Humidifier vs Dehumidifier: Which Do You Need?

How Do I Know if I Need a Dehumidifier or Humidifier?

Humidifiers and dehumidifiers come from the word humidity. Humidity refers to the amount of water vapor in the air. While we have absolute and relative humidity, relative humidity is one commonly used.

Relative humidity is the amount of water vapor in the air expressed as a percentage of the total amount of water vapor that the air can hold at that temperature. An increase in temperature therefore translates to an increase in relative humidity and vice versa.

humidifier vs dehumidifier

Because, weather (temperature) changes throughout the year, it also means that relative humidity will also keep on changing. Sometimes there will be too much moisture in the air while sometimes the air will dry.

The ideal indoor relative humidity is between 30% and 50%. Because we don’t live in an ideal world, you will need either a humidifier or a dehumidifier to regulate the relative humidity in our homes.

So, how do you know if you need a humidifier or a dehumidifier?

Humidifiers add moisture to the air when it is too dry while dehumidifiers remove moisture from the air when it is too humid. If the relative humidity is less than 30% you need a humidifier but if it is higher than 50% you need a dehumidifier.

Relative humidity is usually low in winter so you would need a humidifier. On the other hand, summers are quite humid and you would therefore need a dehumidifier to remove some of the moisture from the air.

If your body feels sticky, there is condensation on your windows, there is mold growth in your house, your house has a musty smell, allergies are more intense, wood is rotting, wallpaper is peeling off or paint is bubbling, the relative humidity is high and you need a dehumidifier.

If you have a dry and itchy skin, itchy throat, nasal congestion, itchy throat, chapped/cracked lips, dry eyes, cracking wood/furniture and there is static electricity in your house, the relative humidity is too low and you need a humidifier.

Relative Humidity vs Weather

As I have mentioned, the decision to buy either a humidifier or dehumidifier is determined by the relative humidity levels in your house. Also, I mentioned that relative humidity is directly proportional to temperature.

What this means is that hot air has the potential to hold more moisture than cold air. That is why when you reduce the temperature of humid air, it sheds off water through a process known as condensation.

For that reason, relative humidity is usually very high in summer when temperatures are high but low in winter when temperatures are low. Seasons and temperature are however not the only factors that determine relative humidity.

Why is relative humidity in Florida way higher than in Utah, despite Utah being an arid state? To understand that, you need to ask yourself where humidity (the moisture in the air) come from.

For the relative humidity of an area to be high, the temperature needs to be high but you also need a source of water. The humidity is simply water which has evaporated from somewhere.

Although the summer temperatures in Utah are high, there is no water body to provide the air with moisture. As a result, the air there will be hot and dry (low relative humidity).

On the other hand, Florida is surrounded by the sea. Water evaporating from the sea will saturate the air, increasing the relative humidity of the area.

Relative humidity in states bordering the sea like Florida, Louisiana, Mississippi and Alaska is usually very high. For instance, the average relative humidity in Florida is 74.5% and can rise to as a high as 90% in summer.

Surprisingly, Arizona is hotter than Florida yet the average relative humidity in Arizona is 38.5%.  Other South Western states like Utah, New Mexico and Nevada are equally hot but have low relative humidity.

As you can see folks living in Florida and other humid states will need a dehumidifier in the summer to remove the excess moisture in the air. On the other hand, people living in hot and dry areas will not need a dehumidifier. A good air conditioner will do.

What happens to these 2 sets of states when winter kicks in? Remember that cold air has less potential to hold moisture than hot air.

In winter, humid states will have about 50% relative humidity which is almost perfect. In that case, the folks there will only need to run the furnace and the indoor air will be warm and comfortable. If the relative humidity rises (like in some areas in Florida), you will only need to turn on the dehumidifier.

Things will however be quite different for folks living in dry/arid areas. The air will not only be cold, but it will also be very dry.

The effects of low humidity are dry and itchy skin, dry and easily irritated eyes, cracked wood, respiratory infections, dehydration, nose bleeding, static electricity among others.

Folks living in arid areas will therefore need a humidifier especially in winter to add moisture to the air, thereby increasing the relative humidity.

Usually, the best humidity in winter is between 30% and 40%. If the relative humidity in your house is less than 30% you will need a humidifier. On the other hand, the ideal relative humidity in summer is 40-50%. If the relative humidity in your house is more than 50% you will need a dehumidifier.

