My last through-window air conditioner started smelling moldy after a year or two. Improper drainage, I guess? The instructions always say to install the air conditioner at a "slight tilt" so the water that collects will drain out the back.

But how much tilt is the right amount? My last air conditioner was tilted 2 degrees, according to a clinometer app for my phone, and it still got moldy. Should it have been 4? 5? 6?

1 Answer 1


The last window unit I installed stated 5 degree tilt but even this may not be enough in a dusty area where the dust collects and plugs the drain. I would follow the manufacturers requirement and if there are still problems unplug the unit and flush it every month or so to keep it free of buildup that can plug the drain.

  • Unfortunately, all the manufacturer says is "a slight angle". They don't specify.
    – baudot
    Commented Jun 15, 2018 at 20:21
  • Do what looks right, very slightly tilted. I believe the narrow tray at the back is supposed to be filled with condensate water to cool the bottom coil of the condenser. If you would tilt it too much, then there would be less water in that tray. Keep it level across the window frame. Commented Jun 16, 2018 at 21:36
  • 1
    Try spraying the evaporator coil with 3 % hydrogen peroxide from the pharmacy. this would kill mold without causing a smell of its own and without causing corrosion. Don't use highly concentrated hydrogen peroxide without diluting it first. Commented Jun 16, 2018 at 21:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.