Why Bathrooms Stay Humid No Matter the Fan

(What’s Really Going On in South Louisiana Homes)

If your bathroom stays humid even when the fan is running, you’re not alone.

A lot of South Louisiana homeowners deal with:

• mirrors staying fogged forever

• walls feeling damp

• towels that never fully dry

• mildew showing up quickly

• paint peeling near the ceiling

• musty smells that keep returning

And you might think:

“But the fan is on… why isn’t it working?”

Here’s the truth:✅ Many bathroom fans are not actually removing moisture the way people assume.

Let’s break down the real reasons and what fixes them.

Why Bathroom Humidity Is a Big Deal in Louisiana

Bathrooms are already high-moisture areas, but in South Louisiana:

• the outdoor air is humid

• homes hold moisture longer

• AC systems sometimes don’t dehumidify enough

• moisture problems show up faster

So if a bathroom doesn’t vent properly, the humidity hangs around and turns into:

• mold

• peeling paint

• caulk failure

• warped trim

• long-term hidden damage

The #1 Reason: The Fan Doesn’t Vent Outside

This is the biggest problem we see.

A bathroom fan needs to vent to:✅ the exterior of the home (roof cap or wall vent)

But many fans:

• vent into the attic

• vent into soffits incorrectly

• dump into an open cavity

• have disconnected ducting

• blow into flexible duct that’s crushed

If it’s not venting outside, it’s basically just spinning humid air around.

✅ Clue:If you go in the attic and see a loose duct near the fan, that’s a major red flag.

Reason #2: The Fan Is Too Small for the Bathroom

Fans are sized by CFM (cubic feet per minute).

Many builders put in basic fans that aren’t strong enough.

If the fan is undersized:

• humidity will rise faster than the fan can remove it

• steam sticks to ceilings and corners

• mold returns quickly even after cleaning

✅ Clue:You can run it for 30 minutes and still feel humidity.

Reason #3: The Duct Run Is Too Long (Or Too Restrictive)

Even a good fan won’t work well if the ducting is wrong.

Common issues:

• long duct runs with too many bends

• duct too small

• crushed flex duct

• duct sagging and holding water

• duct disconnected at the vent cap

Moist air needs an easy path out.

✅ Clue:The fan sounds loud but doesn’t seem to “pull” humidity out.

Reason #4: The Fan Is Dirty or Worn Out

Over time, fans clog with:

• dust

• lint

• humidity residue

A dirty fan moves much less air.

✅ Clue:The fan cover is dusty or the suction feels weak.

Sometimes cleaning helps.Sometimes replacing the unit is the best fix.

Reason #5: You’re Not Running It Long Enough

Most people turn the fan off the second they step out.

In Louisiana, that’s usually not enough.

A better rule:✅ Run fan during shower✅ Keep it running 20–30 minutes after

Why?Because moisture stays on surfaces and keeps evaporating into the air after you’re done.

Reason #6: Your Bathroom Is Pulling Humid Air From Somewhere Else

This is common in older homes.

Humidity can enter a bathroom from:

• air leaks in walls or ceilings

• attic air leaking down

• crawl space moisture rising up

• exterior wall penetrations

• leaky windows

So even if you vent some moisture out, more moisture keeps coming in.

✅ Clue:Bathroom always feels “damp” even when no one showers.

Reason #7: The House Humidity Is High Overall

Sometimes the bathroom is telling you something bigger:

Your whole house humidity might be too high.

If indoor humidity stays above:⚠️ 60%, bathrooms struggle to dry out.

That’s when you may see:

• musty smell

• sticky feeling inside

• mold returning in multiple places (not just bathroom)

✅ Fix may involve HVAC airflow and dehumidification, not just the fan.

Reason #8: Moisture Is Trapped Behind Walls or Tile

If humidity problems have gone on for a long time, moisture can live where you can’t see it:

• behind tile

• behind shower walls

• under a tub

• under flooring

• behind baseboards

Even after you “dry the bathroom,” the trapped moisture keeps feeding humidity and odor.

✅ Clue:Recurring musty smell even after cleaning, or soft spots near the tub.

What NOT to Do

These common moves waste money or make it worse:

❌ Painting over humidity stains without fixing ventilation

The stain comes back.

❌ Caulking everything repeatedly

Caulk fails again if moisture is constant.

❌ Using a cheap fan as the only solution

If ducting is wrong, the fan won’t matter.

❌ Ignoring it because “it’s Louisiana”

Bathrooms shouldn’t stay wet for hours every day.

What Actually Fixes a Humid Bathroom

Here are the real fixes that work long-term:

✅ Vent the fan to the exterior properly✅ Use correct fan size (CFM) for the space✅ Shorten and straighten duct run when possible✅ Replace weak or worn fans✅ Seal leaks from attic/crawl space into the bathroom✅ Keep humidity down throughout the home✅ Use moisture-resistant materials during remodels

A bathroom should:

• clear steam reasonably fast

• dry towels normally

• stay clean longer

• stop feeding mold growth

Why This Matters Before a Bathroom Remodel

If your bathroom stays humid now and you remodel without fixing it:

• mold returns faster

• paint peels on new work

• caulk cracks early

• woodwork swells

• long-term damage can build behind finishes

A remodel should solve the problem, not dress it up.

Need Help Solving It the Right Way?

At Cajun Conservation, we build and remodel bathrooms across South Louisiana with a focus on:

• proper moisture control

• durability in our climate

• craftsmanship that lasts

Question for you:When your fan runs, does the bathroom steam clear within 10–15 minutes, or does it stay humid for 30+ minutes?