What is the main difference between a humidifier and a dehumidifier?

A humidifier adds moisture to dry indoor air, while a dehumidifier removes excess moisture from damp air, so they perform opposite functions to fix opposite humidity problems.

Should I use a humidifier or a dehumidifier for a cough?

Use a humidifier for a dry cough because added moisture soothes irritated airways, but choose a dehumidifier if your cough stems from mold or mildew triggered by high indoor humidity.

Which is better for my home, a humidifier or a dehumidifier?

The better device depends on your measured indoor humidity, so use a humidifier when levels drop below 30 percent and a dehumidifier when they exceed 50 percent.

How much does it cost to run a humidifier versus a dehumidifier?

A dehumidifier costs significantly more to run because its compressor uses roughly 300 to 500 watts, whereas a typical humidifier uses only 20 to 100 watts.

Can a humidifier cause health risks if used incorrectly?

Yes, a humidifier causes health risks when overused because excessive moisture above 60 percent promotes dust mites and mold growth, so always monitor humidity levels.

Can I use a humidifier in a room that already has a dehumidifier?

No, you should not run both devices in the same room simultaneously because they directly counteract each other, wasting energy and producing no net humidity change.

What is the most common beginner mistake with a dehumidifier?

The most common beginner mistake is setting the dehumidifier too low, which over-dries the air below 30 percent and causes static shock, cracked wood, and respiratory irritation.

Is a dehumidifier just a humidifier running in reverse?

No, a dehumidifier is not a humidifier in reverse because they use different mechanisms, with dehumidifiers using refrigerant coils and humidifiers using evaporative wicks or ultrasonic vibration.

Can I switch between using a humidifier and a dehumidifier in the same season?

Yes, you can switch between them in the same season because fluctuating weather changes indoor humidity, so use a humidifier on dry days and a dehumidifier on humid days.

Which device should I use in a basement that feels damp?

Use a dehumidifier in a damp basement because basements typically trap excess moisture and stay cooler, making them prone to mold without active moisture removal.

Difference Between

Difference Between Humidifier and Dehumidifier

Written byNex Virox Team

Editorial Team

Reviewed byVarshal Nirbhavane

Senior SEO & Organic Growth Professional · 5+ years

Published: August 27, 202618 min read

Quick answer

The main difference between Humidifier and Dehumidifier is that a humidifier adds moisture to dry air, while a dehumidifier removes excess moisture from damp air. Humidifier is a device that increases indoor humidity, while Dehumidifier is a device that reduces indoor humidity.

Key takeaways

Core distinction: A humidifier adds moisture to dry air, while a dehumidifier removes excess moisture from damp air.
How each works: Humidifiers emit water vapor or steam, whereas dehumidifiers pull air over cold coils to condense water.
Seasonal fit: Use a humidifier during dry winter months, but run a dehumidifier in humid summer conditions.
Best-fit use case: Choose a humidifier for static shock or dry skin, and a dehumidifier for mold or musty smells.
Common decision mistake: Never run both simultaneously in one room, since they directly counteract each other's moisture effects.

