Quick answer
Dehumidification is the process of removing water vapor from indoor air, usually by passing it over a cold coil so the moisture condenses and drains away.
Every central air conditioner dehumidifies as it cools. A separate dehumidifier, portable or ducted, removes moisture without needing the house to get colder.
Quick facts
The key facts about Dehumidification, with sources:
- How it works
- Air passes a coil below its dew point; water condenses and drains
- Indoor target
- Below 60% RH, ideally 30–50% 2
- Efficiency metric
- Integrated energy factor (IEF), liters per kWh 1
- ENERGY STAR savings
- Certified models use about 20% less energy 1
- Whole-home case
- Sealed homes with central air reading above 55% throughout 1
- Capacity unit
- Pints of water removed per day 1
- Refrigerant rule
- New residential dehumidifiers: 700 GWP limit from 1 Jan 2025 6
Key takeaways
- Your AC already dehumidifies; how well depends on sizing, airflow and run time 3 4.
- A dehumidifier makes sense when RH stays above 60% even with the AC working, or in a damp basement 2.
- Size portable units by how damp the space is, using ENERGY STAR's capacity table 1.
- ENERGY STAR certified dehumidifiers use about 20% less energy 1.
- Fix water sources first: leaks, grading and venting 2.
What dehumidification is
Air always holds some water vapor. When there is too much, homes feel clammy, smell musty and grow mold. Dehumidification takes that water out.
The common method is cooling. A refrigerant coil runs colder than the air's dew point. Water vapor touching the coil turns to liquid, drips into a pan, and drains away.
Your AC coil does this every time it runs. A dehumidifier does the same thing, then rewarms the dried air with the heat from its own compressor, so the room does not cool.
In HVAC terms, removing moisture is handling the "latent" load. Removing heat you can feel is the "sensible" load. A home needs both handled to be comfortable.
Moisture comes from many places. People breathe and sweat, showers and cooking release steam, and plants, aquariums and drying laundry add more.
Outdoor air leaking in carries its own moisture, which on a Gulf Coast summer day is a lot. Basements pull moisture through concrete from the soil.
A dehumidification plan starts by knowing which of these is driving your readings.
Inside a refrigerant dehumidifier
How your AC handles moisture
- The coil must get below the dew point, which takes a few minutes after start-up.
- Water must build up on the fins and drain before the cycle ends.
- Long runs remove more water. Short cycles from an oversized system remove less 3.
- Lower airflow per ton makes the coil colder and wetter. A building-science guide suggests about 400 cfm per ton in humid climates 5.
- Fan "On" between cycles can re-evaporate water from the coil back into the house.
Ways to dehumidify a home
| Method | How it works | Best for |
|---|---|---|
| Central AC | Removes moisture as it cools | Most homes in summer |
| AC with dehumidify mode | Variable-speed blower slows to wring more water | Humid climates |
| Portable dehumidifier | Plug-in unit with bucket or hose | Basements, single rooms 1 |
| Whole-home (ducted) dehumidifier | Installed unit tied to ductwork, drains to plumbing | Sealed homes reading above 55% throughout 1 |
| Ventilating dehumidifier | Brings in and dries outdoor air | Tight, humid-climate homes |
| Source control | Venting, fixing leaks, grading | Every home first 2 |
Example: how much water a dehumidifier pulls in a day
Example only. A 35-pint-per-day unit, the middle of ENERGY STAR's "very damp" range for spaces under 2,000 sq ft, running in a damp basement 1.
| Step | Math | Result |
|---|---|---|
| Rated capacity | 35 pints per day | 35 pints |
| In gallons | 35 ÷ 8 pints per gallon | About 4.4 gallons per day |
| In liters | 35 × 0.473 | About 16.6 liters per day |
| Energy at an IEF of 2.0 L/kWh (illustrative) | 16.6 ÷ 2.0 | About 8.3 kWh per day at full output |
ENERGY STAR rates dehumidifiers by integrated energy factor: liters removed per kWh, so higher is better 1.
Check the IEF on the label of the model you are considering, and use the energy savings calculator with your own electric rate.
Real removal falls as the space dries, so daily energy use is usually lower than the full-output figure.
Where you will see the term
- On dehumidifier boxes: pints per day, IEF and ENERGY STAR label 1.
- On thermostats with a "dehumidify" or "overcool" setting.
- On AC spec sheets, as sensible and latent capacity.
- In Manual J reports, as the latent load.
- In mold remediation plans.
Whole-home vs portable dehumidifiers
Whole-home
- Treats the whole house through the ducts.
- Drains to plumbing; no bucket to empty.
- Quieter in living spaces; installed out of sight.
- ENERGY STAR notes significant benefits in sealed homes with central air above 55% RH 1.
Portable
- Treats one room or area.
- Bucket needs emptying unless a hose or pump is used 1.
- Noise and heat in the room.
- Lower up-front cost and no contractor needed.
What dehumidifiers cannot fix
A dehumidifier treats the symptom. EPA's first advice is to fix the water: repair leaks, clean gutters, slope the ground away from the foundation, and vent moisture sources outdoors 2. A dehumidifier in a basement with seepage runs forever.
It also cannot fix an oversized AC on its own, though it can help. DOE's review describes a study where a small standalone dehumidifier was found to be a cost-effective way to lower indoor humidity 4. Dehumidifiers add a little heat, so in summer the AC must remove it.
Cost drivers
HyreHVAC lists no prices without enough dated quotes. For portable units, cost depends on capacity, IEF, pump or hose options and noise. For whole-home units: capacity, duct tie-in design, a dedicated drain, electrical work, controls and access.
