Best Humidity level indoors?

11 years ago

I recently moved to southern Florida, where dry winter air isn't a problem, it's just the opposite. We like to open doors and windows on nice days, but realized even on cool clear days, it can be very humid. One morning we opened the bedroom closets and discovered all our clothes covered in mildew. I bought a de-humidifier and two humidistats, one for outside, one for inside. I'm just not sure what a safe humidity level is to prevent mold and mildew. I turn the de-humidifier on when I notice the indoor humidity above 70%, but aren't sure if it should be less than that, or if that may be dryer than necessary. Needless to say, I haven't opened any windows since putting a humidistat outside (on the porch), the humidity is always way over 70%, and often in the 90's even though it seems to be a clear dry day.

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Comments (8)

tigerdunes
11 years ago
For your location, no higher than 40 RH year round...

IMO
energy_rater_la
11 years ago
50% is my goal in hot humid La.
while you are on the right track with the stand alone
dehumidifiers, a whole house dehumidifier would
be something to consider.

do you have hvac supply vents in closets?
we pretty much have to do that also, especially
if closets are in master bath.

I love to open windows also when temps are
cool. but then when it gets hot..the a/c goes on
& during the shoulder seasons & I run the whole
house dehumidifier. (shoulder seasons...spring/fall).

air sealing the house, mastic sealing the ductwork
also helps. when sealing ductwork...don't forget
the return air.

best of luck.
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echobelly
Original Author
11 years ago
@energy_rater_la

All the closets are vented. It's an older house (1945) and one contractor mentioned there may not be a moisture barrier under the slab. We just had a new AC system put in, and I asked if there was a system that would de-humidify only, without cooling. The AC contractor said no, I didn't question it. I did just speak to someone who has a whole house de-humidifier, and they said they keep it set to 80%. That seems pretty high to me.
energy_rater_la
11 years ago
80% is too high. mold & dust mites are kept inactive @ 50% RH.

no vapor barrier under slab would show up quickly.
what kind of flooring do you have?
hard to believe that the slab would have passed
code inspection.

did you get a system with dehumidifying mode?
what did you get, brand & size.
how big is the house.
what type construction.
where is ductwork located.
mike_home
11 years ago
"the humidity is always way over 70%, and often in the 90's even though it seems to be a clear dry day."

Is the indoor humidity higher that that of the outdoor? If so then you must have a source of indoor moisture that needs to be addressed.
energy_rater_la
11 years ago
same here in La. summertime sunny day...80% humidity.
in my house I can easily lower RH to 40%.

when I lived in N.O. tourists would ask how can it
be 100% humidity & no rain.
the answer...wait until 3 pm.
nothing like a steamy summer afternoon...LOL!
echobelly
Original Author
11 years ago
Doesn't look like I"ll be opening windows anymore :( Granted, I've only had a humidistat for a month, but this is the driest time of the year and it rarely gets below 75%RH.
ionized_gw
11 years ago
Here are some reports that might interest you:

http://www.buildingscience.com/documents/bareports/ba-0214-conditioning-air-in-the-humid-south-creating-comfort-and-controlling-cost

http://www.buildingscience.com/documents/bareports/ba-0505-residential-dehumidification-systems-research-for-hot-humid-climates