I live in a warm, humid, coastal town and when my air conditioning runs it creates condensation in some areas. This week I noticed rust on the wallpaper under one of my sconces and when I open it up, the mounting screws were badly rusted and the interior of the sconce was very wet. The junction box in the wall smells damp and mildewy.

It's possible that the water is coming from somewhere else, but the junction box itself seems dry. E.g. there's dry drywall dust inside it.

How should I address this?

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2 Answers 2


Moist air is making its way into the electric box, then it condenses when it hits the metal cover plate (which is cooler than the inside of the box, since it's in contact with the air-conditioned inside air). This probably means that your house's weatherproofing (insulation, vapor barrier, etc) is lacking. So the long-term solution is to weatherproof the house, but that's a pretty big project. If you want something quicker: get a piece of closed-cell insulating wrap, like pipe insulation, and use that to cover the metal plate that's attached to the wall and to block the hole, then put the metal cover back on.

  • 1
    Another thing to check: if your bathroom has an exhaust fan, make sure it's vented to the outside. Venting it into a crawlspace or a wall cavity is totally wrong, and a lot of people do it anyway. Aug 5, 2023 at 14:01

The air in your home should be low in humidity if the AC is working correctly.

You didn't indicate what type of AC unit you have. Some of the Mini-Splits can be oversized for a room and cool too quickly without removing the humidity.

You will need to look at sealing the electric box to prevent outside humid air from entering. ( This should be done in any case, regardless of the type of AC)

Turn off power to the light at the breaker. Remove the mounting plate. If the openings are small, seal the area around the box with caulk or foam.

Examine the area and inside the box. Look for areas where it is open to allow outside air in. Depending on what you find, you may want to post another question with pics of what you see, to get advice on how to seal and insulate the area.

  • Seal and/or insulate the box.
    – Huesmann
    Aug 5, 2023 at 14:40
  • 'good stuff', which is horrible for the environment, but better than taxing your AC.
    – Mazura
    Aug 5, 2023 at 17:35

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