Dehumidifiers vs Air Conditioners
Short answer
Dehumidifier vs air conditioner: the A/C removes heat and some moisture, a dehumidifier removes only moisture, and in humid heat you often need the second to hold indoor humidity in EPA's 30% to 50% range.
Swelter Almanac, checked against the sources · updated
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Points on this page
The forecast in brief
- EPA says to use air conditioners and/or dehumidifiers as needed to keep indoor humidity under 60%, ideally 30% to 50% (EPA).
- ENERGY STAR sizes portable units by dampness: 20 to 30 pints a day for a slightly damp small or medium room, 50-plus for a wet large one (ENERGY STAR).
- Since DOE's 2019 test change, units are rated at 65°F instead of 80°F, so an old 50-pint model is about a 30-pint model today (ENERGY STAR).
- ENERGY STAR-certified dehumidifiers remove the same moisture as similar conventional units while using 20% less energy.
- A whole-home unit suits well-sealed homes with central air that read above 55% humidity consistently (ENERGY STAR).
- Never run drain water near electrical circuits, and plug the unit into a properly grounded outlet (ENERGY STAR).
Dehumidifier vs air conditioner: what does each do?
An air conditioner lowers temperature and pulls moisture out as water condenses on its cold coil, while a dehumidifier removes moisture and gives back a little heat. ENERGY STAR notes that a dehumidifier slightly warms the air around it, so it never replaces the A/C in summer. EPA's mold guide simply says to use one, the other or both as needed.
The catch with A/C alone is timing. ENERGY STAR's room air conditioner page warns that an oversized unit "will cool the room before it has a chance to remove the humidity," and recommends a low fan speed on humid days because slower air removes more moisture (ENERGY STAR). When the A/C cannot keep up with moisture, a dehumidifier fills the gap.
What humidity should a dehumidifier or air conditioner hold?
Hold indoor relative humidity between 30% and 50%, and never let it sit above 60%, per EPA. ENERGY STAR adds that anything above 50% may promote mold growth. DOE Building America's sizing guidance uses 75°F and 50% humidity as the indoor design condition for Manual J load calculations.
Every ENERGY STAR dehumidifier has a built-in humidistat: set it near 45% to 50% and the unit cycles itself. If yours lacks a readout, ENERGY STAR suggests hanging a separate hygrometer nearby so you can see when to run it. If the whole house runs high, the humid heat overview covers where else the moisture may come from.
What size dehumidifier do you need?
Size a portable dehumidifier by how damp the space is and how big it is, in pints of water removed per day. ENERGY STAR's chart, below, runs from 20 to 30 pints for a slightly damp small or medium room to 50-plus for a wet large space, and the agency says it is better to oversize than undersize. If you are replacing a unit, it suggests judging by how much water you empty each day.
Watch the label year. DOE's 2019 test procedure moved testing from 80°F to 65°F to reflect basement conditions, so pint ratings dropped: an old 50-pint unit is about 30 pints now, and an old 70-pint unit is about 40 to 45. The new metric, integrated energy factor, also counts power used while the unit is cycled off. ENERGY STAR's version 6.0 portable criteria, effective October 1, 2025, require at least 1.70, 2.01 or 3.30 liters per kWh depending on capacity (criteria).
Portable or whole-house dehumidifier?
Choose a portable unit for one damp room and a whole-house unit when the entire house stays humid despite working central air. ENERGY STAR describes whole-home dehumidifiers as ducted, usually permanent systems that suit humid climates and relatively well-sealed homes with central air reading above 55% consistently. They cost more, and ENERGY STAR advises hiring a contractor to size and install one.
Before buying either, check the A/C. A system that is oversized or runs its fan on ON can leave a house damp that a properly set system would dry; see why the A/C leaves the house clammy. ENERGY STAR also notes that sealing the house and its ducts improves a whole-home unit's performance and cuts its energy use.
How do you drain a dehumidifier?
