How Heat Pump Through-the-Wall Systems Handle Humidity Better Than Many Older Air Conditioners

By Jake Lawson

When homeowners tell me their room feels “cool but still sticky,” I usually know exactly where the conversation is going. Many people are surprised to learn that temperature and humidity are two separate parts of indoor comfort.

It's easy to assume that an air conditioner automatically lowers both the temperature and humidity at the same time. While air conditioning does remove moisture as part of the cooling process, simply making a room colder doesn't necessarily mean it's removing enough humidity.

A room can reach the thermostat setting and still feel damp, clammy, or uncomfortable.

I've seen this frequently with older through-the-wall air conditioners. The unit was still producing cool air, but its ability to manage indoor moisture was no longer adequate—or, in some cases, the system was never particularly effective at dehumidification to begin with.

That's an important distinction because comfort isn't determined by temperature alone.

Modern through-the-wall systems, particularly models equipped with heat pump technology, incorporate improvements in areas such as airflow management, coil design, controls, and refrigeration technology. When properly sized and installed, these features can help the system manage both temperature and moisture during normal cooling operation.

Of course, actual performance depends on the equipment, room conditions, climate, sizing, and installation. But when all those factors are properly matched, a newer system can provide a more balanced indoor environment rather than simply producing colder air.

Amana PBH093J35AA 9,300 BTU Through-the-Wall Air Conditioner with Heat Pump & Remote Control

In this article, I'll explain why humidity matters, how air conditioners remove moisture, why some older systems struggle with humidity control, and how modern heat-pump through-the-wall systems can contribute to better comfort throughout the cooling season.

💧 Why Humidity Matters Just As Much As Temperature

One of the biggest misconceptions I hear from homeowners is that indoor comfort is determined entirely by the thermostat.

It isn't.

Consider two rooms that are both maintained at 72°F (22°C). In one room, the relative humidity is around 45%. In the other, it's closer to 70%.

The temperature is identical, but most people would find the second room warmer, heavier, and considerably less comfortable.

The reason is that humidity affects how effectively our bodies can cool themselves. We naturally lose heat when moisture on our skin evaporates. When the air is already holding a lot of moisture, evaporation slows down, making us feel warmer even though the thermostat shows the same temperature.

Humidity affects much more than personal comfort.

Excess indoor moisture can contribute to:

• 💧 Condensation on windows and other cool surfaces
• 🦠 Conditions that support mold growth
• 👃 Musty odors
• 🕷️ Favorable conditions for dust mites
• 🌫️ A damp or stale feeling indoors

On the other hand, air that is excessively dry can contribute to dry skin, irritated eyes, and general discomfort, particularly during the heating season.

The U.S. Environmental Protection Agency (EPA) generally recommends keeping indoor relative humidity in the 30%–50% range to support comfortable indoor conditions and help reduce environments that can encourage mold growth.

That's why a good air-conditioning system isn't simply about making the room colder. The goal is to create a comfortable indoor environment by managing both temperature and moisture.

You can learn more from these trusted resources:

• 🌎 U.S. Environmental Protection Agency – Indoor Air Quality: https://www.epa.gov/indoor-air-quality-iaq
• 🌎 U.S. Department of Energy – Energy Saver: https://www.energy.gov/energysaver
• 🌎 ASHRAE: https://www.ashrae.org

📊 Comfortable Air vs Humid Air

One thing I've learned over the years is that homeowners rarely complain by saying, "My humidity is too high." Instead, they'll say things like:

• "The house just feels damp."
• "Everything feels sticky."
• "The AC never seems to get comfortable."
• "The room cools down, but it never feels fresh."

Those comments usually point toward humidity rather than temperature alone.

🌬️ How Air Conditioners Actually Remove Humidity

People sometimes assume that an air conditioner has a separate mechanism specifically designed to “dry” the air.

It doesn't.

Dehumidification is a natural part of the cooling process.

