Too much moisture in a home shows up in familiar ways: a musty basement, condensation on windows, sticky air in summer, peeling paint or mold spots in closets and corners. A dehumidifier fixes the problem by pulling water out of the air, but the right type depends on how big the problem is and where it is. This guide explains how to tell whether you need a dehumidifier, how portable and whole-house units differ, how capacity ratings work, and what to plan for when you install one.
Do you need a dehumidifier?
The EPA recommends keeping indoor relative humidity (RH) below 60%, and ideally between 30% and 50%, to discourage mold, dust mites and moisture damage. An inexpensive hygrometer will tell you where you stand. Common signs you need dehumidification:
- Humidity readings consistently above 55–60%
- Musty or earthy smells, especially in basements and crawl spaces
- Condensation on windows, cold water pipes or ducts
- Mold or mildew on walls, ceilings, closets or stored items
- Warped wood floors, sticking doors or peeling paint
- Rooms that feel clammy even when the air conditioner is running
Fix the source first. A dehumidifier treats the air, not the cause. Check gutters and downspouts, grading around the foundation, dryer and bath fan venting, plumbing leaks and crawl space vapor barriers. Fixing these can shrink the dehumidifier you need, or remove the need entirely.
Portable vs whole-house: the main differences
| Portable dehumidifier | Whole-house dehumidifier | |
|---|---|---|
| Coverage | One room or one open area | Whole home or large zone (basement, crawl space, entire floor) |
| Installation | Plug in; no installation | Ducted into the HVAC system or a dedicated duct system; usually professional install |
| Drainage | Bucket, or hose to a floor drain; some have a built-in pump | Permanent condensate drain or condensate pump |
| Noise | In the room with you | Usually in a mechanical room, basement or crawl space |
| Control | Built-in humidistat on the unit | Wall or system control; often integrates with the thermostat |
| Maintenance | Empty bucket, clean filter | Replace filter, check drain, periodic coil inspection |
| Best for | Renters, single damp rooms, seasonal use | Humid climates, whole-home problems, finished basements, encapsulated crawl spaces |
When a portable dehumidifier makes sense
Portable dehumidifiers are the simplest option. Choose one if:
- The problem is limited to one room, such as a basement, laundry room or bedroom.
- You rent, or can't modify the HVAC system.
- You only need dehumidification part of the year.
Things to look for:
- Continuous drain option: A hose connection to a floor drain saves emptying the bucket. If the drain is higher than the unit, look for a model with a built-in pump or add a condensate pump.
- Low-temperature operation: Basements are often cool. Some units handle cool temperatures better and include auto-defrost to keep the coil from icing.
- ENERGY STAR certification: Certified models remove more water per kilowatt-hour, which matters for a unit that may run for months.
- Auto-restart: Resumes operation after a power outage.
When a whole-house dehumidifier makes sense
A whole-house (whole-home) dehumidifier is a larger, permanently installed unit. It typically sits in a basement, attic, crawl space or mechanical room and connects to ductwork. Consider one if:
- You live in a humid climate and the whole house feels damp, not just one room.
- Your air conditioner cools the house but doesn't remove enough moisture. This is common with oversized AC systems and in tight, energy-efficient homes during mild, humid weather.
- You have a finished basement or an encapsulated crawl space that needs year-round humidity control.
- You're tired of emptying buckets and moving portable units from room to room.
Whole-house units can run independently of heating and cooling, so they dry the air even when the thermostat isn't calling for cooling. Honeywell Home's DR90A3000 90-pint whole-home dehumidification system is one example of a ducted unit designed for this kind of installation.
Understanding capacity: pints per day
Dehumidifier capacity is rated in pints of water removed per day. There's one important catch: in 2019, the U.S. Department of Energy changed the test conditions for portable dehumidifiers from 80°F and 60% RH to 65°F and 60% RH. Cooler air holds less moisture, so the same machine now gets a lower rating. Roughly:
- An older "70-pint" unit is about a "50-pint" unit under the current test.
- An older "50-pint" unit is about a "35-pint" unit.
- An older "30-pint" unit is about a "22-pint" unit.
When you compare models or read older sizing charts, check which test standard the rating uses. Whole-house units are rated under their own test conditions, so read the manufacturer's spec sheet for the coverage area and conditions behind each number.
How to size a dehumidifier
Size depends on the space and how damp it is. As a rough guide for portable units (current DOE ratings):
- Small to medium room, moderately damp (musty smell, high readings in humid weather): about 20–35 pints per day.
- Large room or basement, very damp (condensation, damp spots on walls or floor): about 35–50 pints per day.
- Wet basement (seepage, standing water after rain): fix the water entry first, then consider a large portable unit or a whole-house unit.
For whole-house units, sizing depends on the conditioned square footage, how airtight the house is, local climate and moisture sources. Manufacturers publish coverage guidelines for each model, and an HVAC contractor can size the unit based on your home's actual latent (moisture) load. When you're between sizes, the larger unit runs less often, but don't oversize to the point of wasted cost and space.
Installation and drainage
Portable
- Place the unit with clearance around the air intake and outlet, and keep doors and windows closed while it runs.
- Run the drain hose to a floor drain or sump with a continuous downward slope, or use a condensate pump to lift water to a sink or drain.
Whole-house
- Ducting: Common setups pull air from the return side and supply dried air back into the supply duct, or run as a standalone system with its own ducts. Follow the manufacturer's installation diagrams.
- Drain: Plan a permanent condensate drain to a floor drain, sump or condensate pump. Many local codes regulate where condensate can discharge.
- Power and controls: Typically requires a dedicated outlet or circuit, plus a dehumidistat or compatible thermostat control. Electrical work must follow local code.
- Service access: Leave room to change the filter and service the unit.
A licensed HVAC contractor is usually the best choice for whole-house installation, because the unit ties into ductwork, controls and sometimes the air handler.
Maintenance tips
- Clean or replace the filter on the schedule in the owner's manual. A clogged filter cuts airflow and capacity.
- Keep drain lines and pump reservoirs clean to avoid clogs and overflow.
- Check the humidistat setting each season. Around 45–50% RH is a common target in summer.
- Inspect the coil for dust buildup or icing.
What about humidifiers?
In cold climates, the opposite problem often shows up in winter: dry air, static shocks and dry skin. Whole-house humidifiers (bypass, fan-powered and steam types) add moisture through the HVAC system. Some homes need a dehumidifier in summer and a humidifier in winter, with both controlled to keep RH in a comfortable range.
Quick decision checklist
- Measure humidity with a hygrometer for a week or two.
- Fix moisture sources (drainage, leaks, venting) first.
- One damp room or a rental: a portable unit with a continuous drain.
- Whole home, finished basement or encapsulated crawl space: a whole-house unit, professionally sized and installed.
- Plan drainage and power before you buy.
Compare options in our whole-house dehumidifiers collection, browse all dehumidifiers and humidifiers, and add a condensate pump if your drain is above the unit. Not sure which model fits your home? Contact our team with your square footage and the area you want to dry.