Having said that, there are people who find the best indoor humidity to the most ideal at 55%. That is why some publications will list the ideal indoor humidity to be between 45% and 55%. I would however advice you to get a dehumidifier if the relative humidity is higher than 60%.

HVAC Systems vs Relative Humidity vs Humidifiers and Dehumidifiers

Your HVAC system has a direct effect on the relative humidity in the house. Let me explain how that happens.

Air conditioners are used to cool the house during the summer when the air is hot. Apart from cooling the indoor air, air conditioners also reduce the humidity of the air.

Cooling happens when warm and humid air comes into contact with the evaporator coil. The cold refrigerant inside the coil absorbs heat from the air and takes it to the condenser unit where it is released to the surrounding.

As I mentioned, when air is cooled, its potential to hold moisture drops. Therefore, when the warm indoor air is cooled, the moisture in air condenses and the condensate is drained out of the house through a drain hose.

That is how air conditioners reduce humidity. Usually, an air conditioner can remove 5 to 20 gallons of water from the air in a day.

In some areas, an air conditioner is enough to cool the air and reduce the humidity while in others you will need to run an air conditioner and a dehumidifier.

If the relative humidity in your house is still high despite having a properly sized and set air conditioner, you should invest in a dehumidifier.

If you live in a dry/arid area, you can as well opt to go with a swamp cooler also known as an evaporative cooler. Apart from cooling the air, swamp coolers also increase the indoor relative humidity.

When winter kicks in, air conditioners would have been already turned off and furnaces would be roaring. Running a furnace will lower the humidity of your indoor air since they evaporate the moisture in the air.

In some areas, you wouldn’t really mind a furnace lowering the indoor humidity but if you live in an arid area (where humidity in winter is already low) it will be a concern. In that case, you will need to buy a humidifier to inject some moisture into the air.



A humidifier is an appliance used to increase the relative humidity by adding moisture into the air. There are whole-house humidifiers for increasing humidity in the whole house and stand-alone/portable humidifiers for humidifying a single room.

So, how do you know if you need a humidifier? The following are the signs that you need a humidifier in your house:

  • Indoor relative humidity is less than 30%
  • You have dry and itchy skin
  • Your eyes are dry
  • Chapped lips
  • Respiratory infections
  • Dehydration
  • Nose bleeding
  • Nasal congestion
  • Dry and cracking wood/furniture
  • Static electricity

There are two main types of humidifiers depending on how they work. These are:

  • Cool-mist humidifiers
  • Warm-mist humidifiers

Warm-mist humidifiers use an inbuilt heating element to boil water before releasing it into the air as an invisible mist. On the other hand, cool-mist humidifiers release a mist of water at room temperature to the indoor air.

Cool-mist humidifiers are in impeller, evaporative and ultrasonic technologies. Warm-mist humidifiers are also known as steam vaporizers.

Let us now look at the different types of humidifiers in more details.

Types of Humidifiers

The following are the types of humidifiers. Please note than none is better than the other. It all depends on your budget and preference among other factors.

1. Central Humidifiers

central humidifier

As you can guess (borrowing from central ACs), central humidifiers are used to increase the humidity of the whole house. They are integrated with your HVAC system to inject moisture into the air which is then supplied throughout the house.

These are the most expensive humidifiers since they are big in size and also need to be installed by a professional HVAC technician. They are however the best choice if the air inside your whole house is dry.

2. Evaporative Humidifiers

Water (and basically all fluids) will naturally evaporate when exposed to warm and dry air. And that is exactly how evaporative humidifiers work. Actually, evaporators work very much like evaporative coolers.

They contain a wick filter, fan and a water reservoir at the bottom of the unit. The filter absorbs water from the reservoir and when the fan blows air through the moist filter, it (the air) absorbs moisture from the filter and disperses it throughout the house in form a mist.

3. Ultrasonic Humidifiers

Ultrasonic humidifiers produce mist through a diaphragm which is made to vibrate at an ultrasonic frequency. The vibrations cause water to be broken into tiny and light particles which introduces a cool mist in the room.

4. Impeller humidifiers

Impeller humidifiers use a rotating disc (at very high speed) to break down water into a cool fog which can then be released into the air. Impeller humidifiers are cheap but are not common because they are noisy and less efficient.