As warm indoor air passes across the cold evaporator coil, the refrigerant absorbs heat from the air. Because the coil surface is colder than the surrounding air, moisture in that air can condense on the coil—much like water droplets forming on the outside of a cold glass on a hot, humid day.

That moisture collects as condensate and is directed out of the unit through the appropriate drainage system. At the same time, the air leaving the coil is cooler and typically contains less moisture.

In other words, a properly operating air conditioner can remove both heat and moisture as part of the same cooling cycle.

How much moisture the system removes depends on several factors, including:

• 💧 Indoor humidity
• 🌡️ Outdoor temperature and conditions
• 🌀 Airflow across the evaporator coil
• ❄️ Evaporator coil temperature
• ⚙️ Equipment design and controls
• 🏠 Room size and building conditions
• ⏱️ Cooling-cycle duration

This is one reason proper equipment selection and installation matter so much.

If the unit is oversized and satisfies the thermostat very quickly, cooling cycles may be too short for effective moisture removal. If airflow is restricted, the system may not operate under the conditions it was designed for. And if condensate drainage isn't properly installed, the moisture removed from the air has nowhere to go safely.

Good humidity control isn't a separate feature bolted onto an air conditioner. It's a result of the entire cooling system working together properly.

❄️ Why Many Older Through-the-Wall Air Conditioners Struggle

One question homeowners ask me quite often is:

“If air conditioners have always removed moisture, why do newer systems often seem to feel so much more comfortable?”

The answer isn't that older equipment was incapable of removing humidity. Many older systems simply weren't as effective or consistent at managing moisture as newer equipment can be.

And as equipment ages, several factors can gradually reduce its performance.

A neglected air filter can restrict airflow. Dust and debris can accumulate on the evaporator coil. Fan motors and other components can lose efficiency. Refrigerant-related problems can affect cooling performance. Older control systems may also provide less precise temperature management, resulting in different cycling patterns than those found in newer equipment.

But age and maintenance aren't the whole story. Technology has improved, too.

HVAC manufacturers have continued to refine:

• ❄️ Evaporator and condenser coil designs
• 🌀 Blower and fan performance
• 🎛️ Electronic controls
• 🌡️ Temperature and system monitoring
• 🔄 Refrigeration-cycle management
• ⚡ Overall energy efficiency

These improvements can help newer equipment achieve a better balance between temperature reduction and moisture removal, rather than simply making the air colder.

I've replaced many older through-the-wall units where homeowners noticed a difference in the room almost immediately after installation. They'll often tell me that the space “feels fresher” or “feels more comfortable.”

The thermostat setting may not have changed much at all.

What changed was how effectively the new equipment was managing the indoor environment.

Of course, newer equipment isn't automatically better in every situation. Proper sizing, installation, airflow, maintenance, and operating conditions still matter enormously.

But when those factors are right, modern equipment can provide a noticeably more consistent combination of cooling, dehumidification, and overall comfort.

📊 Older Units vs Modern Heat Pump Systems

🔄 Heat Pump Systems Do More Than Simply Cool

For many homeowners, the words “heat pump” immediately bring winter heating to mind. That's understandable—one of the biggest advantages of a heat pump is its ability to both heat and cool a space using the same system.

What often gets overlooked is that, when operating in cooling mode, a heat pump works much like a modern air conditioner. It transfers heat out of the room, while moisture from the indoor air can condense on the cold evaporator coil and drain away.

Newer heat pump systems can also offer improvements in overall system design. Manufacturers have continued to refine compressors, electronically controlled fans, refrigerant circuits, controls, and airflow management.

Those improvements can contribute to better efficiency and more consistent indoor comfort. When replacing older equipment with a properly sized and installed modern system, homeowners may notice that the room feels more stable rather than constantly swinging between too warm, too cold, or too humid.

The goal isn't simply to make the room colder. It's to maintain a more balanced indoor environment.

💨 Better Airflow Can Mean Better Humidity Control

The evaporator coil is central to the dehumidification process, but airflow across the coil matters just as much.