Drain a dehumidifier by emptying its bucket, running a hose by gravity to a floor drain or sump, or sending the water to a condensate pump when no drain sits lower than the unit. ENERGY STAR says most portables have a full-bucket light and automatic shutoff, and some accept a hose so you never empty the bucket. Whole-home units usually have only a drain connection, which an HVAC professional routes to a floor drain or condensate pump during installation.
A condensate pump collects water in a small reservoir and pushes it up and out to a drain, which helps in basements and closets with no floor drain. Supply-house condensate pump listings (PlumbingSupplyAndMore, owned by the people who run Swelter Almanac) show what these small pumps look like. Follow the pump maker's instructions for the outlet and any overflow safety switch, and never defeat that switch.
Electrical safety comes first. ENERGY STAR says never to set up drainage near electrical circuits or devices, to use a properly grounded outlet, to keep hoses away from cords and to place the unit close enough to the drain that the hose does not become a tripping hazard. If you're unsure, call a licensed technician.
When does a dehumidifier beat a bigger air conditioner?
For moisture alone, a dehumidifier usually makes more sense than a bigger A/C, because extra cooling capacity makes moisture control worse, not better. ENERGY STAR says an oversized room unit wastes energy and does not cool better, and DOE Building America ties short-cycling in humid climates to poor humidity control (Building America). For room units, the room A/C sizing chart keeps you from overbuying.
Get the most from the dehumidifier you have. ENERGY STAR advises closing doors and windows to the room while it runs, keeping it away from dust that clogs coils, and leaving space around units without top discharge. Below 65°F, frost can form on the coils; switch the unit off to defrost or choose a model rated for lower temperatures. Cut moisture at the source too: vent the dryer outdoors, run bath and kitchen fans, clear gutters and fix dripping outdoor faucets. If water has already soaked something, EPA says dry it within 24 to 48 hours.
Ceiling fans make damp air feel better without drying it; see ceiling fan direction for the summer setting. And in dry desert heat, the problem flips: there, adding moisture is how swamp coolers cool.
| Condition without dehumidification | Small to medium room (under 2,000 sq ft) | Large room (over 2,000 sq ft) |
|---|---|---|
| Slightly to moderately damp, 50–75% RH | 20–30 | 30+ |
| Very damp, 75–90% RH | 25–40 | 40+ |
| Wet, 90–100% RH | 30–50 | 50+ |
Dehumidifier numbers
- 20%less energy for the same moisture removal, ENERGY STAR modelsENERGY STAR
- 65°Ftest temperature since DOE's 2019 procedure, down from 80°FENERGY STAR
- 30 pintstoday's approximate rating for an old 50-pint unitENERGY STAR
- 55%sustained reading that makes a whole-home unit worth a lookENERGY STAR
How this page was put together
Sources are ENERGY STAR's dehumidifier, testing-and-capacity, key-criteria and room air conditioner pages, EPA's mold guide and DOE Building America's equipment-sizing document, read in October 2026. No brand comparisons, prices or lab tests are included; sizing follows ENERGY STAR's chart as published.
More questions
Can a dehumidifier cool a room?
No. ENERGY STAR notes a dehumidifier slightly warms the air around it, though drier air can feel more comfortable at the same temperature.
Why is my new 35-pint dehumidifier labeled smaller than my old 50-pint one?
DOE's 2019 test moved from 80°F to 65°F, so ratings dropped. ENERGY STAR estimates an old 50-pint unit is about 30 pints under the new test.
Where should a portable dehumidifier go?
In the dampest room, with doors and windows closed, away from dust, and with space around it unless it blows out the top. Keep the drain hose clear of cords and outlets.
Does a dehumidifier need a condensate pump?
Only if you want continuous drainage and no drain sits below the unit. Otherwise empty the bucket or run a short hose to a floor drain or sump.
What humidity setting should I choose?
Pick a point in EPA's 30% to 50% range. Start near the top of it in summer, then lower the setting if rooms still smell musty.
Will a whole-house dehumidifier work without central air?
ENERGY STAR describes whole-home units as using the home's ducts, and recommends them for homes with central air. Without ducts, portables in the problem rooms are the usual answer.
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