Table of Contents18 sections

Difference Between Humidifier and Dehumidifier: Comparison Table

Aspect	Humidifier	Dehumidifier
Definition	Adds water vapor to indoor air to raise relative humidity levels.	Removes excess moisture from indoor air to lower relative humidity.
Purpose	Relieves dryness symptoms like itchy skin, static shock, and cracked lips.	Prevents mold, mildew, musty odors, and condensation on windows.
Core Mechanism	Uses ultrasonic vibration, evaporative wick, or steam to release moisture.	Uses a refrigerant coil or desiccant wheel to condense and collect water.
Target Humidity	Raises indoor humidity to the 30-50% comfort range.	Lowers indoor humidity to the 30-50% comfort range.
Ideal Season	Most useful during cold, dry winter months when heating dries air.	Most useful during hot, humid summer months or in damp basements.
Primary Output	Emits a visible or invisible mist that evaporates into room air.	Produces a bucket or drain line of collected liquid water.
Energy Source	Ultrasonic models draw around 20-30 watts; warm-mist types use more.	Compressor models typically consume 300-700 watts depending on size.
Water Source	Requires a refillable tank filled with clean tap or distilled water.	Requires an empty collection bucket or a continuous drain hose.
Water Removal Rate	Releases water into air at rates measured in gallons per day.	Extracts water rated in pints per day, commonly 20-70 pints.
Coverage Area	Small units serve one room; console models cover up to 1,000 square feet.	Portable units handle 500-4,500 square feet depending on pint capacity.
Noise Level	Ultrasonic models run nearly silent; evaporative fans produce low hum.	Compressor models emit a steady hum plus occasional compressor cycling.
Operating Temperature	Works effectively in cold winter rooms where air is naturally dry.	Compressor types lose efficiency below 65°F; desiccant types work colder.
Maintenance	Needs weekly tank cleaning to prevent mineral scale and bacteria film.	Needs filter cleaning and coil inspection every few months.
Filter Type	Evaporative wick filters capture minerals and require periodic replacement.	Air filters trap dust and must be washed or replaced regularly.
Health Benefit	Eases dry cough, congestion, and nosebleeds by moistening airways.	Reduces allergy triggers like dust mites and mold spores that thrive in dampness.
Health Risk	Overuse can breed mold and bacteria inside the tank, releasing irritants.	Over-drying can cause dry skin, irritated eyes, and respiratory discomfort.
Mold Impact	Can promote mold growth if humidity rises persistently above 60%.	Actively prevents mold by keeping surfaces and air below 50% humidity.
Static Electricity	Reduces static shocks and fabric clinging by adding moisture to air.	Can increase static electricity by making indoor air excessively dry.
Allergy Effect	May worsen dust mite allergies if humidity is pushed too high.	Helps control dust mites, which cannot survive below 50% humidity.
Energy Cost	Ultrasonic units cost only a few dollars per month to operate.	Compressor units can add noticeably to monthly electricity bills.
Purchase Price	Basic ultrasonic models start around $25-50 for small rooms.	Portable dehumidifiers typically start around $150-250.
Installation	Portable units require no installation; just fill tank and plug in.	Whole-house models need professional ductwork and drain hookup.
Portability	Small countertop and floor models are lightweight and easily moved.	Larger units have casters but remain heavy and awkward to relocate.
Climate Fit	Best for arid climates, high-altitude homes, and heated winter interiors.	Best for tropical, coastal, or rainy climates with persistent dampness.
Room Type	Commonly used in bedrooms, nurseries, and living rooms during winter.	Commonly used in basements, crawl spaces, bathrooms, and laundry rooms.
Typical User	People with dry skin, sinus issues, or homes with forced-air heating.	People with musty basements, condensation problems, or seasonal allergies.
Auto Control	Built-in humidistat turns unit off once target humidity is reached.	Built-in humidistat cycles compressor on and off to hold set level.
Water Disposal	Tank empties naturally as mist evaporates; refill frequency varies daily.	Bucket must be emptied manually or connected to a floor drain.
Key Limitation	Cannot fix structural dampness or persistent condensation problems.	Cannot add moisture to air that is already too dry.
Best-Fit Scenario	Choose when indoor humidity reads below 30% and air feels parched.	Choose when indoor humidity reads above 60% and surfaces feel clammy.

What Is Humidifier?

Humidifier is a device that adds water vapor to indoor air to raise humidity levels. It exists to relieve dryness symptoms like scratchy throats, cracked skin, static shock, and damaged wooden furniture during winter or in arid climates.

Definition of Humidifier

Humidifier is an electric or evaporative appliance that increases relative humidity in a confined space by emitting water vapor or mist. It operates through mechanisms such as ultrasonic vibration, heated steam, or fan-driven evaporation to maintain a target moisture range.

Key Characteristics of Humidifier

Characteristic	What It Means in Practice
Raises moisture	Pushes relative humidity upward, typically aiming for a 30% to 50% indoor comfort zone.
Water reservoir	Holds a tank that needs regular refilling, usually daily in dry conditions.
Mist output types	Releases either cool mist or warm steam depending on the internal heating element.
Humidistat control	Monitors current humidity and shuts off automatically once the set level is reached.
Filter requirement	Uses wicking filters or demineralization cartridges that require periodic replacement.
Energy consumption	Draws modest power, with ultrasonic models using less electricity than evaporative ones.
Noise output	Produces a gentle hum or fan sound, with ultrasonic units running nearly silent.
Coverage area	Treats a single room or small apartment, typically 200 to 500 square feet.
Maintenance burden	Needs weekly cleaning to prevent mineral scale and microbial growth inside the tank.
Health benefit	Eases dry cough, nosebleeds, and skin irritation by adding moisture to breathing air.