5. Steam Humidifiers

Steam humidifier are also known as vaporizers or warm-mist humidifiers. They use heat to increase the humidity of a room.

These units have an internal heating element and a water reservoir. They boil water until steam is formed which is then released in the indoor air.

Their operation is controlled by a humidistat which monitors the relative humidity of the indoor air. They are inexpensive but care should be taken especially if you have kids as the steam can burn the skin.

Installing a humidifier is clearly the best way to increase the humidity of a room. But how else can your increase humidity without a humidifier?

The following are the different ways of increasing humidity without a humidifier:

  • Boil water in the kitchen
  • Have bowls of water in the house
  • Shower with the bathroom door open
  • Let bathwater sit in the tub for a sometime before draining it
  • Cook on stovetop and not oven
  • Have house plants
  • Dry laundry indoors
  • Vent your dryer indoors
  • Use a spray bottle to spray water in the air
  • Place a water pot/bucket close to the furnace



A dehumidifier is an appliance used to reduce relative humidity in the air by removing some of the moisture. You can have a central/whole-house dehumidifier or a portable/stand-alone dehumidifier.

So, do you need a dehumidifier? What are the signs that you need a dehumidifier?

The following are the signs that you need a dehumidifier:

  • Relative humidity is higher than 50%
  • There is mold/mildew in the house
  • The house has a musty smell
  • Your body feels sticky and just uncomfortable
  • Allergies and asthma are worsening
  • There is rotting wood in the house
  • Condensation on windows
  • Sweating toilets
  • Blistering/bubbling paint
  • Peeling wallpaper
  • Creaky windows and doors

Types of Dehumidifiers

The following are the different types of dehumidifiers:

1. Whole-House Dehumidifiers

Whole-house dehumidifiers are also known as central dehumidifiers. They are integrated with your HVAC system and are used to reduce the relative humidity of the whole house.

As you can guess, these are the most expensive type of dehumidifiers. They are however the best option for someone who wants to regulate the humidity of every area of their home so you should have yours sized correctly.

2. Portable Dehumidifiers

As their name suggests, portable dehumidifiers can be easily moved from one room to another. Ideally, they are designed to reduce the humidity of only one room.

There are several types of portable dehumidifiers as we will see below.

3. Desiccant Dehumidifiers

Desiccant dehumidifiers reduce humidity by use of a desiccant. A desiccant is a material that attracts and holds moisture. It has a wheel (desiccant wheel) which sucks in air from the room for dehumidification.

The wheel contains silica gel (the desiccant) which absorbs moisture from the air. Most of the air that enters the unit leaves as dry air while the rest is used as reactivation air. The reactivation air is the heated to extract the moisture.

4. Thermoelectric Dehumidifiers

A thermoelectric dehumidifier uses the thermoelectric effect to convert electricity into temperature so as to effect dehumidification.

In short, warm and humid air from the room is pulled in by a fan and forced across a cool heat sink. The moisture in the air condenses and drips into a reservoir at the bottom of the unit while the less humid air is released back to the room.

5. Refrigerated Coil Dehumidifiers

Refrigerated coil dehumidifiers are also known as compressor dehumidifiers. They work pretty much like refrigerators or air conditioners.

Cold air is drawn from the room and passed through a cold coil where condensation occurs. The condensate drains into a reservoir or outside the house while the dry air is reheated and released back to the house.

As you can see, installing a dehumidifier is the best way to reduce the humidity in your house. What if you don’t have a dehumidifier?

The following are the different ways to reduce humidity in a house without a dehumidifier:

  • Use a properly sized air conditioner
  • Set AC fan to AUTO
  • Fix water leaks
  • Use vapor barriers in crawlspace
  • Close crawlspace vents
  • Dry laundry outdoors
  • Use a rock salt dehumidifier
  • Have a basket of charcoal briquettes
  • Take house plants outside.
  • Use exhaust fans
  • Take cold showers
  • Dry your rugs/carpets

Wrap Up

And basically those are the differences between humidifiers and dehumidifiers. In short, humidifiers add moisture into the air while dehumidifiers remove moisture from the air.

You will need a humidifier when relative humidity is lower than 30% and usually during the winter more so if you live in an arid area. Dehumidifiers are usually used when the relative humidity is more than 50%, usually in the summer and more so in humid areas.