Running cost depends on how damp the space is, how efficient the unit is, and your electric rate. ENERGY STAR certified models use about 20% less energy than conventional ones 1. See the dehumidifier installation page for what a whole-home job involves.
How to choose and set up
- Measure RH for a week with a hygrometer 2.
- Fix water sources first 2.
- Pick capacity from ENERGY STAR's damp, very damp and wet table 1.
- Choose an ENERGY STAR certified model and compare IEF 1.
- Place it away from walls if it does not discharge from the top, and keep doors and windows closed 1.
- Set the humidistat to keep RH below 60%, ideally 30–50% 2.
- For whole-home units, hire a contractor to size, duct and drain it.
Upkeep
Warning signs and when to call a pro
- RH above 60% for days with the AC running.
- The coil frosts on a portable unit in a cold basement (many have an anti-frost shutoff) 1.
- Water around a whole-home unit or its drain.
- Musty odors that persist after RH is in range: look for hidden mold or leaks.
- The AC short cycles and the house stays clammy.
Rules that apply
ENERGY STAR. The current dehumidifier specification took effect October 1, 2025. Dehumidifiers first earned the label in January 2001 1.
Refrigerants. EPA's Technology Transitions rule lists residential dehumidifiers as a subsector with a 700 GWP limit for products manufactured or imported from January 1, 2025 6. See our refrigerant transition research.
Codes. Whole-home units fall under mechanical and plumbing codes for ducts and drains. Adoption varies.
Dehumidification vs related terms
| Term | How it relates |
|---|---|
| Dehumidification | Removing moisture from air |
| Humidification | Adding moisture to air |
| Latent heat | The energy in moisture the system removes |
| Ventilation | Bringing in outdoor air, which may add or remove moisture |
Common misconceptions
- Myth A bigger AC dehumidifies better.
- Reality Oversized units run short and remove less moisture 3.
- Myth Dehumidifiers cool the room.
- Reality They warm it slightly, because the compressor's heat stays in the room.
- Myth Lower is always better.
- Reality Below 30% RH air gets uncomfortably dry; EPA's ideal is 30–50% 2.
- Myth A dehumidifier fixes a wet basement.
- Reality Fix water entry first 2.
Climate and moisture load
Humid Southeast and Gulf Coast states carry heavy moisture loads for much of the year, and many homes there benefit from a dehumidify-capable AC or a whole-home unit. Dry Southwest homes rarely need one. Basements anywhere can need a portable unit in summer.
When it matters to you
It matters when RH stays above 60%, when you see condensation or mold, or when your AC cools but the house stays sticky. Measure first, fix sources, then choose between AC settings, a portable unit and a whole-home system.
Next step: check AC sizing with the AC sizing calculator, and read about indoor air quality services.
Questions about Dehumidification
Does my air conditioner dehumidify?
Yes. As air passes the cold indoor coil, moisture condenses and drains away. How much it removes depends on run time, airflow and sizing. An oversized system that shuts off quickly removes less moisture than one that runs longer.
Do I need a whole-house dehumidifier?
ENERGY STAR says whole-home units carry significant benefits for well sealed homes with central air that see humidity above 55 percent throughout the house. If only a basement or one room is damp, a portable unit is often enough.
What size dehumidifier do I need?
Use ENERGY STAR's table. For spaces under 2,000 square feet, a slightly to moderately damp space (50 to 75 percent RH) needs about 20 to 30 pints per day, very damp needs 25 to 40, and wet needs 30 to 50. Larger spaces need more.
What should I set my dehumidifier to?
Set it to keep humidity below 60 percent, and ideally 30 to 50 percent, which is EPA's range. In basements, many people choose around 50 percent. Very low settings waste energy.
Are ENERGY STAR dehumidifiers worth it?
ENERGY STAR says certified dehumidifiers remove the same amount of moisture as similar conventional units while using about 20 percent less energy. For a unit that runs all summer, that difference adds up.
Why does my dehumidifier stop in a cold basement?
Many units have an anti-frost sensor that shuts them off when the air is too cold, because the coil can ice over. If your basement is cool, look for a model rated for lower temperatures.
Can I drain a dehumidifier into a floor drain?
Yes, if the unit has a hose fitting. ENERGY STAR notes some models let you connect a hose and run it to a floor drain, and others have a built-in pump to lift water to a sink or outdoors.
Is it better to run the AC or a dehumidifier?
In summer, a properly sized AC handles most moisture. A dehumidifier helps when the AC cools the house before it removes enough water, or in spaces the AC does not reach, like basements. The best answer depends on why humidity is high.
Does a dehumidifier help with mold?
It helps prevent mold by keeping humidity below 60 percent, which EPA advises. It does not remove mold that is already growing. EPA says to clean up mold promptly, fix the water problem, and dry wet materials within 24 to 48 hours.
Sources
- ENERGY STAR, Dehumidifiers (buying guide and capacity table), retrieved .
- U.S. EPA, A Brief Guide to Mold, Moisture and Your Home, retrieved .
- U.S. DOE Energy Saver, Central Air Conditioning (archived copy, 2025), retrieved .
- U.S. DOE Building Technologies Office, Residential HVAC Installation Practices: A Review of Research Findings (June 2018), retrieved .
- Green Building Advisor, Converting Heating and Cooling Loads to Air Flow Needs, retrieved .
- U.S. EPA, Technology Transitions HFC Restrictions by Sector, retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Capacity, IEF, the 20% figure and the spec date are from ENERGY STAR's dehumidifier page, read 10 October 2026. The worked example converts a table capacity to gallons, liters and kWh at an illustrative IEF, labelled as such; no price is computed.
Suggest a correction. We fix errors and say what changed.