Common Examples of Humidifier

Levoit Classic 300S – a best-selling ultrasonic model with a 1.5-gallon tank and app-based humidity scheduling.
Vicks Warm Mist Humidifier – a steam unit that boils water and is often paired with VapoPads for congestion relief.
Honeywell HCM-350 – an evaporative wick-filter humidifier known for quiet operation and germ-free output.
Dyson AM10 – a high-end ultrasonic model that uses air multiplier technology to distribute moisture evenly.
Pure Enrichment MistAire – a compact ultrasonic unit designed for bedrooms and nursery spaces.
AprilAire 700 – a whole-house bypass humidifier mounted on a furnace duct to treat the entire home.
Carel HumiSteam – an industrial electrode steam humidifier used in commercial HVAC systems.
Philips HU4801 – an evaporative model with NanoCloud technology that releases dry, bacteria-free moisture.
Condair Mk5 – a commercial steam humidifier deployed in museums and data centers for precise climate control.
Portable travel humidifiers – small USB-powered mist units designed for hotel rooms and office desks.

Advantages and Limitations of Humidifier

Advantages	Limitations
Relieves dry skin, chapped lips, and irritated nasal passages during winter heating season.	Can breed mold and bacteria inside the tank if you skip weekly cleaning routines.
Reduces static electricity that damages electronics and causes annoying shocks on carpets.	Overuse pushes humidity above 60%, which promotes dust mite and mold growth.
Protects wooden floors, furniture, and musical instruments from cracking in dry air.	Requires constant refilling, often daily, which becomes tedious in very dry climates.
Helps you sleep better by easing snoring and throat dryness at night.	Ultrasonic models can release white mineral dust that settles on surfaces without proper filters.
Reduces transmission of airborne viruses because moist air keeps nasal mucus membranes working.	Warm mist units pose a burn risk if tipped over near children or pets.
Eases symptoms of colds and flu by keeping airways moist and comfortable.	Wick filters need replacement every one to three months, adding recurring costs.
Prevents paint, wallpaper, and plaster from drying out and cracking in heated rooms.	Does nothing to remove existing moisture problems, so it is useless in damp basements.
Operates quietly enough for nurseries and offices where background noise is unwelcome.	Requires distilled water in hard-water areas to prevent scale buildup and cloudy mist.
Helps indoor plants thrive by maintaining the humidity levels tropical species need.	Ineffective in large open-plan spaces because output cannot cover the full square footage.
Reduces dry-eye irritation and contact lens discomfort in air-conditioned rooms.	Can worsen asthma if dirty, because it disperses allergens and microorganisms into the air.

What Is Dehumidifier?

Dehumidifier is an appliance that removes excess moisture from indoor air. It pulls humid air in, cools it to condense water vapor, and releases drier air back into the room. It exists to prevent mold, mildew, musty odors, and structural damage caused by high indoor humidity.

Definition of Dehumidifier

Dehumidifier is a mechanical device that reduces and maintains the level of humidity in the air, typically by drawing air across refrigerated coils to condense water vapor into a collection tank, thereby lowering the relative humidity of an enclosed space and inhibiting microbial growth.

Key Characteristics of Dehumidifier

Characteristic	What It Means in Practice
Moisture removal	Extracts water vapor from the air and collects it in a removable bucket or drains it continuously.
Humidity control	Uses a built-in hygrometer to maintain a set relative humidity level, usually between 30% and 50%.
Air circulation	Draws room air through the unit with a fan and returns it drier, promoting even moisture distribution.
Condensation process	Cools air on refrigerant coils so water vapor turns into liquid and drips into the reservoir.
Portable design	Most units sit on casters or have handles so you can move them between damp rooms easily.
Energy consumption	Continuous compressor operation makes it one of the more power-hungry household appliances.
Noise output	Produces a steady hum from the compressor and fan, typically louder than a humidifier.
Water capacity	Collection tanks range from small 1-liter buckets to large 10-liter reservoirs depending on model size.
Continuous drainage	Offers a hose connection so water can flow directly into a floor drain instead of needing manual emptying.
Humidistat control	Automatically shuts off or cycles the compressor once the target humidity level is reached.

