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Placement of air conditioner condenser unit : roof or ground?

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Joined: Feb 26 2018

I recently purchased an Eichler in San Mateo.  I have to do a lot of work to it -- electrical, plumbing, foam roofing.  And, I'm planning on putting in an air conditioner.  Ducting already exists.  I've seen AC condenser units on roofs, but I know traditionally they are installed on the ground.  Are there any downsides to placing the AC condenser on the roof?  I know it will be harder to know whether there is an issue with it because I won't be able to see it readily.  

I have a sloped roof in the front of the house and a flat roof in the back (where the bedrooms and bathrooms are).  I was thinking of placing the unit on the flat roof part of the house , above the bathrooms which are adjacent to each other.  


Any feedback on your experience would be helpful.



Joined: Apr 19 2007

I've seen them on both the roof and groud as well ... we have ours on the roof.

On the ground: You need to make way for the lines to get up /to/ the roof to reach the rooms — this is generally done by runnning the lines up the wall and encasing in a chase (or box)... this plus the condensor and wiring are sometimes unsightly if not downright ugly, especially if the lines are run along the house versus up/over the roof.

On the roof: You don't need to worry about the lines as they are spread out on the roof. You have one main electrical conduit coming up from the panel to supply power, but otherwise, little on the ground. However, the unit /does/ produce a percussive vibration that is akin to fingers on a drumm skin (and you in the drum), so place the unit over an uninhabited place like a shower or closet (ours is over the master shower... honestly by chance). If placed over a bedroom, you /will/ hear it.
In both cases, if the lines go over the roof, it seems to be best done /before/ a foam roof is sprayed on (and the foam goes over the lines). With the number of penetrations in the roof, sealing up /without/ foaming over might actually be tough and I've known folks that attempted to do this experience leaks afterwards.

In the end, a /lot/ of planning goes a long way — especially when considered in context with other projects (like an electrical upgrade, a new roof, etc.)

Joined: Feb 26 2018

Thank you for your comment.  It was very helpful!
I decided to place my A/C on the roof and will have my roof foamed over.  My HVAC contractor suggested placing the A/C unit above where a major beam is so there is sufficient support for the unit.  I have to confirm that this isn't going to be near a bedroom.

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