Why Is My Home So Humid?

August 14, 2017

Your air conditioner actually has 2 roles: to cool and dehumidify the air in your home. So if you’re feeling sticky and sweaty in your home, chances are you’re really dealing with some kind of AC problem.

More specifically, if your home has high humidity levels, you likely have:

  1. Set your thermostat fan incorrectly

  2. A dirty air filter

  3. Low refrigerant levels

  4. A dirty evaporator coil

  5. An oversized AC

Unfortunately, you’ll only be able to fix some of these problems on your own. The others? You’ll likely need a professional to remedy.

We’ll show you what you can do to troubleshoot an AC system that isn’t dehumidifying your home. First, though, let’s let’s look at how your AC removes humidity from your home in the first place.

How your AC removes moisture from the air

Your AC relies on what’s called an evaporator coil to cool the air in your home.

What your evaporator coil looks like.

This device sits inside your home and is basically an A-shaped web of copper coils, which are filled with very cold refrigerant. As warm air from your home is pulled over the evaporator coil, the refrigerant absorbs both heat and moisture from the air.

Over time, moisture builds on the evaporator coils, drips into a condensate pan and drains away outdoors via a condensate drain line. The more moisture that drains outside, the less humidity in your home.

But sometimes, certain problems in the AC system can prevent this dehumidification process. So let’s look at how you can troubleshoot an AC system that isn’t properly dehumidifying your home.

Troubleshooting an AC that isn’t dehumidifying

1. Check your thermostat fan settings

Take a quick look at your AC thermostat. Is the fan set to ON or AUTO?

On Vs Auto Red Circle Edited

If your thermostat is set to ON, switch it to AUTO immediately.

Why?

Well, when your thermostat fan is set to ON, it runs non-stop—even when your fan isn’t cooling. So why does a fan that runs constantly cause high humidity?

Well, when your fan is blowing directly on your evaporator coils, it doesn’t allow for moisture to collect and drain away. Instead, the fan blows that moisture right back into your home. And over time, that means higher and higher indoor humidity.

The fix: Set your fan thermostat to AUTO.

2. Check for a dirty filter

A dirty air filter restricts the amount of warm, humid air your AC can “breathe” in. And the less air your AC can breathe in, the less air it can cool and dehumidify.

A dirty filter also means higher electricity bills since your AC has to run longer and work harder when it can’t breathe in as much air as it’s used to.

The fix: Change your air filter if it looks like the filter to the right (in the pic below). You may need to call in a professional if you’re having trouble locating or changing out your filter.

Dirty Vs Clean Fiberglass Air Filter2

3. Check for signs of low refrigerant

Your refrigerant is the secret force behind your AC’s ability to cool and dehumidify air. Think of refrigerant as a magnet that attracts heat and moisture in the air. So, if you’re running low on refrigerant, your AC won’t be able to extract as much moisture from your home.

Signs of low refrigerant include:

The fix: If you see the signs of low refrigerant, you have a refrigerant leak somewhere in your system and will need a professional to find the leak, repair it and then recharge your system.

For more information on low refrigerant levels read our blog“How Often Does an AC Need More Refrigerant?”.

4. Check for a dirty evaporator coil

Dirt and dust on your evaporator coils restrict how much moisture the coils can pull out from the air in your home. And over time, this leads to high indoor humidity.

A dirty, rusted evaporator coil.

The fix:Have a professional check for dirty evaporator coils. They’ll be able to inspect the coils and clean them if needed.

5. Check for signs of an oversized AC

If your air conditioner is oversized for your home, it will run in short bursts, preventing your AC from dehumidifying your home.

You see, your AC isn’t actually dehumidifying your home until there’s enough moisture on the evaporator coils to drip off and drain away outdoors. Until that happens, moisture isn’t actually exiting your home.

But it takes time for enough moisture to accumulate and exit your home. Typically, it takes about 15 minutes for a correctly-sized AC to start dehumidifying your home. And, unfortunately, air conditioners that are oversized never run that long. Instead, an oversized AC reaches your home’s set temperature very quickly then shuts off, preventing the AC from ever dehumidifying the air.

The fix: If you think your AC might be too large for your home, have a professional perform a “Manual J calculation”.

This calculation determines how much heat your home accumulates in a certain timeframe. Knowing this will help you determine what size AC unit you really need. If it’s determined that your AC is oversized, have a professional recommend the correct AC size needed and provide a quote for the AC replacement.

Related: What Size Air Conditioner Do I Need for My Florida Home?

Need help from a Tampa tech?

If you need help fixing an AC unit that isn’t properly dehumidifying your home, contact us.

We’ll send over a professional who can pinpoint and fix the problem in no time.


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