Common Examples of Dehumidifier

Frigidaire FFAD5033W1 – a widely sold 50-pint portable unit trusted for basements and large living spaces.
hOmeLabs 4,500 sq ft Dehumidifier – a high-capacity model popular on Amazon for whole-home moisture control.
GE APER50LZ – an Energy Star-rated 50-pint dehumidifier known for reliable performance in damp climates.
Midea 50-Pint Cube – a compact, cube-shaped unit praised for its small footprint and quiet operation.
Pro Breeze Electric Dehumidifier – a mini 250 ml unit designed for small closets, bathrooms, and RVs.
Danby 70-Pint Dehumidifier – a heavy-duty model suited for crawl spaces and unfinished basements.
Whynter ARC-110WD – a dual-hose portable unit that combines dehumidification with air conditioning.
Eva-Dry EDV-1100 – a renewable desiccant dehumidifier that uses no compressor, ideal for cold garages.
Ivation 13-Pint Dehumidifier – a compact, energy-efficient option for bedrooms, offices, and small apartments.
AprilAire E100 – a professionally installed whole-house dehumidifier that connects directly to HVAC ductwork.

Advantages and Limitations of Dehumidifier

Advantages	Limitations
Prevents mold and mildew growth by keeping relative humidity below the 60% threshold where spores thrive.	Can dry air too much if left running, causing skin irritation, static shock, and respiratory discomfort.
Reduces musty odors and improves indoor air quality in basements, bathrooms, and crawl spaces.	Requires regular emptying of the water tank, often daily in very humid conditions, unless you add a drain hose.
Protects wooden furniture, flooring, and drywall from warping, cracking, and rot caused by excess moisture.	Consumes significant electricity, which can noticeably raise monthly utility bills during continuous operation.
Helps alleviate allergy and asthma symptoms by reducing dust mites, which cannot survive below 50% humidity.	Generates noticeable noise from the compressor and fan, which can be disruptive in bedrooms or quiet spaces.
Prevents condensation on windows, walls, and pipes, reducing water damage and peeling paint.	Loses efficiency in cold rooms below 65°F because coils can frost over, reducing moisture extraction.
Deters pests like silverfish, cockroaches, and termites that require damp environments to survive.	Requires regular filter and coil cleaning to maintain performance; neglect leads to reduced airflow and efficiency.
Speeds up drying of damp laundry and prevents musty smells in closets and wardrobes.	Adds heat to the room as a byproduct of the condensation process, making warm spaces feel warmer.
Protects electronics, books, documents, and musical instruments from humidity-related damage.	Can be heavy and bulky, making it difficult to move between floors or rooms without planning.
Reduces the need for chemical mold treatments by addressing the root cause of dampness.	Initial purchase cost is higher than a humidifier, with quality portable units ranging from $150 to $300.
Maintains a consistent, comfortable indoor environment during humid summer months.	Does not filter out airborne pollutants or allergens; it only removes moisture, not dust or pollen.

Similarities Between Humidifier and Dehumidifier

Shared Aspect	How Humidifier and Dehumidifier Are Alike
Air treatment goal	Both a humidifier and a dehumidifier actively modify indoor air to reach a more comfortable moisture level.
Device category	A humidifier and a dehumidifier are both classified as household appliance units designed for environmental control.
Primary input	Both the humidifier and the dehumidifier require electrical power and surrounding room air to operate.
Water handling	Both a humidifier and a dehumidifier manage water, either by adding moisture or collecting it.
Target users	Homeowners, allergy sufferers and parents commonly use both a humidifier and a dehumidifier indoors.
Room placement	A humidifier and a dehumidifier both operate best when placed on a flat floor surface away from walls.
Health motivation	Both the humidifier and the dehumidifier are frequently purchased to relieve respiratory symptoms or allergies.
Seasonal use	Both a humidifier and a dehumidifier see heaviest usage during specific seasons when indoor humidity shifts.
Humidity measurement	Both a humidifier and a dehumidifier rely on relative humidity readings to gauge current room conditions.
Hygrometer integration	Many models of both the humidifier and the dehumidifier include a built-in hygrometer for monitoring.
Auto shutoff	Both a humidifier and a dehumidifier commonly feature automatic shutoff when water levels reach limits.
Adjustable settings	A humidifier and a dehumidifier both offer variable speed or output controls for user preference.
Target humidity range	Both the humidifier and the dehumidifier aim to keep indoor relative humidity near the 30-50% comfort zone.
Energy consumption	Both a humidifier and a dehumidifier draw continuous electricity and contribute to monthly energy bills.
Filter requirement	Both the humidifier and the dehumidifier often use filters that need periodic cleaning or replacement.
Water source	Both a humidifier and a dehumidifier work with tap water, though distilled water is often recommended.
Cleaning need	A humidifier and a dehumidifier both require regular cleaning to prevent mold and bacteria buildup.
Noise output	Both the humidifier and the dehumidifier generate audible operational noise during normal running cycles.
Portable design	Both a humidifier and a dehumidifier come in portable sizes that users can move between rooms.
Capacity rating	Both the humidifier and the dehumidifier are rated by how much water they process per day.
Coverage area	Both a humidifier and a dehumidifier are sized according to the square footage they can effectively serve.
Safety certification	Both the humidifier and the dehumidifier carry electrical safety certifications for household use.
Operational cost	Both a humidifier and a dehumidifier incur ongoing costs for electricity, filters and maintenance supplies.
Mold risk	Both a humidifier and a dehumidifier can develop mold growth if their water tanks are neglected.
Maintenance routine	Both the humidifier and the dehumidifier need periodic draining, wiping and descaling of internal parts.
Thermostat pairing	Both a humidifier and a dehumidifier can work alongside a smart thermostat for automated humidity control.
Smart controls	Both the humidifier and the dehumidifier offer app or voice control in newer connected models.
Long-term outcome	Both a humidifier and a dehumidifier aim to protect furniture, wood and health by stabilizing humidity.
Purchase channels	Both a humidifier and a dehumidifier are sold through the same big-box retailers and online marketplaces.
Warranty coverage	Both the humidifier and the dehumidifier typically include a one-year manufacturer warranty on parts.

