inches from the house, so that the overhang is only about 15 inches over the units. The opposite side of the units are almost 2 foot from a block wall. The units are 4 feet apart and they are 4.5 feet beneath the eave. Nevertheless, exhausted heat from the condensor seems to recycle down from under the eave where hot air collects. 
 
I currently have a big fan blowing away hot air from under the eave. It helps, as discharge pressures come down. 
 
I need a permanent solution. AC guys talk about deflectors attached to the side of the unit which divert the air away from eave area. This, however, is not so easy, as the units are curved at the top. 
 
Has anyone tried to cut a hole in an eave and put a simple exhaust fan? (power could come from one terminal of the contactor, etc). When the fan comes on, it would suck any hot air out from beneath the eave.

Dave
Jan 29 2014 - 8:16am

We have two heat pumps at the back of the house. We have large overhangs that are about 15 feet above the units. The room they are next to is always cooler or warmer. Could the air discharge from the two units be hitting the windows and causing the room to be cooler or warmer because of the overhangs?  

Suzanne Tiemstra
Mar 3 2014 - 12:42pm

I have one of those new 5 foot tall X 30" on each side condenser units. It's huge! How can I work it into my landscaping? It's squeezed in between my patio, house, and walk. I painted my previous smaller condenser with dark green heat-resistant Rustoleum and it worked out great. Can I do that with this one, too? I don't want a huge fence, and there is not enough room to grow anything tall in front of it.

David Butler
Mar 3 2014 - 1:08pm

@Suzanne, it's ok to paint the cover plates but do not under any circumstances paint the coil itself. That would pretty much ruin your day.  
 
Sounds like your unit was located in a bad place. You might want to consider relocating the unit. The refrigerant lines would likely need to be re-routed instead of extended since there's a limit to the line length.

Suzanne Tiemstra
Mar 3 2014 - 7:31pm

Thanks, David. It's nice to get a quick response! Would it be ok to put window-screen-like panels around it? I saw that done on a web site.

David Butler
Mar 3 2014 - 11:59pm

@Suzanne, there's no way to predict. You'd have to have an HVAC tech check the head pressure with and without the screen to know for sure. 
 
@Stan, 4.5' overhang clearance may be within mfr spec, but with two units (even widely spaced as you indicated), I'm not surprised it's causing enough feedback to affect heat pressures a bit. But installing a fan in the overhang is a lame idea, IMHO. If you're willing to cut a big hole in the overhang, you'd be better off just removing a few feet of the overhang and reworking the frieze detail. 
 
@Dave, an overhang at 15 feet will have little if any affect on the exhaust air, but if either unit is directly under a window, it wouldn't surprise me if exhaust increases that window's heat gain/loss. 
 
Putting a condenser under a window is dumb, if just for noise transmission. If that's the case, you should consider having the offending condenser moved away from the window. On the other hand, if neither unit is under a window, I seriously doubt there's enough feedback from an overhang that high to affect your windows.

Robin Nordhoff
Jul 22 2014 - 12:20am

I am interested in finding out if I can place the outdoor part of a/c unit behind my detached garage instead of the house. The distance would be about 20'. Would any type of lines or electrical need to be run. The house is located in Northern Idaho.

David Butler
Jul 22 2014 - 1:53pm

@Robin, a licensed HVAC contractor needs to advise you on this. The distance may or may not be an issue, depending on how long the existing refrigerant lines are (the copper tubes that connect the outdoor unit to the indoor unit).  
 
Moving a condenser requires evacuating and recovering the refrigerant and field-splicing additional copper tubing to the new location. The electric disconnect switch would also need to be moved or extended.  
 
Each manufacturer has different limits on how long the refrigerant lines can be. Depending on the design of your home, it may be possible to re-route the refrigerant lines in a more direct route, rather than simply extend them.