# What is the maximum angle I can set my window AC unit?

We know an AC unit must be angled to allow runoff. But what is the maximum angle and what is the issue with having to large of an angle? I've seen people say the angle is "5/16" or "3/16" but this is nonsense as an angle is not a length.

I am installing a window unit and would like to try and get the optimal angle if there is one.

• When talking about gradient, angles are expressed as lengths. As in 1/4" per yard or 5/16" per foot. In rafters and stairs, this is called rise and run. It's sensible and much easier to figure than getting a protractor, a piece of string and monkeying around with a swinging weight to figure angle. It's also what that surveyor's helper is doing with the grade stick. The transit is viewing an absolute level and the number at the target is the +- grade from the marker. Commented Aug 17, 2013 at 5:40
• @FiascoLabs Ok, but that isn't the angle.... If someone says it's 5/16 how do you know it's per yard, foot, inch, meter, grape, or apple? Commented Aug 17, 2013 at 5:56
• @user14448: It is 5/16 over the whole the depth (inside to outside length) of the air conditioner. Commented Aug 17, 2013 at 7:56
• FiascoLabs makes a good point - if it's 5/16 over the depth, that's not a set angle, the angle is variable. 5/16 over 1' vs. 5/16 over 10' is very different indeed. Commented Aug 17, 2013 at 12:07
• As with all manufactured product, the installation instructions are pertinent to the make/model you're installing and are what the manufacturer recommends. What does the manual say? In this case, the rise is given and the base measurement for the run (equivalent to our foot or yard for other applications) is either the length of the case or from where the unit rests on the window sill and is determined by the manufacturer as they know what the internal structure needs. They are giving you the optimal angle in a manner that you can verify. Commented Aug 17, 2013 at 16:56