If air moves too quickly across the coil, there may be less opportunity for moisture to condense. On the other hand, severely restricted airflow caused by a clogged filter or dirty coil can also interfere with proper system operation.

That's why maintaining the correct airflow is so important.

A clean filter, clean coil, properly functioning blower, and correctly designed system allow air to move across the evaporator coil under the conditions the equipment was designed for.

Good humidity control isn't about the evaporator coil alone. It's about the entire system working together—airflow, coil temperature, refrigerant circuit, controls, drainage, and equipment sizing.

Modern through-the-wall heat pump systems are generally designed with improvements in airflow management, fan technology, coil design, and system controls that can help provide more consistent cooling and dehumidification than many older systems.

But even the best-designed equipment can struggle if basic maintenance is neglected.

I've seen situations where simply replacing a severely neglected filter made a noticeable difference in indoor comfort because the system could once again move air closer to the conditions it was designed for.

Good humidity control isn't the responsibility of one component.

It's the result of the entire HVAC system working together properly—from the filter and blower to the evaporator coil, refrigeration circuit, controls, and condensate drainage.

🌿 Jake's Mid-Article Advice

When homeowners tell me their room feels damp even though the air conditioner is running, I recommend starting with a few simple checks:

• ✔ Check or replace the air filter.
• ✔ Make sure indoor and outdoor airflow isn't restricted.
• ✔ Verify that condensate is draining properly.
• ✔ Have the system professionally inspected if comfort or performance has declined.
• ✔ If the equipment is approaching the end of its service life, compare the comfort and efficiency features available in modern through-the-wall heat pump systems.

Before assuming you need new equipment, make sure the existing system is clean, properly maintained, and operating as intended.

Sometimes the solution is a new air conditioner.

Sometimes it's simply helping the one you already have breathe properly again.

🏠 Why Proper Equipment Sizing Is Critical for Humidity Control

One of the biggest surprises for homeowners is discovering that an oversized air conditioner can actually make a room feel less comfortable, even though it may cool the space very quickly.

I hear this question all the time:

“Jake, wouldn't buying the biggest unit available cool the room faster?”

Technically, it can lower the temperature faster—but that's only part of the comfort equation.

An air conditioner doesn't just cool the air. It also removes moisture. As warm, humid indoor air passes over the cold evaporator coil, moisture condenses on the coil and is carried away through the condensate drainage system.

An oversized unit may cool the room so quickly that the thermostat reaches its set point before the system has had enough operating time to remove an appropriate amount of moisture.

• The thermostat is satisfied. The room is cool.
• But the humidity may still be relatively high.
• That's when homeowners often describe the room as “cold but sticky.”

At the other extreme, an undersized air conditioner can struggle to keep up during very hot weather. It may run for extended periods while still having difficulty reaching the desired temperature. Although longer cycles can provide more opportunity for moisture removal, an undersized system may consume more energy and experience greater operating hours and wear.

• The goal isn't to install the biggest air conditioner that will fit.
• The goal is to install the right-sized air conditioner for the space.

Proper sizing considers far more than square footage. Factors can include:

• 🧱 Insulation levels
• 📐 Ceiling height
• 🪟 Window size and orientation
• ☀️ Solar exposure
• 👨👩👧👦 Occupancy
• 🌡️ Local climate
• 💡 Internal heat sources
• 🌬️ Air leakage

Air Conditioning Contractors of America (ACCA) and other industry organizations emphasize proper load calculations and equipment selection rather than simply choosing a unit based on room size.

A properly sized system isn't necessarily the fastest system—it is the one that can balance temperature, humidity, efficiency, and operating time most effectively.

Learn more:

• 🌎 ACCA Residential Design Resources: https://www.acca.org

📊 Properly Sized vs Oversized Equipment

⚙️ Modern Controls Help Maintain Better Comfort

One of the biggest differences between older through-the-wall air conditioners and many modern heat pump systems isn't always visible from the outside.

It's the controls.