Do I Need to AC My Bedroom During the Day to Prevent Mold?

July 11, 2023 11:22 PM

I formerly lived in a hot dry city, and in the summer I would close all the doors to all the rooms during the peak hours and only AC my living/ dining room. I now live in a hot humid city, and am wondering if not keeping my bedroom cool/ dry (I'm running my AC in dehumidifier mode) during the day will invite mold. I don't want to needlessly cool a room I'm not using, but I don't want ruined bed and/ or closet stuff either, so bedroom door: open or closed during the day?
posted by my log does not judge to Home & Garden (7 answers total)

Open. Don't think of it as needlessly cooling a room you're not using, thinking of it as pre-emptively saving yourself thousands of dollars in mold rememediation and re-purchasing ruined belongings.
posted by CheeseLouise at 11:46 PM on July 11, 2023 [7 favorites]

Open. If you're trying to save money, you can close the bedroom vents during the day, but it will likely take a while to cool at night for bed, and that could be annoying.

I live in a hot humid city and previously closed the vents for my guest room/ office when it wasn't heavily in use, as well as closed the door to keep my cats out. I have central air and have not experienced mold issues.
posted by wicked_sassy at 6:25 AM on July 12, 2023

Even if you don't have a mold threat a closed, unventilated room in a hot/humid climate will begin to smell really musty. Keep the air moving!
posted by JoeZydeco at 6:37 AM on July 12, 2023 [2 favorites]

Another vote for open. Any cost savings you are expecting are probably minimal. Your AC should have been sized for the cooling load of your entire house/apartment. If it's effectively trying try cool a smaller space it will cycle on and off more often. Cycling on uses a lot of energy.
posted by AndrewInDC at 6:44 AM on July 12, 2023 [2 favorites]

Unless you have had your AC system rigorously and recently tested (or your electric bill is really cheap), you should almost never fully close your vents. The duct runs connecting to your AC often have small leaks, and closing vents exacerbates them. If your AC is in your attic or basement, you are adding cooling there.

If you want to close vents, you should have dampers installed, which are really close to your AC and able to close off entire AC ducting runs.
posted by The_Vegetables at 7:09 AM on July 12, 2023

Air flow is important within the room even if you leave the door open. If you can, pull furniture (especially anything against an external wall) out 4-6 inches.
posted by lovableiago at 10:17 AM on July 12, 2023

I have always lived in a humid warm place and I only turn the AC on if it's consistently above 90F and humidity above 60%. Like, for days on end. Which does sometimes happen, and one particularly rainy summer I did find mold on my wooden furniture, which was easily dealt with. But generally that doesn't happen and airflow is very important. Also, to be honest, keeping your amount of stuff to a minimum so you can keep it clean also helps.
posted by epanalepsis at 10:34 AM on July 14, 2023