Humidifier or Dehumidifier: Which Should You Choose?

The single variable that decides it for most people is your indoor relative humidity level. Measure it with a hygrometer. If your home reads below 30-40%, choose Humidifier. If it reads above 50-60%, choose Dehumidifier. Your comfort goal is simply to stay inside that healthy 30-50% range.

When to Use Humidifier

Choose Humidifier when your air is dry, typically under 30% relative humidity. You will notice static shocks, cracked wooden furniture, or persistent dry skin and bloody noses. Use one during winter months when heating systems strip moisture, or if you live in a desert climate. It is also the right tool for relieving congestion from colds or allergies.

When to Use Dehumidifier

Choose Dehumidifier when your air feels damp or muggy, typically above 50-60% relative humidity. You will see condensation on windows, musty odors, or visible mold and mildew growth. Use one in basements, bathrooms, or crawl spaces, and during hot, humid summer months. It is also essential for protecting stored belongings from moisture damage or preventing dust mite populations.

Common Misconceptions About Humidifier and Dehumidifier

Common Myth	The Reality
A humidifier and a dehumidifier do the exact same job.	A humidifier adds moisture to dry air, while a dehumidifier removes moisture from damp air.
You only need a humidifier in winter.	A humidifier helps year-round in dry climates, air-conditioned rooms, and high-altitude homes.
You only need a dehumidifier in summer.	A dehumidifier works in any season when indoor humidity stays above 60 percent.
Running a humidifier will make your room warmer.	A humidifier adds moisture, not heat; it does not raise air temperature.
Running a dehumidifier will make your room colder.	A dehumidifier removes moisture and may release slight heat, so it rarely cools a room.
Humidifiers and dehumidifiers can be used at the same time.	Running both at once wastes energy because the humidifier adds moisture the dehumidifier removes.
You can use a humidifier to fix mold on walls.	A humidifier adds moisture that feeds mold; a dehumidifier reduces mold growth.
You can use a dehumidifier to fix dry skin.	A dehumidifier dries air further; a humidifier relieves dry skin and itchy eyes.
A humidifier cleans the air in your room.	A humidifier adds water vapor; it does not filter dust, pollen, or pollutants.
A dehumidifier purifies the air you breathe.	A dehumidifier removes moisture, not airborne particles; it is not an air purifier.
You should fill a humidifier with hot tap water.	Hot water can release minerals and bacteria; use distilled or cool water in a humidifier.
Bigger is always better for a dehumidifier.	An oversized dehumidifier short-cycles and leaves humidity high; match capacity to room size.
A humidifier will cure your asthma completely.	A humidifier eases dry-air symptoms but cannot cure asthma; excess moisture can trigger it.
A dehumidifier will cure allergies completely.	A dehumidifier reduces dust mites and mold but cannot remove pollen or pet dander.
You never need to clean a humidifier.	Uncleaned humidifiers grow mold and bacteria that get sprayed into your air.
You never need to clean a dehumidifier.	Dirty dehumidifier coils and buckets breed mold and reduce moisture removal efficiency.
A humidifier works fine with the windows wide open.	Open windows let moisture escape outdoors, so the humidifier cannot raise indoor humidity.
A dehumidifier works fine with the windows wide open.	Open windows let humid outdoor air in, so the dehumidifier works harder and less effectively.
You can place a humidifier right next to your bed.	Placing a humidifier close to bedding can wet fabrics and promote mold growth.
You can place a dehumidifier right next to a wall.	A dehumidifier needs airflow on all sides; wall placement blocks intake and reduces performance.
A humidifier will fix a musty smell in your basement.	Musty smells come from dampness; a humidifier worsens it, while a dehumidifier helps.
