Humidity Control

Humidity control keeps indoor moisture within a useful range. In humid weather, that may mean removing water from the air with a whole-home dehumidifier. During a dry winter, it may mean adding moisture with a whole-home humidifier.

The EPA generally recommends indoor relative humidity between 30 and 50 percent. That’s a good starting range, but it isn’t one perfect setpoint for every home, climate, or season.

Relative humidity changes with temperature. The same amount of moisture can produce a different relative humidity reading when the temperature changes. That’s why we may also look at dew point and outdoor conditions when evaluating a home.

During cold weather, a home with older windows or weak insulation may need a lower humidity setting to prevent condensation. If water forms on windows, walls, or attic surfaces, the indoor humidity may be too high for the building envelope.

The number on the thermostat isn’t the only thing that matters. We also look at where the moisture goes.

Signs Of High Indoor Humidity

High humidity can make a home feel warmer, sticky, or heavy even when the thermostat shows a normal temperature.

You may also notice:

• Musty odors
• Condensation on windows or ducts
• Mold or mildew around vents and closets
• Damp basement or crawlspace odors
• Wood floors that cup or swell
• Paint that peels or bubbles
• Bedding that feels damp
• Rust on metal surfaces
• An air conditioner that cools but doesn’t remove enough moisture

High humidity can support mold growth, dust mites, and other biological contaminants. Keeping indoor humidity below 60 percent, and ideally near 30 to 50 percent when practical, is part of the EPA’s moisture-control guidance.

A dehumidifier can help control moisture in the air, but it can’t repair a roof leak, foundation problem, plumbing leak, or wet crawlspace.

Fix the water first.

Signs Of Low Indoor Humidity

Low humidity is most common during winter. Cold outdoor air holds little moisture. Once that air enters the home and is heated, its relative humidity can become very low.

Signs may include:

• Static shocks
• Dry skin, eyes, nose, or throat
• Gaps appearing in wood floors
• Shrinking or cracking woodwork
• Musical instruments going out of adjustment
• A home that feels colder than the thermostat setting

Adding moisture may improve comfort and help protect certain wood materials. However, too much humidification can cause condensation inside walls, attics, windows, or ductwork.

More isn’t better.

How We Determine What You Need

A single humidity reading doesn’t tell the whole story. Humidity changes through the day and may vary between the basement, main floor, bedrooms, and attic.

Our evaluation may include:

• Measuring temperature and humidity in several areas
• Reviewing readings over multiple days
• Looking at indoor dew point
• Checking for window condensation
• Inspecting for water leaks or standing water
• Evaluating basement and crawlspace conditions
• Checking bathroom and kitchen exhaust
• Confirming the dryer vents outdoors
• Inspecting the air conditioner and evaporator coil
• Measuring HVAC airflow and static pressure
• Reviewing equipment size and run time
• Looking for duct leakage
• Checking fresh-air ventilation
• Reviewing thermostat and fan settings

An oversized air conditioner may cool the home quickly and shut off before it removes enough moisture. Incorrect airflow can also affect dehumidification. ASHRAE notes that excessive cooling airflow can reduce moisture removal, while airflow that is too low can freeze the coil.

Sometimes humidity improves after correcting airflow, refrigerant charge, controls, duct leakage, or equipment operation. A separate dehumidifier may not be needed.

In other homes, especially during mild but damp weather, the air conditioner may not run long enough to control humidity. That’s where a dedicated whole-home dehumidifier can help.

Installing A Whole-Home Dehumidifier

A whole-home dehumidifier pulls moist air across a cold coil. Water condenses and drains away. The unit then sends warmer, drier air back into the home or HVAC system.

The equipment must be sized for the home’s moisture load, not just square footage. Climate, basement conditions, ventilation, air leakage, number of occupants, and the building envelope all affect that load.

Installation may include:

• A dedicated return-air grille
• A connection to the HVAC return or supply
• Properly sized and sealed ductwork
• A trapped condensate drain
• A condensate pump when gravity drainage isn’t available
• An overflow switch or water safety
• A replaceable filter
• A whole-home humidity controller
• Integration with fresh-air ventilation
• Enough access for service

The discharge air from a dehumidifier is warmer because the unit removes moisture and rejects heat back into the air. That’s normal. The installation needs to place that air where it won’t overheat a small room or create comfort problems.

The condensate line should be pitched, trapped, secured, and tested. A dehumidifier that removes water from the air and then leaks it onto the floor has missed the assignment.

After installation, we verify airflow, drainage, controls, and humidity response.

Installing A Whole-Home Humidifier

Whole-home humidifiers may use bypass, fan-powered, or steam technology.

Bypass and fan-powered models move air across a wet pad. Steam systems boil water and inject controlled steam into the air. Steam can provide more capacity and work under a wider range of operating conditions, but it usually requires more electrical power and maintenance.

A correct installation considers:

• The home’s size and air leakage
• Available duct space
• Water quality
• Water-supply connections
• Drain requirements
• Electrical capacity
• Airflow direction
• Steam absorption distance
• Blower operation
• Outdoor temperature
• Condensation risk
• Access for pad or canister replacement

The control should prevent the humidifier from operating when conditions aren’t right. In colder climates, an outdoor-temperature sensor or automatic reset control can lower the humidity setting as outdoor temperatures fall.

Steam distribution tubes need proper placement and drainage. Water shouldn’t collect in the duct. Pads, water panels, canisters, valves, and drains also require inspection and replacement.

Maintenance And Seasonal Adjustments

Humidity equipment deals with water, which means maintenance isn’t optional.

Dehumidifier filters need cleaning or replacement. Drain lines and traps should be inspected. Coils may need cleaning, and water safety switches should be tested.

Humidifiers can collect mineral scale. Pads or steam canisters need replacement based on water quality and use. Valves, drains, and distribution tubes should be checked for leaks or blockage.

Humidity settings may also need seasonal adjustment. A setting that works in October may cause window condensation during a January cold snap.

Is Humidity Control Right For Your Home?

Humidity control can improve comfort and help reduce moisture conditions that support biological growth. It can also help protect wood floors, furniture, finishes, and parts of the HVAC system.

It isn’t a cure for mold, allergies, asthma, or building leaks. If mold or water damage is already present, the source needs to be corrected and the affected material may need professional remediation.

American Air Purification can help determine whether your problem comes from the HVAC system, the building, outdoor air, an active moisture source, or a mix of several issues. We’ll connect you with a qualified local Installation Partner who can size, install, test, and maintain the right equipment.

Humidity is a whole-home problem. It deserves a whole-home evaluation.