If Your AC Isn’t Doing Enough, Get a Dehumidifier

If your room feels muggy and damp even though the temperature is where you want it to be, “this means that your [air conditioner’s] indoor coil isn’t getting cold enough,” explained Brice Allen Bowley, senior director of engineering at GE Appliances. “It needs to drop below the dew point before it really starts removing moisture.”

This problem is particularly common with oversize air conditioners. But even if your AC is sized just right for your space, it might still struggle to dehumidify the room at the same rate that it cools the air down. To get the coils cold enough to dehumidify, your air conditioner might try to overcool the room.

This is not only uncomfortable but is also a waste of energy. “The core problem here is that the sensible and latent load are coupled,” Bonner explained, “and we’ve only got one tool to handle both of those unique problems.”

Most window air conditioners, for example, have a sensible heat ratio of 0.7, which means they put 70% of their energy toward sensible cooling, reserving the other 30% for dehumidification. Variable-speed inverter ACs like the models we recommend are much more energy-efficient, but they also tend to put an even larger portion of that energy toward cooling — sometimes up to 90%, depending on how fast the compressor is running.

Those ratios might work for people who live in dry or even moderate climates. But I live in New England, just a few miles away from the Atlantic Ocean. As I write this, it’s 81 degrees Fahrenheit outside with a relative humidity level of 79%. My Frigidaire FFAD2234W1 dehumidifier has a hose that drains directly into the sump pump, and on days like this, conditions are so humid that I still have to manually empty the water tank.

Still, I’d rather lug that bucket to the sink a few times a year than deal with the moist, musty chill of an air conditioner that can’t keep up with the latent load.

A dehumidifier helps a lot in the shoulder seasons, aka that “second summer” that often hits in the fall, as well as the transition time (in Boston, at least) from April to May. You know, that time of year when it’s not too hot, not too cold, and all you need is a light jacket.

But on those temperate days, the heightened humidity can quickly reach a point where it’s not so pleasant anymore. “It’s something you almost don’t notice,” said Bonner. “You’re sticky and sweaty, but you’re not really hot. You feel it on the fabrics instead.”

Once you start to sweat, you might be tempted to run the air conditioner. But you would end up wasting a ton of energy, because your AC would need to overcool the room to really dehumidify it. An example from testing: To cool my home from 70 to 65 degrees Fahrenheit on a muggy April day, my heat pump typically uses around 800 watts per hour. If I run the dehumidifier instead, it uses about a quarter of the energy and ultimately leaves my home feeling much more comfortable.

A dehumidifier can certainly complement your AC, but it’s hardly a substitute. In fact, there are times when it might actually work against your air conditioner.

For one thing, a dehumidifier has to pump the exhaust heat out into the room, which could increase the air temperature over time. The idea of warming a space in order to cool it more comfortably may seem slightly contradictory. But if you come home to a hot, muggy house after a summer day out, it might be your only option.

To get around that problem, Bonner suggests using the machines at different times of day: running your dehumidifier in the morning, for example, before turning the air conditioner on in the afternoon. “That way, you can sort of ‘pre-dehumidify’ the air,” he explained. “You knock out all the moisture and get the room to a comfortable level before you start to cool it.”

If you’re already considering buying a new air conditioner, some new machines have their own built-in features to help you better balance your latent and sensible loads. A lot of the more recent models we’ve tested and recommended are better than their predecessors at dehumidifying, specifically.

Window units like the Midea U or U Plus and the Frigidaire Gallery GHWW085TE1 come with dedicated dehumidification settings, as do all of our portable AC picks (including our new upgrade pick, the Frigidaire Gallery GHPH142AA1) and almost every heat pump. Some of these models also have auto settings that allow the AC to seamlessly switch between cooling and moisture-removal modes depending on the conditions in your home. (This can help to mitigate your mold concerns, too.) You can even use the built-in smart-home scheduling tools on these systems to automate your daily pre-dehumidification ritual.

In spite of those new built-in features, our testing has shown that the most effective option — as in, the fastest results, plus the ability to dial in the exact temperature and humidity you want — is ideally to have one tool to handle your sensible load and another, separate device to deal with the latent load.

But as long as you’re paying attention to the humidity level in your home, it will ultimately make your air conditioning, and your life, much more comfortable.

This article was edited by Harry Sawyers and Megan Beauchamp.