Air Conditioner Humidity & you

Do you ever feel like your house is humid during the summer months with the air conditioner running? If you’re wondering why that matters or how they are connected, then let’s dig in! Air conditioner humidity plays a major role, as we will see here, in the efficiency, comfort, and longevity of the HVAC system.

One of the basic operating procedures of an air conditioner is to remove humidity. Why? Because moist air holds more heat. Remember those laws of thermodynamics from your high school science classes? This is why 70 degrees in Florida feels a lot worse than 80 degrees in Boise Idaho. So, if we can get the air conditioner to remove all the humidity during operation, or at least the majority of it, then your air conditioner will be running smoothly and happily. So will you and everyone in your home.

Consider this definition of “air conditioning”:

Created in 1908 and is credited to G. B. Wilson. It is the definition that Willis Carrier, the “father of air conditioning” subscribed to:

  • Maintain suitable humidity in all parts of a building
  • Free the air from excessive humidity during certain seasons

Pro Tip: Humidity from your air conditioner, if left alone, can begin causing mold growth throughout your home and ductwork system.

How is humidity created by my air conditioner?

As air passes over the evaporator coil (usually located below or above the furnace) it condenses as it cools from the freon passing through the refrigeration lines. As air condenses across these coils, the moisture is wrung out just like when you squeeze a sponge. The perfect recipe for air conditioner humidity.

A few common signs of high indoor humidity include:

  • Moist, clammy air. Your skin may feel more clammy when you’re inside your home.
  • Cupping wood floors. Wood is like a sponge and will soak up a lot of humidity in your house.
  • Foggy windows. This happens because the humidity is vaporized water in the air. When it becomes bottled up in your home, it may fog up the windows.
  • Musty odors. Excessive humidity causes dampness throughout the home and can eventually lead to unpleasant smells; even when the air conditioner is off!

Time for a history lesson

Some older evaporator coils were added into homes where heating was the only comfort. Many homes used to not have air conditioners from the ’50s to the late ’70s! So contractors would come in and simply try to add in cooling with minimal cost involved. Heating requires a lot less airflow, naturally, than air conditioning so adding air conditioning would require redesigning ductwork and supply and returns for the system to operate at its best efficiency possible. But, as the market and industry were new to air conditioning, most contractors were simply unaware of the needs required to pull off this new modern marvel. Looking back now, our industry laughs at how many hacks jobs were installed. As the industry became more aware and more educated and more science and data were collected, contractors began offering the redesigning of the ductwork as a necessity for retrofitting an air conditioner into an existing home. This also required education for our customers to warrant the additional costs needed to make this happen. Imagine one contractor seems to think it’ll be an easy-peasy job to hook up air conditioning to your existing home and another is talking about redesigning ductwork and plenums and CFM’s and volumes… All while the homeowner may be thinking “Is this the system they use in NASA?”

So, let’s fast forward to the 90s when residential home construction began skyrocketing across the nation, and builders, along with homeowners, began having room in their profits to demand better homes and better air conditioner systems. Air conditioning became a requirement for new houses. Who would even look at a home without air conditioning?? With this requirement came a new set of standards that many entities across the building industry and trades tried to enforce and oversee.

Let’s fast forward to the 21st century. Now we have manufacturers that can build equipment that takes into consideration the effect of humidity on your air conditioner system.

Retrofitting a new air conditioner into a home that was built before 1990 will more than likely require some additional ductwork to accommodate the additional airflow needed for the air conditioner. When the ductwork is left alone, it leaves the system starving for airflow causing higher-than-normal amounts of condensation. More moisture. More humidity throughout the home. More, well you get the point. More isn’t better…

Maintaining proper humidity levels in your home

The main factors that affect air conditioner humidity:

  • Airflow and ductwork sizing
  • Equipment sizing according to the needs of the home- square footage, windows, insulation values, etc.
  • The envelope of the home- vapor barrier in the crawlspace, amount and type of insulation in the crawlspace and attic

And there are specific needs of the home that a blueprint or engineer could never see. Such as the number of people living in the home. If you work from home or not. What sort of temperatures do you like while you are at home? Some people like their temperatures at 68 during the summer months while others are comfortable at 78! What a wide range you ask? Certainly is!

Still with us?

Ok, so now you’re thinking- yep, we have all these problems.

How do we fix these issues and get back to normal?

Fixing air conditioner humidity from your evaporator coil and air conditioner system needs to first start with a thorough evaluation and diagnostic of the system, the ductwork systems, and the needs of your particular home. In my experience, the majority of contractors in the trade are not experienced enough to know how to resolve this. Do your homework and vet contractors! Find out if they have taken care of air conditioner humidity problems before and what some of these solutions have required. Don’t be afraid to watch and engage throughout the visit to learn as much as possible. Expect to pay a diagnostic fee and be prepared to look at various options for how to solve this.

A one-size-fits-all answer just would be bad information!

Pro Tip: A larger air conditioner than required for your home will cause high humidity. A properly sized system will keep your bill down and you comfortable.

But, here are some general tips for reducing your air conditioner humidity levels in your home:

  1. Forced air systems can be set up to circulate the indoor fan motor even when the air conditioner is off. Moving air after the air conditioner turns off will run air across the evaporator coil to dry and remove as much moisture as possible. Some newer systems are even designed to run the fan for 60 or 90 seconds after the air conditioner turns off to assist with a dryer evaporator coil.
  2. A larger evaporator coil. Wait, didn’t we mention earlier that larger isn’t better?? New evaporator coils are more energy efficient than their older brothers. This increase in efficiency is done simply by increasing the surface area of the coils. More surface area means less restriction which means less condensation but the same cooling capacity and BTU values. Say goodbye to air conditioner humidity!

You will certainly want to measure the air conditioner’s humidity during the summer months. Some thermostats have the capability of displaying this in real-time. If yours does not, you can purchase a weather station or a more sophisticated model that can measure the humidity from your air conditioner.

Now, most of the information here is written from our unique vantage point of being located in Boise Idaho. Since we live in the desert, we naturally have lower humidity. But, because the majority of our systems are forced air, humidity plays a big role in the design of our solutions. Other parts of the country have naturally higher humidity than we do.

We generally have to add moisture during the winter months but will often see 30%-45% relative humidity in most of our homes during the summer months.

Some climates require the installation and use of a dehumidifier to assist in lowering the humidity levels during the summer months. Talk with your contractor about the specific needs of your particular home and hear what options may be readily and easily available.

So, there you have it. The web’s most comprehensive guide on your air conditioner humidity. Well, maybe not. But I think we covered everything that’s most pertinent. Besides, we couldn’t find anything as informative as ours.

Our technicians receive weeks of training every year to bring you the solutions that meet the needs of your home and equipment, not just templates that seemed to work on the last job. Let us dry out that air conditioner humidity once and for all!

Please add your experience with air conditioner humidity in the comments below and we will do everything we can to help out and get you going in the right direction!


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