A dehumidifier will fix a dry cough in winter.	A dehumidifier dries air further; a humidifier adds moisture that soothes a dry cough.
You can leave a humidifier running with an empty tank.	Running a humidifier dry can damage the unit and create a fire or burn hazard.
You can leave a dehumidifier running with a full bucket.	A full bucket triggers auto-shutoff; ignoring it stops dehumidification until emptied.
Humidifiers only help people, not houseplants.	Humidifiers benefit tropical houseplants that need 50 percent or higher humidity.
Dehumidifiers only help basements, not bedrooms.	Bedrooms above 60 percent humidity benefit from a dehumidifier to reduce dust mites.
You should run a humidifier at 100 percent power always.	Humidity above 60 percent encourages mold; aim for 30 to 50 percent with a humidifier.
You should run a dehumidifier at 100 percent power always.	Over-drying below 30 percent causes static, dry skin, and cracked wood; use a hygrometer.
Humidifiers and dehumidifiers use the same amount of electricity.	Dehumidifiers typically draw more power than humidifiers, especially in warm rooms.
You can judge humidity by how your skin feels.	Skin feel is unreliable; use a hygrometer to decide between a humidifier and a dehumidifier.

Conclusion

Difference Between Humidifier and Dehumidifier comes down to moisture direction: one adds water vapor to dry air, the other removes excess moisture. Choose a humidifier when your air feels dry and static shocks occur. Choose a dehumidifier when you face musty smells, mold, or sticky humidity.

FAQs on Difference Between Humidifier and Dehumidifier

What is the main difference between a humidifier and a dehumidifier?: A humidifier adds moisture to dry indoor air, while a dehumidifier removes excess moisture from damp air, so they perform opposite functions to fix opposite humidity problems.
Should I use a humidifier or a dehumidifier for a cough?: Use a humidifier for a dry cough because added moisture soothes irritated airways, but choose a dehumidifier if your cough stems from mold or mildew triggered by high indoor humidity.
Which is better for my home, a humidifier or a dehumidifier?: The better device depends on your measured indoor humidity, so use a humidifier when levels drop below 30 percent and a dehumidifier when they exceed 50 percent.
How much does it cost to run a humidifier versus a dehumidifier?: A dehumidifier costs significantly more to run because its compressor uses roughly 300 to 500 watts, whereas a typical humidifier uses only 20 to 100 watts.
Can a humidifier cause health risks if used incorrectly?: Yes, a humidifier causes health risks when overused because excessive moisture above 60 percent promotes dust mites and mold growth, so always monitor humidity levels.
Can I use a humidifier in a room that already has a dehumidifier?: No, you should not run both devices in the same room simultaneously because they directly counteract each other, wasting energy and producing no net humidity change.
What is the most common beginner mistake with a dehumidifier?: The most common beginner mistake is setting the dehumidifier too low, which over-dries the air below 30 percent and causes static shock, cracked wood, and respiratory irritation.
Is a dehumidifier just a humidifier running in reverse?: No, a dehumidifier is not a humidifier in reverse because they use different mechanisms, with dehumidifiers using refrigerant coils and humidifiers using evaporative wicks or ultrasonic vibration.
Can I switch between using a humidifier and a dehumidifier in the same season?: Yes, you can switch between them in the same season because fluctuating weather changes indoor humidity, so use a humidifier on dry days and a dehumidifier on humid days.
Which device should I use in a basement that feels damp?: Use a dehumidifier in a damp basement because basements typically trap excess moisture and stay cooler, making them prone to mold without active moisture removal.